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Fog chemistry in the Texas–Louisiana Gulf Coast corridor
Abstract
Fog samples were collected in two population centers of the US Gulf Coast (Houston, Texas and Baton Rouge, Louisiana) using Caltech active strand cloud collectors. A total of 32 fogwater samples were collected in Baton Rouge (November 2004–February 2005) and Houston (February 2006). These samples were analyzed for pH, total and dissolved organic carbon, major inorganic ions, and a variety of organic compounds including organic acids, aromatics, carbonyls, and linear alkanes. Fogs in both environments were of moderate density, with typical fog liquid water contents <100 mg m−3. Fog samples collected in Houston reflect a clear influence of marine and anthropogenic inputs, while Baton Rouge samples also reflect agricultural inputs. The volume-weighted mean fog pH was somewhat more acidic (∼4.3) in Houston than in Baton Rouge (∼5.0). A wide pH range was observed in fog at both locations. Houston fog had higher concentrations of Cl−, NO3−, Na+, Mg2+, and Ca2+. Sulfate to nitrate ratios were high in fogs at both locations, typical of many clouds in the eastern US. Total organic carbon concentrations were much higher in Houston fogs than in Baton Rouge fogs. Efforts to speciate dissolved organic carbon (DOC) reveal large contributions from organic acids and carbonyls, with smaller contributions from other organic compound families including aromatics, alkanes, amides, and alcohols. Approximately 40% of the fog DOC was unspeciated in samples from both study locations.
... Fog is a form of cloud touching the earth's surface, causing a reduction in visibility to less than 1000 m (Klemm et al. 2012;Mu and Zhang 2014). Fog droplets interact with both particles (inorganic and organic) and soluble gases and eventually help in the removal of pollutants and nutrients from the atmosphere by drop deposition onto the ground (Collett et al. 2008;Li et al. 2011). In India, thick fog engulfs the entire region of north India in December and January during the winter season. ...
... Fog water was collected using Caltech Active Strand Cloudwater Collector (CASCC2; Collett et al. 2008) installed at a height of nearly 15 m from the ground at the rooftop of SES in JNU, New Delhi and the rooftop of a residential building in DCRUST, Murthal, Sonipat ( Fig. 1) to avoid interference from the deposition of ambient particles through resuspension or other local disturbances. Sampling was done during the winter seasons for 2 years, 2015-16 and 2016-17. ...
... Also soil and plants emit acetate ), which may be another source. Formate and acetate are emitted from local sources as there is little evidence of their long-range transport (Raja et al. 2008). Organic acids in fog samples of New Delhi were higher than in Sonipat samples. ...
In this study, fog water samples collected from New Delhi and its satellite township Sonipat for 2 years 2015–16 and 2016–17 are characterized by soluble ions and internal buffering capacity. The pH of fog water is close to 5.6 due to the limited contributions of Ca2+ and Mg2+ ions by virtue of low wind speed during winters. NH4+ and Ca2+ were dominant cations in fog at both sites during both sampling years. NH4+ and Ca2+ contributions were similar in New Delhi during 2015–16, but Ca2+ increased during 2016–17 on account of construction activities. Emissions from agriculture fields through fertilizer applications and animal breeding lead to an increase of NH4+ compared to Ca2+ at Sonipat. SO42− was comparable with Cl−, followed by NO3− ions. Plastic burning in this region during wintertime was a possible source of Cl− ions. Acid neutralization decreases as NH4+ > Ca2+ and Mg2+ for all samples in Sonipat and as Ca2+ > NH4+ and Mg2+ in New Delhi. Higher NO3− in New Delhi was due to vehicular emissions. Vehicular emissions in New Delhi and agriculture fields in Sonipat were dominant sources of organic acids. Observed internal buffering capacity was different than theoretical values over a pH range from 4 to 7 in New Delhi, whereas both buffering capacities were close to each other in Sonipat samples. Lead in fog water at both sites was higher than prescribed safe limits for drinking water. Pollution sources were responsible for higher concentrations of metals, organic acids, and soluble ions in fog in New Delhi compared to that in Sonipat.
... Until now, our knowledge on the physics of fog remains limited, including the numerous physical processes influencing fog formation, development, and decay. Although the physical processes of fog, such as droplet microphysics [10][11][12][13][14][15][16], aerosol physics and chemistry [17][18][19][20][21], radiation [22,23], turbulence [24][25][26][27], large/small-scale dynamics [28][29][30][31], and surface conditions [32][33][34][35][36] have been widely investigated, the uncertainty of typical numerical forecast models estimating VIS is higher than 50% [37][38][39]. As to VIS estimation methods in meteorological operations, some forecasting methods provide pure mathematical statistical fitting without the explicit consideration of physical processes [40], such as climatological statistical methods [41], the rule-based statistical method [42,43], numerical model ensemble [39,44,45] and machine learning methods [43,46]. ...
... VIS-LWC scheme verified and the local fitting formula and the VIS less than 1 km (a) and the wide-range VIS data (b) (VIS_obs, VIS_K84, VIS_Gultepe, fitting curve of VIS represent the observed VIS, simulated VIS with Equation(19), Equation(20) and the local fitting, respectively).Most of the visibility values simulated by the visibility parameterization schemes are ...
... VIS-LWC scheme verified and the local fitting formula and the VIS less than 1 km (a) and the wide-range VIS data (b) (VIS_obs, VIS_K84, VIS_Gultepe, fitting curve of VIS represent the observed VIS, simulated VIS with Equation(19), Equation(20) and the local fitting, respectively). ...
Low visibility, associated with fog, severely affects land, marine, and air transportation. Visibility is an important indicator to identify different intensities of fog; therefore, improving the ability to forecast visibility in fog is an urgent need for social and economic development. Establishing a proper visibility parameterization scheme is crucial to improving the accuracy of fog forecast operation. Considering various visibility impact factors, including RH, Nd, D, LWC, the parameterization formula of visibility in fog, as well as their performance in meteorology operation, are reviewed. Moreover, the estimated ability of the visibility parameterization formulas combined with the numerical model is briefly described, and their advantages and shortcomings are pointed out.
... Other than inorganic soluble ions, formate and acetate ions have also been reported in atmospheric condensate, rainfall or other form of precipitation like fog and dew (Willey and Wilson, 1993;Khwaja, 1995;Khare et al., 2000;Herckes et al., 2013). Formate concentrations are found to be more than acetate in dew water due to more solubility of formate at lower pH in comparison to acetate (Khare et al., 2000;Raja et al., 2008). However, there is a lack of information about tartrate and citrate ions in fog and dew, which could be linked to their limited concentration (in ng m -3 ) in atmospheric aerosols (Rohrl and Lammel, 2002;Tsai et al., 2013) or otherwise not attempted. ...
... The dew samples had lower concentration when compared to fog in absolute terms as (Tsai et al., 2013) or it may be emitted from vegetation and soil as reported by Wang et al. (2007). Formic and acetic acids are of local origin since there is lack of long range transport of acetic acid and formic acid (Raja et al., 2008). The formate and acetate ratio in all the studied fog and dew samples were less than 1 indicating that vehicular emissions being dominant source. ...
... Vehicles emits more of acetic acid compared to formic acid (Avery et al., 2001;Raja et al., 2008 and references therein). The high pH of samples further helped dissolution of more acetate than formate which could be possibly as formic acid (pKa = 3.75) dissolves more when pH is low (Khare et al., 2000;Raja et al., 2008). ...
Fog and dew, formed via different formation mechanisms, are suitable to study the liquid-gas-solid phase chemical interactions in the ambient atmosphere. A total of 24 fog and 19 dew samples were collected using Caltech Active Strand Cloud water Collector 2 and dew condensers, respectively, over New Delhi during winter months of 2014–15 and were characterised for pH and soluble inorganic ion using ion chromatograph. Dew samples were alkaline (pH = 6.26 ± 0.37) in comparison to natural rainwater pH of 5.6 and fog collected at rooftop (pH = 5.38 ± 1.3) and at ground level (pH = 5.96 ± 0.3). The volume weighted mean equivalents of cations followed the order NH4⁺ > Ca²⁺ > Mg²⁺~K⁺ > Na⁺ and of anions as SO4²⁻ > NO3–~Cl– > HCO3– > F– > NO2– in fog whereas the order for dew was Ca²⁺ > NH4⁺ > Na⁺ > K⁺ > Mg²⁺ and SO4²⁻~HCO3– > Cl– > NO2– > NO3– > F–. The Ca²⁺ ions were higher than NH4⁺ in dew while NH4⁺ was higher than Ca²⁺ in fog. Nitrite was higher in comparison to nitrate in dew while this was reverse in fog. Alkaline pH of dew samples might have played a role in the gas phase transfer and the base catalyzed transformation of NOx to HONO and subsequent dissolution of HONO in dew in comparison to fog. Acidity was caused more by sulphate ions (SO42–/NO3– ratio was 2.2 and 4.18 for fog and dew, respectively) but was effectively neutralised. Neutralisation factors were different in fog (NH4⁺ > Ca²⁺ > Mg²⁺) and dew (Ca²⁺ > NH4⁺ > Mg²⁺). The differences in the fog and dew composition are primarily linked to their formation processes.The agricultural fields and fossil fuel combustion were sources for ammonium, sulphates, nitrate and nitrite whereas locally resuspended crustal materials added calcium and magnesium carbonates. Vehicular and plant emissions, biomass burning and the oxidation of volatile organic compounds seems to be responsible for higher organic acids in dew and fog.
... After weighing for 10 volume determination, the samples were pooled, aliquots for different chemical analyses were taken and aliquots as well as leftover samples were stored at −20 • C until analysis. For size-resolved droplet sampling a 3-stage collector (Raja et al., 2008) with nominal D 50 of 22, 16, and 4 µm for stages 1, 2, and 3, respectively, was used. This collector is basically a size-fractionating version of the CASCC, using Teflon strands/banks 15 with different diameters and different spacing in the 3 stages. ...
... Literature data from 3-stage cloud 20 water collectors is very sparse. Raja et al. (2008) report decreasing concentrations of main ions with increasing drop size for fog samples in the US Gulf coast region, obtained with the same collector as in the present study. Collett et al. (1995) observed U-type profiles in cloud samples obtained with a different 3-stage collector (different nominal cut-offs) from two sites in North Carolina and California, USA. ...
... 1for the main cloud events. DOC was converted to DOM (dissolved organic matter) using a conversion factor of 1.8 as in previous studies(Giulianelli et al., 2014;Benedict et al., 2012;Straub et al., 2012;Collett et al., 2008). Solute concentrations are always dominated by the main ions sulfate, nitrate, and ammonium, explaining approx. ...
Cloud water samples were taken in September/October 2010 at Mt. Schmücke in a rural, forested area in Germany during the Lagrange-type Hill Cap Cloud Thuringia 2010 (HCCT-2010) cloud experiment. Besides bulk collectors, a 3-stage and a 5-stage collector were applied and samples were analysed for inorganic ions (SO42−, NO3−, NH4+, Cl−, Na+, Mg2+, Ca2+, K+), H2O2 (aq), S(IV), and dissolved organic carbon (DOC). Campaign volume-weighted mean concentrations were 191, 142, and 39 μmol L−1 for ammonium, nitrate, and sulfate, respectively, between 4 and 27 μmol L−1 for minor ions, 5.4 μmol L−1 for H2O2 (aq), 1.9 μmol L−1 for S(IV), and 3.9 mgC L−1 for DOC. The concentrations compare well to more recent European cloud water data from similar sites. On a mass basis, organic material (as DOC · 1.8) contributed 20–40 % (event means) to total solute concentrations and was found to have non-negligible impact on cloud water acidity. Relative standard deviations of major ions were 60–66 % for solute concentrations and 52–80 % for cloud water loadings (CWLs). Contrary to some earlier suggestions, the similar variability of solute concentrations and CWLs together with the results of back trajectory analysis and principal component analysis, suggests that concentrations in incoming air masses (i.e. air mass history), rather than cloud liquid water content (LWC) was the main factor controlling bulk solute concentrations at Mt. Schmücke. Droplet effective radius was found to be a somewhat better predictor for cloud water total ionic content (TIC) than LWC, even though no single explanatory variable can fully describe TIC (or solute concentration) variations in a simple functional relation due to the complex processes involved. Bulk concentrations typically agreed within a factor of 2 with co-located measurements of residual particle concentrations sampled by a counterflow virtual impactor (CV) and analysed by an aerosol mass spectrometer (AMS), with the deviations being mainly caused by systematic differences and limitations of the approaches (such as outgassing of dissolved gases during residual particle sampling). Scavenging efficiencies (SEs) of aerosol constituents were 0.56–0.94, 0.79–0.99, 0.71–98, and 0.67–0.92 for SO42−, NO3−, NH4+, and DOC, respectively, when calculated as event means with in-cloud data only. SEs estimated using data from an upwind site were substantially different in many cases, revealing the impact of gas-phase uptake (for volatile constituents) and mass losses across Mt. Schmücke likely due to physical processes such as droplet scavenging by trees and/or entrainment. Drop size-resolved cloud water concentrations of major ions SO42−, NO3−, and NH4+ revealed two main profiles: decreasing concentrations with increasing droplet size and "U"-shapes. In contrast, profiles of typical coarse particle mode minor ions were often increasing with increasing drop size, highlighting the importance of a species' particle concentration size distribution for the development of size-resolved solute concentration patterns. Concentration differences between droplet size classes were typically < 2 for major ions from the 3-stage collector and somewhat more pronounced from the 5-stage collector, while they were much larger for minor ions. Due to a better separation of droplet populations, the 5-stage collector was capable of resolving some features of solute size dependencies not seen in the 3-stage data, especially sharp concentration increases (up to a factor of 5–10) in the smallest droplets for many solutes.
... Among the most common methods of characterizing the organic fraction of cloud water samples is total organic carbon (TOC) analysis. Irrespective of whether studies have been focused on cloud water or fog water, most work has shown the following: (i) TOC is enhanced in air masses with higher anthropogenic influence (Collett et al., 1998;Deguillaume et al., 2014;Herckes et al., 2013;Raja et al., 2009); (ii) ∼ 40 %-85 % of TOC is attributed to unidentified species (Benedict et al., 2012;Boris et al., 2016Boris et al., , 2018Herckes et al., 2002;Raja et al., 2008); (iii) organic acids usually account for 15 % of TOC (Deguillaume et al., 2014;Gioda et al., 2011;Straub et al., 2007); (iv) monocarboxylic acids are more abundant than dicarboxylic acids (Löflund et al., 2002); and (v) acetic and formic acids are the most dominant organic acids contributing to TOC Gioda et al., 2011). Most of the aforementioned studies focused on fog, motivating a closer look at cloud water, as solute concentrations depend on the type of aqueous medium (Fig. 1). ...
... In terms of the chemical profile of the speciated organics, the order in decreasing contribution of C mass relative to TOC was as follows (±1 standard deviation): acetate (14.7 ± 20.5 %), formate (5.4 ±,9.3 %), oxalate (2.8 ± 4.3 %), DMA (1.7 ± 6.3 %), succinate (1.6 ± 2.4 %), pyruvate (1.3 ± 4.5 %), glycolate (1.3 ± 3.7 %), adipate (1.0 ± 3.6 %), MSA (0.1 ± 0.1 %), glutarate (0.1 ± 0.2 %), and maleate (< 0.1 ± 0.1 %). Approximately 70.0 % of TOC went unaccounted for, highlighting the complexity and difficulty of organic speciation in the study region, with this value being fairly similar to other regions (Benedict et al., 2012;Boris et al., 2016Boris et al., , 2018Herckes et al., 2002;Raja et al., 2008). Monocarboxylic acids dominated the speciated organic mass (∼ 75 %) and were about 4 times more abundant than dicarboxylic acids, which is suggestive of a higher abundance of gaseous species and precursors. ...
This work focuses on total organic carbon (TOC) and contributing species in cloud water over Southeast Asia using a rare airborne dataset collected during NASA's Cloud, Aerosol and Monsoon Processes Philippines Experiment (CAMP2Ex), in which a wide variety of maritime clouds were studied, including cumulus congestus, altocumulus, altostratus, and cumulus. Knowledge of TOC masses and their contributing species is needed for improved modeling of cloud processing of organics and to understand how aerosols and gases impact and are impacted by clouds. This work relies on 159 samples collected with an axial cyclone cloud-water collector at altitudes of 0.2–6.8 km that had sufficient volume for both TOC and speciated organic composition analysis. Species included monocarboxylic acids (glycolate, acetate, formate, and pyruvate), dicarboxylic acids (glutarate, adipate, succinate, maleate, and oxalate), methanesulfonic acid (MSA), and dimethylamine (DMA). TOC values range between 0.018 and 13.66 ppm C with a mean of 0.902 ppm C. The highest TOC values are observed below 2 km with a general reduction aloft. An exception is samples impacted by biomass burning for which TOC remains enhanced at altitudes as high as 6.5 km (7.048 ppm C). Estimated total organic matter derived from TOC contributes a mean of 30.7 % to total measured mass (inorganics + organics). Speciated organics contribute (on a carbon mass basis) an average of 30.0 % to TOC in the study region and account for an average of 10.3 % to total measured mass. The order of the average contribution of species to TOC, in decreasing contribution of carbon mass, is as follows (±1 standard deviation): acetate (14.7 ± 20.5 %), formate (5.4 ± 9.3 %), oxalate (2.8 ± 4.3 %), DMA (1.7 ± 6.3 %), succinate (1.6 ± 2.4 %), pyruvate (1.3 ± 4.5 %), glycolate (1.3 ± 3.7 %), adipate (1.0 ± 3.6 %), MSA (0.1 ± 0.1 %), glutarate (0.1 ± 0.2 %), and maleate (
... Size-resolved cloud water samples were collected using a three-stage Caltech Active Strand Cloud water Collector (CASCC) (Demoz et al., 1996), with 50% collection efficiency cut-off diameters (D 50 ) of 22, 16, and 4 µm for stage 1, stage 2 and stage 3 respectively (Raja et al., 2008;Spiegel et al., 2012). Cloud droplets entering the collector were separated to different size fractions and captured by the given impaction obstacles. ...
... Schmucke (Van Pinxteren et al., 2016). Raja and co-workers (Raja et al., 2008) found that major ions were concentrated in small droplets. The tendencies of Ca 2+ and Mg 2+ may explained by their source, soil dust. ...
Greenhouse Gas (GHG) emissions decoupling from economic growth are imperative goals for sustainable development. This study combines decoupling index and Log Mean Divisia Index (LMDI) to study which major transformation is required in the way energy is produced, delivered and consumed in order to achieve decoupling in Taiwan. The results indicate that a high-energy price can improve the energy structure by inciting energy efficiency use and result in decoupling CO2 emissions from economic growth. Targeting CO2 emissions through early action is the best approach to acquire decoupling. An annual energy intensity decrease of 2.4% is key for Taiwan to achieve absolute decoupling by 2020. The study suggests that the Taiwan government should focus on energy efficiency through investing in clean energy innovation at an early phase. Taiwan should consider national policies that are sensitive to effective economic strategies that enhance research and development and also invest in promoting energy efficiency in the economy-wide.
... Glycolic acid (GA) is the smallest α-hydroxyacid and is highly water-soluble. Ambient hydroxyl monocarboxylic acids including LA and GA have been identified in precipitation (Kieber et al., 2002), fog/cloud water (Raja et al., 2008;Sorooshian et al., 2013), and snow pack samples (Kawamura et al., 2012). Fisseha et al. (2004) identified LA in the gas and aerosol phases from photooxidation of 1,3,5-trimethylbenzene in smog chamber experiments. ...
... Production of LA and GA in aerosol water associated with microbial activity is very likely because some microorganisms produce LA and GA (Kataoka et al., 2001;Raja et al., 2008). Cabredo et al. (2009) reported that LA bacteria (lactobacillus), which produce LA as the major metabolic end product of carbohydrate fermentation, accounted for ∼ 21 % of total airborne bacteria. ...
Lactic acid (LA) and glycolic acid (GA), which are low-molecular-weight
hydroxyacids, were identified in the particle and gas phases within the
marine atmospheric boundary layer over the western subarctic North Pacific.
A major portion of LA (81%) and GA (57%) was present in the particulate
phase, which is consistent with the presence of a hydroxyl group in these
molecules leading to the low volatility of the compounds. The average
concentration (±SD) of LA in more biologically influenced marine
aerosols (33 ± 58 ng m−3) was substantially higher than that in
less biologically influenced aerosols (11 ± 12 ng m−3). Over the
oceanic region of phytoplankton blooms, the concentration of aerosol LA was
comparable to that of oxalic acid, which was the most abundant diacid during
the study period. A positive correlation was found between the LA
concentrations in more biologically influenced aerosols and chlorophyll a in
seawater (r2 = 0.56), suggesting an important production of aerosol
LA possibly associated with microbial (e.g., lactobacillus) activity in
seawater and/or aerosols. Our finding provides a new insight into the poorly
quantified microbial sources of marine organic aerosols (OAs) because such
low-molecular-weight hydroxyacids are key intermediates for OA formation.
... After weighing for volume determination, the samples were pooled, aliquots for different chemical analyses were taken and aliquots as well as leftover samples were stored at −20 • C until analysis. For size-resolved droplet sampling a three-stage collector (Raja et al., 2008) with nominal D 50 of 22, 16, and 4 µm for stages 1, 2, and 3 respectively was used. This collector is basically a size-fractionating version of the CASCC, using Teflon strands/banks with different diameters and different spacing in the three stages. ...
... Literature data from three-stage cloud water collectors is very sparse. Raja et al. (2008) report decreasing concentrations of main ions with increasing drop size for fog samples in the US Gulf Coast region, obtained with the same collector as in the present study. Collett et al. (1995) observed U-type, profiles in cloud samples obtained with a different three-stage collector (different nominal cut-offs) from two sites in North Carolina and California, USA. ...
Cloud water samples were taken in September/October 2010 at Mt. Schmücke
in a rural, forested area in Germany during the Lagrange-type Hill Cap Cloud
Thuringia 2010 (HCCT-2010) cloud experiment. Besides bulk collectors, a
three-stage and a five-stage collector were applied and samples were analysed for
inorganic ions (SO42−,NO3−, NH4+, Cl−,
Na+, Mg2+, Ca2+, K+), H2O2 (aq), S(IV), and
dissolved organic carbon (DOC). Campaign volume-weighted mean concentrations
were 191, 142, and 39 µmol L−1 for ammonium, nitrate, and
sulfate respectively, between 4 and 27 µmol L−1 for minor ions,
5.4 µmol L−1 for H2O2 (aq), 1.9 µmol L−1
for S(IV), and 3.9 mgC L−1 for DOC. The concentrations compare well to
more recent European cloud water data from similar sites. On a mass basis,
organic material (as DOC × 1.8)
contributed 20–40 % (event means) to total
solute concentrations and was found to have non-negligible impact on cloud
water acidity. Relative standard deviations of major ions were 60–66 % for
solute concentrations and 52–80 % for cloud water loadings (CWLs). The
similar variability of solute concentrations and CWLs together with the
results of back-trajectory analysis and principal component analysis,
suggests that concentrations in incoming air masses (i.e. air mass history),
rather than cloud liquid water content (LWC), were the main factor controlling
bulk solute concentrations for the cloud studied. Droplet effective radius
was found to be a somewhat better predictor for cloud water total ionic
content (TIC) than LWC, even though no single explanatory variable can fully
describe TIC (or solute concentration) variations in a simple functional
relation due to the complex processes involved. Bulk concentrations
typically agreed within a factor of 2 with co-located measurements of
residual particle concentrations sampled by a counterflow virtual impactor
(CVI) and analysed by an aerosol mass spectrometer (AMS), with the deviations
being mainly caused by systematic differences and limitations of the
approaches (such as outgassing of dissolved gases during residual particle
sampling). Scavenging efficiencies (SEs) of aerosol constituents were
0.56–0.94, 0.79–0.99, 0.71–98, and 0.67–0.92 for SO42−,
NO3−, NH4+, and DOC respectively when calculated as
event means with in-cloud data only. SEs estimated using data from an upwind
site were substantially different in many cases, revealing the impact of
gas-phase uptake (for volatile constituents) and mass losses across Mt.
Schmücke likely due to physical processes such as droplet scavenging by
trees and/or entrainment. Drop size-resolved cloud water concentrations of
major ions SO42−, NO3−, and NH4+ revealed two
main profiles: decreasing concentrations with increasing droplet size and
“U” shapes. In contrast, profiles of typical coarse particle mode minor
ions were often increasing with increasing drop size, highlighting the
importance of a species' particle concentration size distribution for the
development of size-resolved solute concentration patterns. Concentration
differences between droplet size classes were typically < 2 for
major ions from the three-stage collector and somewhat more pronounced from the
five-stage collector, while they were much larger for minor ions. Due to a
better separation of droplet populations, the five-stage collector was capable
of resolving some features of solute size dependencies not seen in the
three-stage data, especially sharp concentration increases (up to a factor of
5–10) in the smallest droplets for many solutes.
... This value is intermediate between values measured in fog and cloud samples from Southeast Asia (Mount Tai: pH 3.68, Wang et al., 2011; Jeju Island, Korea: pH 5.2, Kim et al., 2006; Daekwanreung, Korea: pH 4.7, Kim et al., 2006; and Shanghai, China: pH 5.97, Li et al., 2011a). Major inorganic species contributing to the measured acidity of the fog water at BYI (Table 1; Fig. 3) were NH + 4 (mean concentration of 2220 µM), followed by NO − 3 (1260 µM) and SO −2 4 (730 µM); these concentrations were elevated compared to fog and cloud samples collected globally (e.g., Collett et al., 2002; Raja et al., 2008; Wang et al., 2011). Sea salt was also an abundant constituent of the fog water (mean concentrations of 551 µM Na + and 253 µM Cl − ), as was organic matter (mean 276 µM, estimated using a molecular mass of 100 g mol −1 and OM/OC=1.8 ...
... Zhang et al., 2005). The mean NH + 4 concentration measured at BYI was within the upper range of measured NH + 4 in fog and cloud samples (similar to, for example, the Po Valley, Italy (Fuzzi et al., 1992) and Baton Rouge, Louisiana; Raja et al., 2008). Although agriculture was a main land use on BYI, no correlation between wind direction and fog NH + 4 concentrations was observed (Fig. SI-1 in the Supplement), suggesting long-range transport of fine particle NH + 4 as an important source. ...
Samples of fog water were collected at Baengnyeong Island (BYI) in the Yellow Sea during the summer of 2014. The most abundant chemical species in the fog water were NH4+ (mean of 2220μM), NO3- (1260 μM), SO4-2 (730 μM), and Na+ (551 μM), with substantial contributions from other species consistent with marine and biomass burning influence on some dates. The pH of the samples ranged between 3.48 and 5.00, with a mean of 3.94, intermediate within pH values of fog/cloud water reported previously in Southeast Asia. Back trajectories (72 h) showed that high relative humidity (> 80%) was encountered upwind of the sampling site by all but one of the sampled air masses, and that the fog composition at BYI can be impacted by several different source regions, including the Sea of Japan, southeastern China, northeastern China, and the East China Sea. Sulfur in the collected fog was highly oxidized: low S(IV) concentrations were measured (mean of 2.36 μM) in contrast to SO4-2 and in contrast to fog/cloud S(IV) concentrations from pollutant source regions; organosulfate species were also observed and were most likely formed through aging of mainly biogenic volatile organic compounds. Low-molecular-mass organic acids were major contributors to total organic carbon (TOC; 36-69%), comprising a fraction of TOC at the upper end of that seen in fogs and clouds in other polluted environments. Large contributions were observed from not only acetic and formic acids but also oxalic, succinic, maleic, and other organic acids that can be produced in aqueous atmospheric organic processing (AAOP) reactions. These samples of East Asian fog water containing highly oxidized components represent fog downwind of pollutant sources and can provide new insight into the fate of regional emissions. In particular, these samples demonstrate the result of extensive photochemical aging during multiday transport, including oxidation within wet aerosols and fogs.
... Although fog can act as an effective and natural cleansing agent for air pollutants, several studies around the world have reported a link between air pollution and fog formation [Kokkola et al., 2003;Tiwari et al., 2011;Syed et al., 2012]. Field studies at various locations on both bulk and size-resolved chemical composition of fog water have been conducted Raja et al., 2008;Ehrenhauser et al., 2012;Herckes et al., 2014] along with studies on its effects on physicochemical aerosol properties, such as size distribution, chemical composition, and elemental ratios [Das et al., 2008;Ge et al., 2012]. The majority of the earlier studies focused on inorganics present inside fog water [Munger et al., 1983;Pandis et al., 1990;Forkel et al., 1995;Hoag et al., 1999]. ...
... IIT Kanpur is located 8 km from the city center but within the boundary of the city. A three-stage Caltech Active Strand Cloud Collector (CASCC) [Raja et al., 2008;Kaul et al., 2011] with 50% cutoff diameters of 22 μm, 16 μm, and 4 μm [Kaul et al., 2011] from the first to third stages, respectively, was used to collect droplet size-resolved fog water samples. In this study stage cutoff diameters are taken as diameters for coarse (C), medium (M), and fine (F) droplets. ...
Size-resolved fog water samples were collected in two consecutive winters at Kanpur, a heavily polluted urban area of India. Samples were analyzed by an aerosol mass spectrometer after drying and directly in other instruments. Residues of fine fog droplets (diameter: 4–16 μm) are found to be more enriched with oxidized (oxygen to carbon ratio, O/C = 0.88) and low volatility organics than residues of coarse (diameter > 22 μm) and medium size (diameter: 16–22 μm) droplets with O/C of 0.68 and 0.74, respectively. These O/C ratios are much higher than those observed for background ambient organic aerosols, indicating efficient oxidation in fog water. Accompanying box model simulations reveal that longer residence times, together with high aqueous OH concentrations in fine droplets, can explain these trends. High aqueous OH concentrations in smaller droplets are caused by their highest surface-volume ratio and high Fe and Cu concentrations, allowing more uptake of gas phase OH and enhanced Fenton reaction rates, respectively. Although some volatile organic species may have escaped during droplet evaporation, these findings indicate that aqueous processing of dissolved organics varies with droplet size. Therefore, large (regional, global)-scale models need to consider the variable reaction rates, together with metal-catalyzed radical formation throughout droplet populations for accurately predicting aqueous secondary organic aerosol formation.
... During a rain event, rainwater sample was collected after 30 min À1 h interval depending upon the rain intensity, and a minimum of 50 ml rainwater was collected per rain event to make sure that various kinds of analysis can be performed on these samples. Fog water samples were also collected via Caltech 3 stage fog water collector for 2012e2015 winter (Decem-bereFebruary) period in 3 size fractions; coarse, medium and fine with 50% size cutoffs at 22, 16, 4 mm, respectively (Kaul et al., 2011;Raja et al., 2008). Immediately after collection, fog, and rainwater samples were filtered through 0.22 mm Whatman Nylon membrane filters to remove suspended insoluble particles. ...
... During rain events, AA (ANR ¼ 0.87) are found to be slightly more acidic than dry periods (ANR ¼ 1.04), mostly because of increased contribution from sulfate. Cloud processing is an important source of atmospheric sulfate (Moore et al., 2004;Raja et al., 2008), so it's possible that additional sulfate was produced inside the cloud and then came down with the precipitation, thus increasing its net concentration. No/little change in AA composition during rain events indicates that rain can equally efficiently remove all aerosols species. ...
... The water-soluble ion and WSOC concentrations in this study are comparable to those at other mountain sites in southern China (Sun et al., 2010(Sun et al., , 2015. The tracer for in-cloud aqueous-phase reactions, oxalate, had average concentrations of 0.28 mg L 1 in Cloud 2018 and 0.73 mg L 1 in Cloud 2020, accounting for 1.2% and 2.3%, respectively, of the WSOC (calculated by the mass of carbon in oxalate) and are consistent with previous studies (∼1-3%) Raja et al., 2008;Stahl et al., 2021). Similar to cloud water, aerosols were also dominated by SNA and WSOM, which represented more than 80% of the mass concentration of all detected species. ...
The formation process of in‐cloud aqueous‐phase secondary organic matter (aqSOM) and its characteristics are unclear. Herein, water‐soluble inorganic ions, oxalate, and water‐soluble organic carbon (WSOC) were determined in cloud water and aerosol (PM2.5) samples simultaneously collected at a remote mountain site in southern China during spring 2018 and winter 2020. The molecular compositions of water‐soluble organic matter (WSOM) in cloud water and aerosols were analyzed by a Fourier transform ion cyclotron resonance mass spectrometer in negative electrospray ionization (ESI‐) mode. The results showed that the mean concentration of WSOC was 6.27–8.54 mg C L⁻¹ in cloud water and 0.60–1.37 μg C m⁻³ in aerosols. The strong correlation observed between WSOM and aqueous secondary matter (e.g., NO3⁻ and oxalate), the positive matrix factorization results, and the elevated WSOM/K⁺ ratios observed in cloud water suggested enhanced aqSOM formation in cloud water. According to random forest analysis, the factors related to in‐cloud WSOM variation mainly included secondary ions, K⁺, cloud water pH, and atmospheric NOx. Additionally, 37 characteristic in‐cloud aqSOM molecules, classified as ‐Ox, ‐NOx, ‐N2Ox, and ‐N1‐2OxS, mainly consisting of dicarboxylic acids, nitrophenols, and dinitrophenols, were identified using linear discriminant analysis effect size (LefSe). The characteristic N‐ and S‐containing molecules in in‐cloud aqSOM with carbon numbers >10 had low or extremely low volatility; therefore, they might contribute to secondary organic aerosol formation after droplet evaporation. The results revealed the modifying effects of in‐cloud processes on aerosol organic composition at the molecular level and could improve our understanding of aerosol–cloud interactions.
... Raja et al., 2008;Straub et al., 2012;Salem et al., 2017). Besides, the DOCs at Cronenbourg and Strasbourg are also lower than those reported in Bakers eld(27 ppm) and Fresno (20 ppm). ...
Four sites representing urban (Strasbourg), suburban (Geispolsheim and Cronenbourg), and rural (Erstein) in the Alsace region, north east of France are sampled to investigate the evolution of the chemical composition of fog water between 2015 and 2021. For this aim, forty-two fog samples are collected using a Caltech Active Strand Cloud Collector (CASCC). The samples are analyzed for their inorganic species (metals and ions) and their physico-chemical properties (pH, dissolved organic carbon (DOC), liquid water content (LWC), and conductivity (K)). Temporal and spatial evolutions have been also investigated between the four sampling sites. Our results are then compared to previous studies performed in 1990’s at Strasbourg. Since 1999, there is a lack of fog knowledge in Strasbourg metropolitan and complete absence of fog studies. That’s why it is interesting to resume fogwater collection in order to re-build a solid background regarding air quality in France, particularly in Alsace, and assess the effectiveness of the rules and regulations that have been implemented over time.
... A solution composed of 0.1 mM GUA and 1 mM AN (GUA + AN) was also examined for comparison with GUA + DMB + AN and GUA + VL + AN. Sulfuric acid (H 2 SO 4 ; Acros Organics, ACS reagent, 95 % solution in water) was used to adjust the pH of the solutions to 4, which is within typical cloud pH values (2-7; Pye et al., 2020) and pH values observed in wood-burningimpacted cloud and fog waters (Collett et al., 1998;Raja et al., 2008). The solutions (initial volume of 500 mL) were bubbled with synthetic air (0.5 dm 3 min −1 ) for 30 min be-fore irradiation and throughout the reactions to achieve airsaturated conditions (Du et al., 2011;Chen et al., 2020) and were continuously magnetically stirred. ...
Aromatic carbonyls (e.g., methoxybenzaldehydes), an important class of photosensitizers, are abundant in the atmosphere. Photosensitization and nitrate-mediated photo-oxidation can occur simultaneously, yet studies about their interactions, particularly for aqueous secondary organic aerosol (aqSOA) formation, remain limited. This study compared non-phenolic (3,4-dimethoxybenzaldehyde, DMB) and phenolic (vanillin, VL) methoxybenzaldehydes as photosensitizers for aqSOA formation via guaiacol (GUA) oxidation in the absence and presence of ammonium nitrate (AN) under atmospherically relevant cloud and fog conditions. GUA oxidation by triplet excited states of DMB (3DMB∗) (GUA + DMB) was ∼ 4 times faster and exhibited greater light absorption than oxidation by 3VL∗ (GUA + VL). Both GUA + DMB and GUA + VL formed aqSOA composed of oligomers, functionalized monomers, oxygenated ring-opening species, and N-containing products in the presence of AN. The observation of N-heterocycles such as imidazoles indicates the participation of ammonium in the reactions. The majority of generated aqSOA comprises potential brown carbon (BrC) chromophores. Oligomerization and functionalization dominated in GUA + DMB and GUA + VL, but functionalization appeared to be more important in GUA + VL due to contributions from VL itself. AN did not significantly affect the oxidation kinetics, but it had distinct effects on the product distributions, likely due to differences in the photosensitizing abilities and structural features of DMB and VL. In particular, the more extensive fragmentation in GUA + DMB than in GUA + VL likely generated more N-containing products in GUA + DMB + AN. In GUA + VL + AN, the increased oligomers may be due to VL-derived phenoxy radicals induced by ⚫OH or ⚫NO2 from nitrate photolysis. Furthermore, increased nitrated products observed in the presence of both DMB or VL and AN than in AN alone imply that photosensitized reactions may promote nitration. This work demonstrates how the structural features of photosensitizers affect aqSOA formation via non-carbonyl phenol oxidation. Potential interactions between photosensitization and AN photolysis were also elucidated. These findings facilitate a better understanding of photosensitized aqSOA formation and highlight the importance of AN photolysis in these reactions.
... The quality of collected water is affected by air quality and particles that get stuck on the collecting mesh. Fog has been known to dissolve bicarbonates, calcium, sodium chloride (Klemm et al. 2012), heavy metal such as mercury (Ritchie et al. 2006), nitrates, organic carbon, and other ions (Raja et al. 2008) depending upon the concentration of the dissolved chemical species may affect the quality of collected water accordingly. ...
With the changing climate and environment, the nature of fog has also changed and because of its impact on humans and other systems, study of fog becomes essential. Hence, the study of its controlling factors such as the characteristics of condensation nuclei, microphysics, air–surface interaction, moisture, heat fluxes and synoptic conditions also become crucial, along with research in the field of prediction and detection. The current review expands for the period between 1976 to 2021, however, especially focused on the research articles published in the last two decades. It considers 250 research papers/research letters, 24 review papers, four book chapters/manuals, five news articles, 15 reports, six conference papers and five other online readings. This review is a compilation of the pros and cons of the techniques used to determine the factors influencing fog formation, its classification, tools and techniques available for its detection and forecast. Some recent advanced are also discussed in this review: role of soil properties on fogs, application of microwave communication links in the detection of fog, new class of smog, and how the cognitive abilities of humans are affected by fog. Recently India and China are facing an emergence and repetitions of fog haze/smog and thus their policies initiatives are also briefly discussed. It is concluded that the complexity in fog forecasting is high due to multiple factors playing a role at multiple levels. Most of the researchers have worked upon the role of humidity, temperature, wind, and boundary layer to predict fogs. However, the role of global wind circulations, soil properties, and anthropogenic heat requires further investigations. Literature shows that fog is being harnessed to address water insecurity in various countries, however, coastal areas of Angola, Namibia and South Africa, Kenya, Eastern Yemen, Oman, China, India, Sri Lanka, Mexico, along with the mountainous regions of Peru, Chile, and Ecuador, are some of the potential sites that can benefit from the installation of fog water harvesting systems.
... Unlike the large droplets in Stage_1, the TIC in the small droplets in Stage_2 and Stage_3 is high, indicating that the small droplets are enriched with chemical components. The size-dependent distribution characteristics of the chemical components in fog water have been reported by many studies Collett Jr. et al., 1999;Raja et al., 2008;Zhang et al., 2019). The mechanism is related to the aerosol activation process, gas absorption after fog-droplet formation, and liquid-phase chemical reaction (Lu et al., 2010b;Hu et al., 2019). ...
We conducted a three-month field experiment focusing on the physical and chemical characteristics of fog in a tropical rainforest in Xishuangbanna, Southwest China, in the winter of 2019. In general, the fog would form at midnight and persist because of the increased long-wave radiative cooling combined with the high relative humidity, gentle breeze, and a relatively low aerosol number concentration in the forest; the fog would dissipate before noon due to the increasing turbulence near the surface. This diurnal cycle is typical for radiation fog. The microphysical fog properties included a relatively low number concentration of the fog droplet, large droplet size, high liquid water content, narrow droplet number-size distribution, and high supersaturation. The chemical properties showed that the fog water was slightly alkaline with low electrical conductivity, whereas the highest proportions of anions and cations therein were Cl− and Ca2+, respectively; the chemical components were enriched in small fog droplets. In addition, we indirectly calculated the fog supersaturation according to the κ-Köhler theory. We found that condensation broadens the droplet number-size distribution at relatively low supersaturation, which is positively correlated with the fog-droplet number concentration and negatively correlated with the droplet mean-volume diameter; this affects the key microphysical processes of fog.
... The oxidation of organic compounds leads, in general, to carboxylic acids and proceeds through αor β-hydroxy acid to esters or oligoesters, similarly to the proposed mechanisms for oligomers in the aerosol phase (Gao et al., 2004;Tolocka et al., 2004;Surratt et al., 2006bSurratt et al., , 2007a. Since then, ester formation by the oxidation of organic matter in the troposphere has been the subject of many laboratory investigations (Hamilton et al., 2006;Surratt et al., 2006a;Szmigielski et al., 2007;Altieri et al., 2008;Galloway et al., 2009;Zhang et al., 2011;Kristensen et al., 2013;Strollo and Ziemann, 2013;Claflin and Ziemann, 2019;Mekic et al., 2019) and field studies (Raja et al., 2008(Raja et al., , 2009Kristensen et al., 2013). The work from suggested that esterification by the condensation of carboxylic acids with hydroxyl-group-containing molecules is not effi-cient enough to explain the oligoesters under realistic aerosol acidities. ...
The acidity of aqueous atmospheric solutions is a key parameter driving both the partitioning of semi-volatile acidic and basic trace gases and their aqueous-phase chemistry. In addition, the acidity of atmospheric aqueous phases, e.g., deliquesced aerosol particles, cloud, and fog droplets, is also dictated by aqueous-phase chemistry. These feedbacks between acidity and chemistry have crucial implications for the tropospheric lifetime of air pollutants, atmospheric composition, deposition to terrestrial and oceanic ecosystems, visibility, climate, and human health. Atmospheric research has made substantial progress in understanding feedbacks between acidity and multiphase chemistry during recent decades. This paper reviews the current state of knowledge on these feedbacks with a focus on aerosol and cloud systems, which involve both inorganic and organic aqueous-phase chemistry. Here, we describe the impacts of acidity on the phase partitioning of acidic and basic gases and buffering phenomena. Next, we review feedbacks of different acidity regimes on key chemical reaction mechanisms and kinetics, as well as uncertainties and chemical subsystems with incomplete information. Finally, we discuss atmospheric implications and highlight the need for future investigations, particularly with respect to reducing emissions of key acid precursors in a changing world, and the need for advancements in field and laboratory measurements and model tools.
... The acidity and ion concentration of small droplets are typically higher than those of large droplets (Collett et al., 1994Hoag et al., 1999). It is also significantly different between the chemical compositions in droplets with different sizes Menon et al. (2000); sulfate, nitrate, and ammonium typically enriched in small droplets (4-16 μm) Raja et al., 2008). Degefie et al. (2015) inferred a higher concentration of nitrate in large droplets but a higher concentration of sulfate in small droplets by combining fog microphysics with the chemical components of fog water. ...
The chemical characteristics of fog water are closely related to the droplet size. This study used a three-stage Caltech Active Strand Cloud Collector (CASCC) to collect 170 size-resolved fog samples from eight fog events in the winter of 2013–2017 at an urban site in Nanjing and the summit of Mt. Lu. The pH, electrical conductivity (EC), and inorganic ion concentration were analyzed, and the sources of pollutants in size-dependent droplets were discussed according to the local emission source type. The pH, EC, total ion concentration (TIC), and ion composition of fog water at Nanjing were dependent on the droplet size. The TIC of fog water at Nanjing was approximately 10 times that measured at Mt. Lu. The concentration of different chemical species in the droplet was also size-dependent: Ca²⁺ concentration was higher in larger droplets with the diameter (D) ≥ 22 μm, whereas SO4²⁻, NO3⁻, and NH4⁺ concentrations were higher in smaller droplets with D ranging 4–16 μm. The ion concentration of fog water at Mt. Lu first decreased then increased as the fog developed. Owing to the faster drop rate of larger droplets, coarse particles (2.5–10 μm) exhibited a faster response to fog removal, and the final mass concentration of fine particles (< 2.5 μm) decreased the most due to competition between deposition and gravity. Different pollution sources exhibited different contribution rates to the chemical components of size-dependent droplets. Soil sources mainly affected the Ca²⁺ content of large droplets, whereas industrial sources and vehicles affected the NO3⁻ and SO4²⁻ concentrations of medium and small droplets. Soil sources, industrial sources, and vehicles were the main sources of fog water at the urban site in Nanjing, whereas industrial sources, vehicles, soil sources, biomass combustion, and secondary aerosols were the main sources of fog water at the summit of Mt. Lu.
... The oxidation leads to carboxylic acids and proceeds through α-or β-hydroxy acid to esters or oligoesters, similarly to the proposed mechanisms for oligomers in the aerosol phase (Gao et al., 2004;Tolocka et al., 2004;Surratt et al., 2006a;Surratt et al., 2007a). Since then, ester formation by oxidation of organic matter in the troposphere has been the subject of many laboratory investigations (Hamilton et al., 2006;Surratt et al., 2006b;975 Szmigielski et al., 2007;Altieri et al., 2008;Galloway et al., 2009;Zhang et al., 2011;Birdsall et al., 2013;Kristensen et al., 2013;Strollo and Ziemann, 2013;Claflin and Ziemann, 2019;Mekic et al., 2019) and field studies (Raja et al., 2008;Raja et al., 2009;Kristensen et al., 2013). The work from (Birdsall et al., 2013) suggested that esterification by condensation of carboxylic acids with hydroxyl group containing molecules is not efficient enough to explain the oligoesters under realistic aerosol acidities. ...
The acidity of aqueous atmospheric solutions is a key parameter driving both the partitioning of semi-volatile acidic and basic trace gases and their aqueous-phase chemistry. In addition, the acidity of atmospheric aqueous phases, e.g. deliquesced aerosol particles, cloud and fog droplets, is also dictated by aqueous-phase chemistry. These feedbacks between acidity and chemistry have crucial implications for the tropospheric lifetime of air pollutants, atmospheric composition, deposition to terrestrial and oceanic ecosystems, visibility, climate, and human health. Atmospheric research has made substantial progress in understanding feedbacks between acidity and multiphase chemistry during recent decades. This paper reviews the current state of knowledge on these feedbacks with a focus on aerosol and cloud systems, involving both inorganic and organic aqueous-phase chemistry. Here, we describe the impacts of acidity on the phase partitioning of acidic and basic gases and buffering phenomena. Next, we review feedbacks of different acidity regimes on key chemical reaction mechanisms and kinetics, as well as uncertainties and chemical subsystems with incomplete information. Finally, we discuss atmospheric implications and highlight needs for future investigations, particularly with respect to reducing emissions of key acid precursors in a changing world, and needs for advancements of field and laboratory measurements and model tools.
... It was found that in the urban areas fog could be affected by the presence of industries" emissions, as higher levels of particles and heavy metals are found in the fog of those areas [14]. The ability to absorb toxins disposed on the air proved to be higher in urban areas compared to rural areas, as the fog in urban areas exhibit higher levels of total organic carbon, nitrate and sodium and as a result have a lower PH level [15]. ...
Fog harvesting is a technique used to collect water from the fog. This technique became widely used around the world due to the lack of fresh water, as fog harvesting is considered to represent an economical and a reliable source of water. On that sense, fog collecting methods are mostly implemented in areas that lack access to fresh water and is mostly used for agricultural purposes and, in some cases, also for providing clean drinking water. The basic idea of harvesting the fog was first developed by farmers when some types of adjoining cavities and containers were put around plants to collect water from humid air, after that those techniques were turned into fog harvesting structures. The introduction of fog harvesting techniques was accompanied with the introduction of new materials and different structures, providing a range of options in regards to the meshes and to the harvesting methods. In this paper, a practical and theoretical assessment of existing fog harvesting meshes is performed in order to characterize their economic and physical characteristics. The final objective is to provide information about their ability to perform in different conditions which is to be added to an environmental conditioning structure for exterior spaces.
... In the same way, * need to be estimated. For that, DOC measurements for the various cloud events are available (see in Table III constituting about 80% of the total organic carbon in the aqueous phase (Raja et al., 2008;Straub et al., 2012). For the calculation, we consider a value for * based on DOC measurements where we recalculate a TOC value (DOC/TOC = 90%) and we consider that 10% of TOC is insoluble. ...
Volatile Organic Compounds (VOC), including saturated, unsaturated, and other substituted hydrocarbons, play a major role in atmospheric chemistry. They are primarily emitted by anthropogenic and biogenic sources into the atmosphere; they are also transformed in situ by chemical reactions, and more specifically, by photo-oxidation leading to the formation of ozone (O3) and Secondary Organic Aerosol (SOA). By altering the organic fraction of aerosol particles, VOC modify the Earth’s radiative balance through a direct effect (absorption and scattering of solar radiation) or through indirect effect by altering cloud microphysical properties. They also present a direct effect on human health and on the environment.During their atmospheric transport, VOC and their oxidation products, Oxygenated Volatile Organic Compounds (OVOC), may partition between the gaseous and aqueous phases depending on their solubility. Clouds have a significant effect on tropospheric chemistry by redistributing trace constituents between phases and by providing liquid water in which aqueous phase chemistry can take place. Indeed, during the cloud lifetime, chemical compounds and particularly VOC are efficiently transformed since clouds favor the development of complex “multiphase chemistry”. The latter presents several particularities. First, photochemical processes inside the droplets are important in the transformation of chemical compounds. Second, aqueous chemical reactions are efficient and can be faster than the equivalent reactions in the gas phase. This can be related to the presence of strong oxidants such as hydrogen peroxide H2O2 or Transition Metal Ions (TMI), which participate in the formation of radicals such as hydroxyl radicals (HO•) that favor oxidation processes. Furthermore, the presence of viable microorganisms has been highlighted and shown to participate in transformations of the chemical species. Finally, these transformations in clouds are also strongly perturbed by microphysical processes that control formation, lifetime and dissipation of clouds. These processes will redistribute the chemical species between the different reservoirs (cloud water, rain, particle phase, gaseous phase, and solid ice phase). In this frame, the transformation of VOC in the cloud medium can lead to the production of secondary compounds contributing to SOA formation, reported as “cloud aqSOA”. This secondary organic aerosol mass produced during the cloud lifetime could explain in part the ubiquity of small dicarboxylic and keto acids and high molecular-weight compounds measured in aerosol particles, fog water, cloud water, or rainwater at many locations, as they have neither substantial direct emission sources nor any identified important source in the gas phase. This aqSOA mass stays in the particle phase after cloud evaporation implying a modification of the (micro)physical and chemical properties of aerosol particles (particle size, chemical composition, morphology). This leads to modifications of their impacts on consecutive cloud or fog cycles (aerosol indirect effects) and of their interactions with incoming radiation by scattering/absorbing (aerosol direct effect). (...)
... The ratio of Cl − /Na + was lower in the sea fog (0.78) than in the sea water (1.17), which, as reported in Keene et al. 1986;Collett et al. 2002, can arise from depletion of Cl − due to HCl volatilization from sea-salt particles (Table 2). Sea salt particles can be acidified via HNO 3 and/or H 2 SO 4 uptake or production and then act as sea fog condensation nuclei (Andreae and Crutzen 1997;Raja et al. 2008;Jung et al. 2013). In contrast, the ratio of Cl − /Na + was slightly higher in the rain than in the sea water. ...
Clouds, fogs, and rain can serve as useful integrators of both atmospheric aerosols and soluble trace gases. To better understand the chemical characteristics of sea fog and rain in the North and South Pacific Ocean, fog and rain were measured aboard the R/V ARAON in 2012 and 2014, respectively, as part of the Ship-borne Pole-to-Pole Observations (SHIPPO) project. The mean sea fog pH (3.59) was lower than the mean rain pH (4.54), reflecting greater inputs of non-sea-salt (nss)-SO42−. For the collected rain, nss-Ca2+ and nss-Mg2+ from mineral dust particles were the major contributors to acidity neutralization. NO3− concentrations, which are derived from scavenging of gaseous nitric acid and aerosol nitrate, were higher than NH4+ concentrations, indicating that terrestrial and/or local anthropogenic NO3− sources outweighed contributions from anthropogenic or biological oceanic NH3/NH4+ sources. The ratio of Cl−/Na+ in the sea fog was slightly lower than that in the sea water due to HCl volatilization from scavenged sea-salt particles. The ratio of NH4+/ nss-Ca2+ was lower in the rain than in the sea fog, revealing the influence of mineral dust particles at altitudes above the sea fog layer. The average sea fog water TOC concentration, 13.2 ppmC, was much higher than the measured TOC concentrations in marine fogs and clouds in other remote environments, likely due to continental influence; the TN and TOC concentrations in the fog water were much higher than those in the rain. The sea fog and rain chemical properties measured during research cruises like these enhance our understanding of wet deposition and cloud condensation nuclei sources and processes in the Pacific Ocean.
... During nonhaze days, MSA was probably mainly formed via secondary pathway because of the moderate correlations only with nss-SO 4 2− , NO 3 − , and NH 4 + (R 2 = 0.51, 0.40, 0.40). Lactic acid is mainly derived from biological source such as lactobacillus (Cabredo et al. 2009) and plant tissues (Raja et al. 2008), and it can also be produced by the reactions of ozone and isoprene (Nguyen et al. 2010). In Category 1, lactic acid had nothing correlated well. ...
... It was found metals are found in the fog of those areas (D.Ritchie, Richards and A.Arp 2006). The ability to absorb toxins disposed on the air proved to be higher in urban areas compared to rural areas, as the fog in urban areas exhibit higher levels of total organic carbon, nitrate and sodium and as a result have a lower PH level (Raja, et al. 2008). ...
As fresh water becomes scarce nowadays, fog harvesting appeared as a new opportunity to be considered as an economical and a reliable fresh water source. Thus Fog collectors represent a functional solution to provide fresh water to be used in agriculture and in some cases, also as drinking water. Fog harvesting techniques had been used first by farmers as some types of adjoining cavities and containers were added around plants to take advantage of the humid weather, after that, these techniques were turned into structures. With fog harvesting techniques emerging, new materials and new structures are being developed, providing a range of options in regards to the meshes and to the harvesting methods. In this paper, Fog harvesting meshes are reviewed and analysed to process its ability on providing environmental conditioning of exterior spaces. The purpose of such tests is to acquire a new understanding and provide other options for fog harvesting materials while taking into consideration the economic and environmental aspects of each material used.
... The three-stage CASCC is a size-fractionating cloud water collector for droplet diameters from approximately 22 μm (stage one), 16 μm (stage two) and 4 μm (stage three) droplet diameter at a volume flow rate of 19 m 3 min −1 associated with theoretical 50% size cuts (Raja et al., 2008). Similarly, cloud droplets are drawn by a fan via a duct and are collected relying on impact. ...
Summertime bulk and size-segregated cloud water samples were collected in 2014 at the summit of Mount Tai (Mt. Tai, 1534 m a.s.l.) in the North China Plain to investigate the concentrations, size distributions and stable carbon isotopic compositions (δ¹³C) of dicarboxylic acids, oxoacids and α-dicarbonyls as well as fluorescence properties of dissolved organic carbon (DOC). Positive correlations were observed for Peaks A (terrestrial humic-like), M (marine humic-like) and T (protein-like) with diacids and related compounds (r² ≥ 0.43), except for Peak M and α-dicarbonyls, illustrating that fluorescent components and dicarboxylic acids were derived from common biological origins and biomass burning. Oxalic acid (C2, 2080 μg L⁻¹) was the dominant diacid in this study, followed by succinic (C4, 640 μg L⁻¹) and glyoxylic (ωC2, 448 μg L⁻¹) acids. Compared to organic precursors, the relatively negative δ¹³C values of C2 (−18.8‰), glyoxylic acid (ωC2, –16.6‰), pyruvic acid (Pyr, −21.5‰) and methylglyoxal (MeGly, −19.6‰) supported that C2, Pyr, ωC2 and MeGly were formed via the oxidation of ¹³C-enriched organic precursors in aqueous phase. Furthermore, the larger size (22 μm) of cloud droplet was associated with more abundant organic compounds in general, which might be caused by scavenging ability and condensation of aerosol particles on the larger surface of large droplets. Our study suggested that high loadings of diacids and related compounds in cloud water over Mt. Tai were involved with emissions from anthropogenic and biological sources, followed by photochemical formation during the long-range atmospheric transport.
... Lactic acid is produced by lactobacillus (Cabredo et al., 2009), which is known to exist in soil (Huysman and Verstraete, 1993) and emitted from plant tissues in agricultural farm (primary origin) (Raja et al., 2008). This organic acid can also be produced by the oxidation of isoprene with ozone (Nguyen et al., 2010) (secondary origin). ...
To understand the source and atmospheric behaviour of low molecular weight monocarboxylic acids (monoacids), gaseous (G) and particulate (P) organic acids were collected at the summit of Mt. Tai in the North China Plain (NCP) during field burning of agricultural waste (wheat straw). Particulate organic acids were collected with neutral quartz filter whereas gaseous organic acids were collected with KOH-impregnated quartz filter. Normal (C1-C10), branched (iC4-iC6), hydroxy (lactic and glycolic), and aromatic (benzoic) monoacids were determined with a capillary gas chromatography employing p-bromophenacyl esters. We found acetic acid as the most abundant gas-phase species whereas formic acid is the dominant particle-phase species. Concentrations of formic (G/P 1 570/1 410 ng m⁻³) and acetic (3 960/1 120 ng m⁻³) acids significantly increased during the enhanced field burning of agricultural wastes. Concentrations of formic and acetic acids in daytime were found to increase in both G and P phases with those of K⁺, a field-burning tracer (r = 0.32–0.64). Primary emission and secondary formation of acetic acid is linked with field burning of agricultural wastes. In addition, we found that particle-phase fractions (Fp = P/(G + P)) of formic (0.50) and acetic (0.31) acids are significantly high, indicating that semi-volatile organic acids largely exist as particles. Field burning of agricultural wastes may play an important role in the formation of particulate monoacids in the NCP. High levels (917 ng m⁻³) of particle-phase lactic acid, which is characteristic of microorganisms, suggest that microbial activity associated with terrestrial ecosystem significantly contributes to the formation of organic aerosols.
... In this study, concentrations of benzoic acid in the IGP-outflow (0.3 ± 0.1 ng m À3 ) overlap with the SEA-outflow (0.3 ± 0.2 ng m À3 ). On the other hand, lactic acid is primarily produced by soil microbial activities (Huysman and Verstraete, 1993) and from the plant tissues (Raja et al., 2008). Lactic acid can also be formed secondarily by the oxidation of isoprene with ozone (Nguyen et al., 2010). ...
Low molecular weight monocarboxylic acids (LMW monoacids) are most abundant volatile organic compounds (VOCs) in the atmosphere and often act as important contributors to the acidity of precipitation in addition to inorganic acids. However, there is a large uncertainty in the sources and secondary formations of these acids in the atmosphere. This study reports homologous series of LMW monoacids, including normal (C1-C10), branched chain (iC4-iC6), aromatic (benzoic acid) and hydroxyacids (lactic and glycolic acids) in the fine-mode (PM2.5) aerosols collected over the Bay of Bengal (BoB) during a winter cruise (December 2008 to January 2009). The samples were associated with two distinct continental air masses arriving from the Indo-Gangetic Plain (IGP-outflow) and Southeast Asia (SEA-outflow). The molecular distributions of organic acids are characterized by the dominance of formic acid (C1) followed by acetic acid (C2) and nonanoic acid (C9) in the IGP-outflow, whereas dominance of C1 or C9 was observed in the SEA-outflow followed by C1. Formic-to-acetic acid (C1/C2) ratios were higher than unity (mean: 1.3 ± 0.3) in the IGP-outflow, whereas they were less than unity (0.9 ± 0.5) in the SEA-outflow. These results suggest that secondary formation of organic acids is largely important in the IGP-outflow whereas primary emission is a major source of organic acids in the SEA-outflow. Based on the correlation coefficient matrix analysis and C1/C2 and C4/C3 ratios, we consider that the sources of C1 are probably associated with the secondary formation via the oxidation of biogenic VOCs, while C2 has both primary and secondary formations associated with anthropogenic sources in the IGP-outflow. On the other hand, C1 and C2 have similar sources (both primary and secondary) originated from biomass burning and bacterial activities via long-range atmospheric transport in the SEA-outflow, as inferred from the MODIS fire spot data, significant concentrations of isovaleric acid (iC5), and a significant correlation (r = 0.67) between nss-K⁺ and total LMW monoacids.
... The highest DOC values in Whistler (∼ 10 mgC L −1 ) are higher than the average values in the more anthropogenically-impacted locations possibly because of stronger biogenic organic carbon sources in Whistler. In general, it has been found that DOC constitutes about 80 % of the total organic carbon (TOC) in the aqueous phase (Herckes et al., 2002a;Raja et al., 2008;Straub et al., 2012); thus, DOC is a nearly quantitative measure of TOC in the condensed phase of clouds and fogs. ...
Cloud and fog droplets efficiently scavenge and process water-soluble compounds and, thus, modify the chemical composition of the gas and particle phases. The concentrations of dissolved organic carbon (DOC) in the aqueous phase reach concentrations on the order of ~ 10 mgC L−1 which is typically on the same order of magnitude as the sum of inorganic anions. Aldehydes and carboxylic acids typically comprise a large fraction of DOC because of their high solubility. The dissolution of species in the aqueous phase can lead to (i) the removal of species from the gas phase preventing their processing by gas phase reactions (e.g., photolysis of aldehydes) and (ii) the formation of unique products that do not have any efficient gas phase sources (e.g., dicarboxylic acids). We present measurements of DOC and select aldehydes in fog water at high elevation and intercepted clouds at a biogenically-impacted location (Whistler, Canada) and in fog water in a more polluted area (Davis, CA). Concentrations of formaldehyde, glyoxal and methylglyoxal were in the micromolar range and comprised ≤ 2% each individually of the DOC. Comparison of the DOC and aldehyde concentrations to those at other locations shows good agreement and reveals highest levels for both in anthropogenically impacted regions. Based on this overview, we conclude that the fraction of organic carbon (dissolved and insoluble inclusions) in the aqueous phase of clouds or fogs, respectively, comprises 2–~ 40% of total organic carbon. Higher values are observed to be associated with aged air masses where organics are expected to be more highly oxidised and, thus, more soluble. Accordingly, the aqueous/gas partitioning ratio expressed here as an effective Henry's law constant for DOC (KH*DOC) increases by an order of magnitude from 7 × 103 M atm−1 to 7 × 104 M atm−1 during the ageing of air masses. The measurements are accompanied by photochemical box model simulations. These simulations are used to contrast two scenarios, i.e., an anthropogenically vs. a more biogenically impacted one as being representative for Davis and Whistler, respectively. Since the simplicity of the box model prevents a fully quantitative prediction of the observed aldehyde concentrations, we rather use the model results to compare trends in aldehyde partitioning and ratios. They suggest that the scavenging of aldehydes by the aqueous phase can reduce HO2 gas phase levels significantly by two orders of magnitude due to a weaker net source of HO2 production from aldehyde photolysis in the gas phase. Despite the high solubility of dicarbonyl compounds (glyoxal, methylglyoxal), their impact on the HO2 budget by scavenging is < 10% of that of formaldehyde. The overview of DOC and aldehyde measurements presented here reveals that clouds and fogs can be efficient sinks for organics, with increasing importance in aged air masses. Even though aldehydes, specifically formaldehyde, only comprise ~ 1% of DOC, their scavenging and processing in the aqueous phase might translate into significant effects in the oxidation capacity of the atmosphere.
... As will be further discussed below, due to the utilization of the stainless steel collector, high blanks of some trace metals were observed. For sizeresolved cloud water collection, a three-stage plastic CASCC (Raja et al., 2008) cloud water collector with nominal cloud droplet cutoffs (50 % lower cut size specified as drop diameter) at 4, 16, and 22 µm was used. Bulk cloud water samples were collected every hour, while size-resolved samples were taken at a 2 h time resolution during cloud events. ...
Trace metal characterization of bulk and size-resolved aerosol and cloud
water samples were performed during the Hill Cap Cloud Thuringia (HCCT)
campaign. Cloud water was collected at the top of Mt. Schmücke while
aerosol samples were collected at two stations upwind and downwind of Mt.
Schmücke. Fourteen trace metals including Ti, V, Fe, Mn, Co, Zn, Ni, Cu,
As, Sr, Rb, Pb, Cr, and Se were investigated during four full cloud events
(FCEs) that fulfilled the conditions of a continuous air mass flow through the
three stations. Aerosol particle trace metal concentrations were found to be
lower than those observed in the same region during previous field
experiments but were within a similar range to those observed in other rural
regions in Europe. Fe and Zn were the most abundant elements with
concentration ranges of 0.2–111.6 and
1.1–32.1 ng m−3,
respectively. Fe, Mn, and Ti were mainly found in coarse mode aerosols while
Zn, Pb, and As were mostly found in the fine mode. Correlation and enrichment
factor analysis of trace metals revealed that trace metals such as Ti and Rb
were mostly of crustal origin while trace metals such as Zn, Pb, As, Cr, Ni,
V, and Cu were of anthropogenic origin. Trace metals such as Fe and Mn were of
mixed origins including crustal and combustion sources. Trace metal cloud
water concentration decreased from Ti, Mn, Cr, to Co with average
concentrations of 9.18, 5.59, 5.54, and 0.46 μg L−1,
respectively. A non-uniform distribution of soluble Fe, Cu, and Mn was
observed across the cloud drop sizes. Soluble Fe and Cu were found mainly in
cloud droplets with diameters between 16 and 22 μm, while Mn was
found mostly in larger drops greater than 22 μm. Fe(III) was the
main form of soluble Fe especially in the small and larger drops with
concentrations ranging from 2.2 to
37.1 μg L−1. In
contrast to other studies, Fe(II) was observed mainly in the evening hours,
implying its presence was not directly related to photochemical processes.
Aerosol–cloud interaction did not lead to a marked increase in soluble trace
metal concentrations; rather it led to differences in the chemical composition of
the aerosol due to preferential loss of aerosol particles through physical
processes including cloud drop deposition to vegetative surfaces.
... We ran the CASCC with a volume flow of 19 m 3 min −1 . Based on modeling results presented by Raja et al. (2008), the expected 50 % size cuts for stage one, two and three were approximately 22, 16 and 4 µm, respectively. The term 50 % size cut corresponds to the droplet size at which droplets are collected with a 50 % efficiency; larger droplets are collected with a higher and smaller droplets with a smaller efficiency. ...
In this work, we present the first observations of stable water isotopologue ratios in cloud droplets of different sizes collected simultaneously. We address the question whether the isotope ratio of droplets in a cloud varies as a function of droplet size. Samples were collected from a ground intercepted cloud (=fog) during the Hill Cap Cloud Thuringia 2010 campaign (HCCT-2010) using a three-stage Caltech Active Strand Cloud water Collector (CASCC). An instrument test revealed that no artificial isotopic fractionation occurs during sample collection with the CASCC. Furthermore, we could experimentally confirm the hypothesis that the δ values of cloud droplets of the relevant droplet sizes (μm-range) were not significantly different and thus can be assumed to be in isotopic equilibrium immediately with the surrounding water vapor. However, at the dissolution period of the cloud differences in isotope ratios of the different droplet sizes tended to be larger. This is likely to result from the cloud's heterogeneity, implying that larger and smaller cloud droplets have been collected at different moments in time, delivering isotope ratios from different collection times.
... Among WSOCs, monocarboxylic acids, dicarboxylic acids and ketocarboxylic acids are group of significant interest (Saxena and Hildemann, 1996;Falkovich et al., 2004). Carboxylic acids represent major fraction of organic carbon in fog, cloud water, precipitation, vapour phase and in particulate matter because of their solubility and polar nature (Keene and Galloway, 1984;Facchini et al., 1992;Khwaja, 1995;Kumar et al., 1996;Khare et al., 1997;Loflund et al., 2002;Fornaro and Gutz, 2003;Raja et al., 2008). The monocarboxylic acids (MCA), acetic acid (AA) and formic acid (FA) constitute the most abundant part of carboxylic acids in the global troposphere with a total quantity of 1200-1400 Gmol yr -1 (Paulot et al., 2011). ...
PM2.5 and PM10 aerosols from a semi-urban site of Agra (27°10′N, 78°05′E) in North-Central India were analyzed for carbonaceous aerosols (Organic and Elemental carbon), low molecular weight monocarboxylic acids (Acetic and Formic acid) along with inorganic ions (Cl⁻, NO3⁻, SO4²⁻, K⁺ and Ca²⁺) during April 2014 to August 2015. The average PM2.5 and PM10 mass concentrations were 86.3 ± 71.3 and 169.7 ± 100.5 µg m⁻³, respectively; about 45% of PM2.5 and 67% of PM10 samples were above NAAQ (National Ambient Air Quality) standards. The average organic carbon (OC) and elemental carbon (EC) concentrations were 18.2 ± 12.3 and 6.7 ± 4.5 µg m⁻³, respectively in PM2.5 and 25.2 ± 14.1 and 8.1 ± 5.9 µg m⁻³ respectively in PM10. The average concentration of acetic acid (AA) in PM2.5 and PM10 were 330 ± 211 and 392 ± 224 ng m⁻³ respectively. The average concentration of formic acid (FA) in PM2.5 and PM10 were 348 ± 193 and 336 ± 175 ng m⁻³ respectively. Formic acid concentration was higher in PM2.5 than PM10 but the difference is not statistically significant. Both AA and FA showed similar seasonal variation: winter > post-monsoon > summer > monsoon. Low temperature and high relative humidity in winter season favours gas to particle conversion resulting in high concentrations. The average FA to AA (F/A) ratio was 0.69 indicating dominance of primary sources at the study site. Correlation analysis of AA and FA with major ions (Cl⁻, NO3⁻, SO4²⁻, K⁺ and Ca²⁺), EC, secondary organic carbon and trace gases (O3 and CO) was performed to identify their primary or secondary origin. The results of correlation analysis suggest that AA is mainly contributed by primary sources while FA originates from secondary sources.
... The SO 4 2− concentrations of 2800− 41400 μeq L −1 observed during the haze-fog events in China were 1.6−21 times the values reported in the urban US. 35 Note that Strater et al. 34 did observe SO 4 2− concentrations in this range (7300 μeq L −1 ) but only during a single fog event. ...
In recent years in a few Chinese megacities, fog events lasting one to a few days have been frequently associated with high levels of aerosol loading characterized by high sulfate (as high as 30 µg m-3), therefore termed as haze-fog events. The concomitant pollution characteristics include high gas-phase mixing ratios of SO2 (up to 71 ppbv) and NO2 (up to 69 ppbv), high aqueous phase pH (5-6), and smaller fog droplets (as low as 2 µm), resulting from intense emissions from fossil fuel combustion and construction activities supplying abundant Ca2+. In this work, we use an observation-based model for secondary inorganic aerosols (OBM-SIA) to simulate sulfate formation pathways under conditions of haze-fog events encountered in Chinese megacities. The OBM analysis has identified, at a typical haze-fog water pH of 5.6, the most important pathway to be oxidation of S(IV) by dissolved NO2, followed by the heterogeneous reaction of SO2 on the aerosol surface. The aqueous phase oxidation of S(IV) by H2O2 is a very minor formation pathway as a result of the high NOx conditions suppressing H2O2 formation. The model results indicate that the unique cocktail of high fog water pH, high concentrations of NO2, SO2 and PM, and small fog droplets is capable of greatly enhancing sulfate formation. Such haze-fog conditions could lead to rapid sulfate production at night and subsequently high PM2.5 in the morning when the fog evaporates. Sulfate formation is simulated to be highly sensitive to fog water pH, PM and precursor gases NO2 and SO2. Such insights on major contributing factors imply that reduction of road dust and NOx emissions could lessen PM2.5 loadings in Chinese megacities during fog events.
... Strand Cloud Collector (CASCC)[Raja et al., 2008; Kaul et al., 2011] with 50% cut-off 130 diameters of 22 µm, 16 µm and 4 µm, respectively [Kaul et al., 2011] from the first to third 131 stages was used to collect droplet size resolved fog water samples. In this study stage cut-off 132 diameters are taken as diameters for coarse (C), medium (M) and fine (F) droplets. ...
Size-resolved fog water samples were collected in two consecutive winters at Kanpur, a heavily polluted urban area of India. Samples were analyzed by an aerosol mass spectrometer after drying and directly in other instruments. Residues of fine fog droplets (diameter: 4-16 μm) are found to be more enriched with oxidized (oxygen to carbon ratio, O/C = 0.88) and low volatility organics than residues of coarse (diameter > 22 μm) and medium size (diameter: 16-22 μm) droplets with O/C of 0.68 and 0.74, respectively. These O/C ratios are much higher than those observed for background ambient organic aerosols, indicating efficient oxidation in fog water. Accompanying box model simulations reveal that longer residence times, together with high aqueous OH concentrations in fine droplets, can explain these trends. High aqueous OH concentrations in smaller droplets are caused by their highest surface-volume ratio and high Fe and Cu concentrations, allowing more uptake of gas phase OH and enhanced Fenton reaction rates, respectively. Although some volatile organic species may have escaped during droplet evaporation, these findings indicate that aqueous processing of dissolved organics varies with droplet size. Therefore, large (regional, global)-scale models need to consider the variable reaction rates, together with metal-catalyzed radical formation throughout droplet populations for accurately predicting aqueous secondary organic aerosol formation.
Studies concerning fog water have been rapidly increasing due to its negative impacts on different environmental processes. However, fog water harvesting has become beneficial in various countries to overcome water scarcity. Accurate fog forecasting remains a challenging issue due to its spatio-temporal variability and uncertainties despite the development and efforts made to understand its chemistry and microphysics. The literature proved that the decrease in fog frequency over time in most countries is mainly attributed to the improvement in air quality or the change in regional climatic conditions. The current fog review summarizes its different types and collectors, life cycle, and impacts, the effects of aerosols, and the latest results concerning its forecast challenges and frequency. It also highlights the major chemical processes along with the main field studies performed on fog water. The aim of this work is not to provide a criticism about fog but to present a general comprehensive review of its physical and chemical aspects covering up to 330 research and review papers aimed to serve as a basis for new challenges and findings about fog water.
Aromatic carbonyls (e.g., methoxybenzaldehydes), an important class of photosensitizers, are abundant in the atmosphere. This study compared non-phenolic (3,4-dimethoxybenzaldehyde, DMB) and phenolic (vanillin, VL) methoxybenzaldehydes as photosensitizers for aqueous secondary organic aerosol (aqSOA) formation via guaiacol (GUA) oxidation under atmospherically relevant cloud and fog conditions. The effects of ammonium nitrate (AN) on these reactions were also explored. GUA oxidation by triplet excited states of DMB (3DMB*) (GUA+DMB) was ~4 times faster and exhibited greater light absorption than oxidation by 3VL* (GUA+VL). Both GUA+DMB and GUA+VL formed aqSOA composed of oligomers, functionalized monomers, oxygenated ring-opening species, and N-containing products in the presence of AN. The observation of N-heterocycles such as imidazoles indicates the participation of ammonium in the reactions. The majority of generated aqSOA are potential brown carbon (BrC) chromophores. Oligomerization and functionalization dominated in GUA+DMB and GUA+VL, but functionalization appeared to be more important in GUA+VL due to contributions from VL itself. AN did not significantly affect the oxidation kinetics, but it had distinct effects on the product distributions, likely due to differences in the photosensitizing abilities and structural features of DMB and VL. In particular, the more extensive fragmentation in GUA+DMB than in GUA+VL likely generated more N-containing products in GUA+DMB+AN. In GUA+VL+AN, the increased oligomers may be due to VL-derived phenoxy radicals induced by •OH or •NO2 from nitrate photolysis. Furthermore, increased nitrated products observed in the presence of both DMB or VL and AN than in AN alone implies that photosensitized reactions may promote nitration. This work demonstrates how the structural features of photosensitizers affect aqSOA formation via non-carbonyl phenol oxidation. Potential interactions between photosensitization and AN photolysis were also elucidated. These findings facilitate a better understanding of photosensitized aqSOA formation and highlight the importance of ammonium nitrate photolysis in these reactions.
Guaiacyl acetone (GA) is a phenolic carbonyl emitted in significant quantities by wood combustion that undergoes rapid aqueous-phase oxidation to produce aqueous secondary organic aerosol (aqSOA). We investigate the photosensitized oxidation of GA by an organic triplet excited state (3C*) and the formation and aging of the resulting aqSOA in wood smoke-influenced fog/cloud water. The chemical transformations of the aqSOA were characterized in situ using a high-resolution time-of-flight aerosol mass spectrometer. Additionally, aqSOA samples collected over different time periods were analyzed using high-performance liquid chromatography coupled with a photodiode array detector and a high-resolution Orbitrap mass spectrometer (HPLC-PDA-HRMS) to provide details on the molecular composition and optical properties of brown carbon (BrC) chromophores. Our results show efficient formation of aqSOA from GA, with an average mass yield around 80%. The composition and BrC properties of the aqSOA changed significantly over the course of reaction. Three generations of aqSOA products were identified via positive matrix factorization analysis of the aerosol mass spectrometry data. Oligomerization and functionalization dominated the production of the first-generation aqSOA, whereas fragmentation and ring-opening reactions controlled the formation of more oxidized second- and third-generation products. Significant formation of BrC was observed in the early stages of the photoreaction, while organic acids were produced throughout the experiment. High-molecular weight molecules (m/z > 180) with high aromaticity were identified via HPLC-PDA-HRMS and were found to account for a majority of the UV-vis absorption of the aqSOA.
With the objective of understanding fog water chemistry and sources contribution at an IGP outflow location (coastal Bhola Island, Bangladesh), we have collected fifteen fog water samples during winter 2016-17. Major ions, trace metals with physical properties (pH and electrical conductivity) were measured. The pH (7.12± 0.20) was slightly alkaline, which was much higher than rest of the world, but consistent with IGP region. Ca2+ containing species were the main contributor to the neutralization process of fog water, followed by K+ and Mg2+. The neutralizing species were derived mainly from soil dusts with a minor contribution from sea salt. HYSPLIT trajectory analysis revealed that substantial influences of the contaminated air mass in fog water from IGP. However, higher enrichment factors and parentage source contribution of SO42- (76.9), NO3- (99.3) and trace metals (Mn, Cu, and Zn) suggested significant anthropogenic contribution in the fog water at this Indo-Gangetic Outflow Location.
Cadmium is one of the non-essential and toxic heavy metals which affect the terrestrial and aquatic biota along with human beings due to its release from industrial effluents directly into terrestrial and aquatic ecosystem. The bioremediation of heavy metals using microorganisms has emerged as a substitute for the physicochemical techniques in recent years. So, the present study deals with the isolation and screening of heavy metal resistant bacteria from three different locations of battery manufacturing sites of Faridabad industrial area, Haryana, India. In this study, five bacterial isolates were selected based on high level of heavy metal resistance. Screening of the bacterial isolates for metal resistance against CdP2+P, NiP2+P, HgP2+P, CuP+2P and PbP2+ Pwas done by determining the minimal inhibitory concentration ranging from 10μg/ml to 250μg/ml. All the isolates were screened for their plasmid profile. The size of the isolated plasmid DNA was found to be more than 10,000bp. To determine whether the resistance gene was solely encoded by the plasmid, plasmid curing was done using ethidium bromide. The results showed that the bacterial growth on Cd-supplemented medium was not completely inhibited after plasmid curing, indicating the presence of multimechanisms involved in conferring resistance. It was observed that extracellular polymeric substances produced by isolates MF1 and MF2 play an important role in metal sorption and constitutes a passive method in which the metal cations bind to the negative charges of acidic groups from exopolysaccharide. In the remaining isolates, cadmium is precipitated as cadmium sulfide through hydrogen sulfide production. These heavy metal resistant organisms hold promise for bioremediation of heavy metal polluted environment
Keywords: Bioremediation, heavy metals, metal resistant bacteria, hydrogen sulfide, plasmid
The atmospheric aqueous-phase is a rich medium for chemical transformations of organic compounds, in part via photooxidants generated within the drops. Here we measure light absorption, photoformation rates and steady-state concentrations of two photooxidants – hydroxyl radical (•OH) and singlet molecular oxygen (¹O2*) – in 8 illuminated fog waters from Davis, California and Baton Rouge, Louisiana. Mass absorption coefficients for dissolved organic compounds (MACDOC) in the samples are large, with typical values of 10,000–15,000 cm² g-C⁻¹ at 300 nm, and absorption extends to wavelengths as long as 450–600 nm. While nitrite and nitrate together account for an average of only 1% of light absorption, they account for an average of 70% of •OH photoproduction. Mean •OH photoproduction rates in fogs at the two locations are very similar, with an overall mean of 1.2 (±0.7) μM h⁻¹ under Davis winter sunlight. The mean (±1σ) lifetime of •OH is 1.6 (±0.6) μs, likely controlled by dissolved organic compounds. Including calculated gas-to-drop partitioning of •OH, the average aqueous concentration of •OH is approximately 2 × 10⁻¹⁵ M (midday during Davis winter), with aqueous reactions providing approximately one-third of the hydroxyl radical source. At this concentration, calculated lifetimes of aqueous organics are on the order of 10 h for compounds with •OH rate constants of 1 × 10¹⁰ M⁻¹ s⁻¹ or higher (e.g., substituted phenols such as syringol (6.4 h) and guaiacol (8.4 h)), and on the order of 100 h for compounds with rate constants near 1 × 10⁹ M⁻¹ s⁻¹ (e.g., isoprene oxidation products such as glyoxal (152 h), glyoxylic acid (58 h), and pyruvic acid (239 h)). Steady-state concentrations of ¹O2* are approximately 100 times higher than those of •OH, in the range of (0.1–3.0) × 10⁻¹³ M. Since ¹O2* is a more selective oxidant than •OH, it will only react appreciably with electron-rich species such as dimethyl furan (lifetime of 2.0 h) and substituted polycyclic aromatic hydrocarbons (e.g., 9,10-dimethylbenz[a]anthracene with a lifetime of 0.7 h). Comparing our current Davis samples with Davis fogs collected in the late 1990s shows a decrease in dissolved organic carbon content, similar mass absorption coefficients, lower •OH concentrations, but very similar ¹O2* concentrations.
Cadmium is one of the non-essential and toxic heavy metals which affect the terrestrial and aquatic biota along with human beings due to its release from industrial effluents directly into terrestrial and aquatic ecosystem. The bioremediation of heavy metals using microorganisms has emerged as a substitute for the physicochemical techniques in recent years. So, the present study deals with the isolation and screening of heavy metal resistant bacteria from three different locations of battery manufacturing sites of Faridabad industrial area, Haryana, India. In this study, five bacterial isolates were selected based on high level of heavy metal resistance. Screening of the bacterial isolates for metal resistance against Cd²⁺, Ni²⁺, Hg²⁺, Cu²⁺ and Pb²⁺ was done by determining the minimal inhibitory concentration ranging from 10μg/ml to 250μg/ml. All the isolates were screened for their plasmid profile. The size of the isolated plasmid DNA was found to be more than 10,000bp. To determine whether the resistance gene was solely encoded by the plasmid, plasmid curing was done using ethidium bromide. The results showed that the bacterial growth on Cd-supplemented medium was not completely inhibited after plasmid curing, indicating the presence of multimechanisms involved in conferring resistance. It was observed that extracellular polymeric substances produced by isolates MF1 and MF2 play an important role in metal sorption and constitutes a passive method in which the metal cations bind to the negative charges of acidic groups from exopolysaccharide. In the remaining isolates, cadmium is precipitated as cadmium sulfide through hydrogen sulfide production. These heavy metal resistant organisms hold promise for bioremediation of heavy metal polluted environment.
The importance of the atmospheric aqueous phase of fogs and clouds, for the processing and removal of polycyclic aromatic hydrocarbons (PAHs) is not well known. A multiphase model was developed to determine the fate and lifetime of PAHs in fogs and clouds for a limited set of daytime conditions. The model describes partitioning between three phases (aqueous, liquid organic, and gas), experimental and estimated (photo)oxidation rates. Using a limited set of microphysical and chemical input conditions, the loss rates of PAHs in the complex three-phase system are explored.
Pinonic acid, a C10-monocarboxylic acid with a hydrophilic –CO2H group and a hydrophobic hydrocarbon backbone, is a key intermediate oxidation product of α-pinene – an important monoterpene compound in biogenic emission processes that influences the atmosphere. Molecular interaction between cis-pinonic acid and water is essential for understanding its role in the formation and growth of pinene-derived secondary organic aerosols. In this work, we studied the structures, energetics, and optical properties of hydrated clusters of the cis-pinonate anion (cPA⁻), the deprotonated form of cis-pinonic acid, by negative ion photoelectron spectroscopy and ab initio theoretical calculations. Our results show that cPA⁻ can adopt two different structural configurations – open and folded. In the absence of waters, the open configuration has the lowest energy and provides the best agreement with the experiment. The added waters, which mainly interact with the negatively charged –CO2⁻ group, gradually stabilize the folded configuration and lower its energy difference relative to the most stable open-configured structure. Thermochemical and equilibrium hydrate distribution analyses suggest that the mono- and di-hydrates are likely to exist in humid atmospheric environments with high populations. The detailed molecular description of cPA⁻ hydrated clusters unraveled in this study provides a valuable reference for understanding the initial nucleation process and aerosol formation involving organics containing both hydrophilic and hydrophobic groups, as well as for analyzing the optical properties of those organic aerosols.
Radiation fog samples have been collected at a rural site in Central Pennsylvania from 2007 through 2015 in order to document chemical composition, assess concentration changes over time, and to provide insight into emission sources that influence the region. The collection of samples over multiple years makes this one of the few long duration radiation fog studies that have been completed. During the course of the campaign, 146 samples were obtained and analyzed for pH, major inorganic ions, low molecular weight organic acids, total organic carbon (TOC) and total nitrogen (TN). Ammonium (median concentration = 209 μN), sulfate (69 μN), calcium (51 μN), and nitrate (31 μN) were the most abundant inorganic ions, although these were present at much lower concentrations than for radiation fog studies conducted in other locations. Organic acids, of which formate (20 μM) and acetate (21 μM) were the most abundant, were closer in magnitude to measurements made during previous studies. Organic acids accounted for 15% of TOC, which had a median concentration of 6.6 mgC l⁻¹. The median concentration of TN was 3.6 mgN l⁻¹, 18% of which was determined to be organic nitrogen. Statistically significant decreasing trends from 2007 to 2015 were noted for sulfate, ammonium, chloride, and nitrate. For the same period, an increase in pH was observed. Seasonal trends were identified for a number of species as well. The partitioning of ammonia between the gas and aqueous phases was also investigated and found to deviate significantly from equilibrium.
Aerosol, rainwater, and sea fog water samples were collected during the cruise conducted over the subarctic western North Pacific Ocean in the summer of 2008, in order to estimate dry, wet, and sea fog deposition fluxes of atmospheric inorganic nitrogen (N). During sea fog events, mean number densities of particles with diameters larger than 0.5 μm decreased by 12–78%, suggesting that particles with diameters larger than 0.5 μm could act preferentially as condensation nuclei (CN) for sea fog droplets. Mean concentrations of nitrate (NO<sub>3</sub><sup>−</sup>), methanesulfonic acid (MSA), and non sea-salt sulfate (nss-SO<sub>4</sub><sup>2−</sup>) in sea fog water were higher than those in rainwater, whereas those of ammonium (NH<sub>4</sub><sup>+</sup>) in both sea fog water and rainwater were similar. These results reveal that sea fog scavenged NO<sub>3</sub><sup>−</sup> and biogenic sulfur species more efficiently than rain. Mean dry, wet, and sea fog deposition fluxes for atmospheric total inorganic N (TIN; i.e. NH<sub>4</sub><sup>+</sup> + NO<sub>3</sub><sup>−</sup>) over the subarctic western North Pacific Ocean were estimated to be 4.9 μmol m<sup>−2</sup> d<sup>−1</sup>, 33 μmol m<sup>−2</sup> d<sup>−1</sup>, and 7.8 μmol m<sup>−2</sup> d<sup>−1</sup>, respectively. While NO<sub>3</sub><sup>−</sup> was the dominant inorganic N species in dry and sea fog deposition, inorganic N supplied to surface waters by wet deposition was predominantly by NH<sub>4</sub><sup>+</sup>. The contribution of dry, wet, and sea fog deposition to total deposition flux for TIN (46 μmol m<sup>−2</sup> d<sup>−1</sup>) were 11%, 72%, and 17%, respectively, suggesting that ignoring sea fog deposition would lead to underestimate of the total influx of atmospheric inorganic N into the subarctic western North Pacific Ocean, especially in summer periods.
In order to understand the chemical characteristics of fog water in Nanjing, three-stage Caltech Active Strand Cloud Collector (CASCC) was used to collect fog droplets in three separate droplet size ranges (from December 7th to December 9th. 2013). Fifty percent droplet size cuts of 22, 16, and 4 μm diameter are featured in stages one, two and three, respectively. Twenty-three fog samples were collected in two fog events and divided into eight periods. Concentrations of cations and anions in each sample were detected by ion chromatography. Composition of the fog water, chemical composition distribution characteristics of fog water in each stage, the correlation of ions in each stages and the relationship between ion concentrations and gaseous pollutants or microphysics were considered together during the analysis. The results showed the pH mostly resided in acidic range. The three-stage CASCC data showed significant size-dependence for all reported species. The small drop fraction had significantly high concentrations of the major ions (NH4+, NO3, SO442), lower pH values and higher EC values than the large drop fraction. Also the data showed concentrations of the species was higher at night. Due to the differences in contribution from regional pollutant sources, soluble components varied greatly in different fog events. Also the ionic composition had a significant relationship with microphysical properties and pollutant gases. ©, 2015, Zhongguo Huanjing Kexue/China Environmental Science. All right reserved.
Aldehydes and ketones, ubiquitous air, cloud, and fog water pollutants, are precursors to secondary organic aerosol formation and photochemical smog. Traditional aldehyde and ketone determination methods involve the addition of 2,4-dinitrophenylhydrazine (DNPH) as a derivatization agent, but many require a large sample volume or a lengthy extraction/concentration process. For fog water, where the sample size is inherently small, a DNPH derivatization method, based on U.S. EPA Method 8315A, was developed to combat this issue. In this method, a manual injection online concentration system in conjunction with HPLC was used, eliminating all liquid-liquid extraction and concentration steps and reducing the required sample volume. Hence, concentration and separation were combined in a single step. Using this injection method shortened the procedure time and also lowered the limit of detection to the nanomolar range. In this study, fourteen fog water samples, collected from October 2012 through April 2014 in Baton Rouge, LA, were analyzed for the concentration of aldehydes and ketones in order to test the feasibility of this method. Dissolved organic content (DOC), ionic concentration, and pH were measured. Formaldehyde, acetaldehyde, acrolein, butyraldehyde, benzaldehyde, and acetone were quantified. The DOC of the collected fog samples varied between 6.2 and 262.2 mgC/L. The wide range of organic content in the fog water samples corresponds to a diverse sample set, highlighted by the large variation of observed acetone concentration (under 5 nM to 1.05 mM). However, formaldehyde had a relatively stable concentration between each event (0.5 to 4.5 μM).
A new methodological approach is proposed to characterize aerosol water-soluble organic compounds (WSOC). Real aerosol and fog water samples were subjected to a procedure based on a combination of chromatographic separations, functional group investigation by proton nuclear magnetic resonance (HNMR), and total organic carbon determination. The complex mixture of aerosol/fog WSOC was separated by a chromatographic procedure into three main classes of compounds: (1) neutral/basic compounds; (2) mono- and di-carboxylic acids; (3) polyacidic compounds. Characterization by HNMR spectroscopy showed that fraction 1 is mainly composed of polyols or polyethers, fraction 2 is mainly composed of hydroxylated aliphatic acidic compounds, while fraction 3 is composed of highly unsaturated polyacidic compounds of predominantly aliphatic character, with a minor content of hydroxyl-groups. Quantitative data on the three classes of compounds were then derived from total organic carbon analysis, showing that the three separated fractions together account for 77% (in terms of C) of the total WSOC concentration of a fog water sample. Further quantitative information on the functional groups present in the three separated fractions can be obtained from HNMR spectra. This newly proposed approach to aerosol WSOC characterization provides comprehensive and synthetic information on aerosol organic composition which can be helpful for modeling purposes and is also particularly useful when aerosol chemical mass closure is pursued.
Analyses of fogwater collected by inertial impaction in the Los Angeles basin and the San Joaquin Valley indicated unusually high concentrations of major and minor ions. The dominant ions measured were NO3-, SO, 2-, NH, +, and H +. Nitrate exceeded sulfate on an equivalent basis by a factor of 2.5 in the central and coastal regions of the Los Angeles basin but was approximately equal in the eastern Los Angeles basin and the San Joaquin Valley. Maximum observed values for NH, +, NO3-, and SO, 2- were 10.0, 12.0, and 5.0, meq l- , while the lowest pH observed was 2.2. Iron and lead concentrations of over 0.1 mM and 0.01 mM, respectively, were observed. High concentrations of chemical components in fog appeared to correlate well with the occurrence of smog events. Concentrations in fogwater were also affected by the physical processes of condensation and evaporation. Light, dissipating fogs routinely showed the highest concentrations.
A method is described for the determination of volatile organic acids in the atmosphere, motor exhausts, and engine oils. Atmospheric organic acids were collected on a KOH impregnated quartz filter and derivatized to p-bromophenacyl esters. The derivatives were analyzed by high-resolution capillary gas chromatography and gas chromatography-mass spectrometry. Câ-Cââ aliphatic organic acids and benzoic acid were detected in Los Angeles air. Acetic and formic acids are dominant followed by propionic acids. Total concentrations measured were 0.37-7.45 ppb. Organic acids (Câ-Cââ) were also detected in the motor exhaust from a single automobile at idle conditions and showed that the distribution of individual acids was similar to that in the air, but the concentration was 17 times higher than for the average atmospheric content. Formic, acetic, and benzoic acids were detected as major species of used engine oil, but their content is negligible in new oil.
In many environments, organic compounds account for a significant fraction of fine particle mass. Because the lifetimes of accumulation mode aerosol particles are governed largely by interactions with clouds, it is important to understand how organic aerosol particles are processed by clouds and fogs. Clouds and fogs promote new particle mass formation (e.g., via rapid aqueous oxidation of sulfur dioxide to sulfate) and promote particle removal (e.g., via nucleation scavenging followed by direct drop deposition or drop incorporation into precipitation). Historically, most efforts have been directed toward understanding processing of inorganic species. Thus far we know little about cloud/fog processing of organic aerosol particles and trace gases. While a handful of compounds have received moderate attention (e.g., low molecular weight carboxylic acids), they form only a fraction of the multitude of organic compounds known to be present in the atmosphere.
Recently we have examined the organic composition of fogs and clouds in several environments, including locations in California, along the U.S. Gulf Coast, in Colorado, and in Hawaii. Observations of fog/cloud composition and processing of atmospheric organic matter are highlighted here.
Petrochemical industrial facilities can emit large amounts of highly reactive hydrocarbons and NOx to the atmosphere; in the summertime, such colocated emissions are shown to consistently result in rapid and efficient ozone (O-3) formation downwind. Airborne measurements show initial hydrocarbon reactivity in petrochemical source plumes in the Houston, TX, metropolitan area is primarily due to routine emissions of the alkenes propene and ethene. Reported emissions of these highly reactive compounds are substantially lower than emissions inferred from measurements in the plumes from these sources. Net O-3 formation rates and yields per NOx molecule oxidized in these petrochemical industrial source plumes are substantially higher than rates and yields observed in urban or rural power plant plumes. These observations suggest that reductions in reactive alkene emissions from petrochemical industrial sources are required to effectively address the most extreme O-3 exceedences in the Houston metropolitan area.
Low molecular weight dicarboxylic acids (Câ-Cââ) were analyzed in Los Angeles air and auto exhaust, as well as greenhouse air, soil, dust, and bog sediment samples, as dibutyl esters by gas chromatography and gas chromatography-mass spectrometry with fused silica capillary columns. In the Los Angeles ambient atmosphere, 19 dicarboxylic acids in the range Câ-Cââ were identified, including straight-chain, branched-chain, cis- and transunsaturated, and aromatic acids. Oxalic acid is the dominant species, followed by succinic, malonic, maleic, glutaric, adipic, and phthalic acids. Total concentration of Câ-Cââ diacids detected in the ambient atmosphere ranged from 5.5 to 21.2 nmol/m³ (average 12.2 +/- 6.1 nmol/mâ). By contrast, gasoline and diesel exhaust samples, collected under idling conditions, showed that distributions of the diacids are similar to those of air samples, but their concentrations are 28 (gasoline) and 144 (diesel) times higher than the average concentration of atmospheric diacids. These results indicate that engine exhaust is an important source of diaids in the urban atmosphere. 13 references, 3 figures. 1 table.
Results from the first study in Hong Kong, Southern China, to investigate the concentrations of organic acids in bulk deposition, aerosol and gas phase samples are presented. 57 daily bulk deposition samples were collected in central Kowloonand analyzed by ion chromatography, from May 1999 to May 2000. The volume-weighted (vw) mean concentrations for formate, acetate, propanoate and oxalate were 6.1, 4.5, 0.4 and 1.4 eq dm-3, respectively, with vw mean pH being 4.65.The maximum acidity contributions by formic and acetic acidsfor bulk deposition samples collected on a daily basis, withpH < 5.0,="" were="" 17="" and="" 14%,="" respectively.="" the="" concentrationsof="" these="" acids="" were="" significantly="" correlated="" with="" each="" other,="" butnot="" with="" ph.="" higher="" organic="" acid="" concentrations="" were="" foundin="" the="" dry,="" winter="" season,="" and="" for="" the="" synoptic="" weather="" systemtypes:="" approaching="" cyclone="" and="" cold="" front.="" oxalate="" levels="" weregenerally="" higher="" in="" bulk="" deposition="" samples="" for="" north/northeasterly="" air="" masses,="" higher="" surface="" windspeeds,="" and="" low="" rainfall="" amounts.="" formic="" and="" acetic="" acids="" were="" present="" at="" higher="" concentrations="" in="" the="" gas="" phase="" (mean="" concentrations="" at="" two="" sites="" were="" in="" the="" range="" from="" 3.2="" to="" 6.5="">g m-3, with formate usually < acetate),="" than="" in="" aerosols="" (mean="" concentration="" of="" formate,="" acetate="" or="" oxalate="">2.2 g m-3). Higher levels of organic acids both in aerosols and in the gas phase were found at a busy roadside site than at a residential site. Deposition fluxes for formic and acetic acidsare reported.
A chemical mass balance of fine aerosol (<1.5 μm AED) collected at three European sites was performed with reference to the water solubility of the different aerosol classes of components. The sampling sites are characterised by different pollution conditions and aerosol loading in the air. Aspvreten is a background site in central Sweden, K-puszta is a rural site in the Great Hungarian Plain and San Pietro Capofiume is located in the polluted Po Valley, northern Italy. The average fine aerosol mass concentration was 5.9 μg m-3 at the background site Aspvreten, 24 μg m-3 at the rural K-puszta and 38 μg m-3 at the polluted site San Pietro Capofiume. However, a similarly high soluble fraction of the aerosol (65–75%) was measured at the three sites, while the percentage of water soluble organic species with respect to the total soluble mass was much higher at the background site (ca. 50%) than at the other two sites (ca. 25%). A very high fraction (over 70%) of organic compounds in the aerosol consisted of polar species. The presence of water soluble macromolecular compounds was revealed in the samples from K-puszta and San Pietro Capofiume. At both sites these species accounted for between ca. 20–50% of the water soluble organic fraction. The origin of the compounds was tentatively attributed to biomass combustion.
The size dependency of fog droplet concentration and composition was studied using newly developed droplet impactors during the CHEMDROP campaign in the Po Valley (Italy). A strong size dependency of solute concentrations was measured during several fog episodes. The ionic strength of the droplet solutions varies as a function of droplet diameter, showing maximum values in the 9-19 μm diameter range. The solute concentration varies up to a factor of 10 among droplets of different diameter. Similarly, differences of up to 2 pH units are found among droplets of different diameter. The solute dependency of aerosol and droplets species from 0.1 μm to 50 μm is investigated. The monomodal behaviour of the solute concentration in droplets can be explained by both diffusional condensation of the aerosols serving as cloud condensation nuclei (CCN) and the air/liquid transfer of volatile species, in particular for HNO3 and NH3. The distribution of sulphur species is also size-dependent and is directly linked to the pH variations across the droplet spectrum, resulting in HMSA formation in small droplets and S(IV) oxidation large droplets.
Daily, seasonal, and spatial trends in fine particulate matter concentrations, compositions, and size distributions were examined using data collected through the regulatory fine particulate matter monitoring network in Southeast Texas and during the Gulf Coast Aerosol Research and Characterization Study (GC-ARCH or Houston Supersite). PM2.5 mass concentrations and compositions are generally spatially homogeneous throughout Southeast Texas when averaged over annual or seasonal time periods. There is relatively little seasonality to mean total PM2.5 mass and mean PM2.5 composition throughout the region, although slightly higher concentrations of total mass tend to occur in the spring and late fall. High FRM PM2.5 mass (>20 μg/m3) occurs both when there is high spatial variability among sites and low spatial variability among sites. This suggests that both local and regional emission sources contribute to PM2.5 in Southeast Texas. Sulfate ion (32%), organic carbon (30%), and ammonium ion (9%) are the largest components on average of PM2.5 by mass. Mean diurnal patterns for PM2.5 mass concentrations throughout the region show a consistent morning peak and a weaker and slightly less consistent peak in the late afternoon to early evening. High hourly averaged PM2.5 mass concentrations (>40 μg/m3) tend to be associated with daily average PM2.5 above the annual NAAQS of 15 μg/m3. These high hourly PM2.5 concentrations also tend to occur on days with high diurnal variation, indicative of elevated, short-lived PM 2.5 events. In contrast to mass concentrations, particle size distributions are not spatially homogeneous throughout Southeast Texas. Industrial sites have higher concentrations of freshly emitted, primary particles than more residential sites. Because the freshly emitted particles generally have diameters of 0.1 μm or less, these primary emissions do not have as large an impact on PM2.5 mass or bulk composition as they have on the number density of fine particles.
A systematic characterization of the atmospheric H2SO4-HNO3-NH3 system was conducted in the fog water, the aerosol, and the gas phase at a network of sites in the San Joaquin Valley of California. Spatial patterns of concentrations were established that reflect the distribution of SO2, NOx, and NH3 emissions within the valley. The concept of atmospheric alkalinity was introduced to interpret these concentrations in terms of the buffering capacity of the atmosphere with respect to inputs of strong acids. Regions of predominantly acidic and alkaline fog water were identified. Fog water was found to be alkaline in most of the valley, but small changes in emission budgets could lead to widespread acid fog. An extended stagnation episode was studied in detail: progressive accumulation of H2SO4-HNO3-NH3 species was documented over the course of the episode and interpreted in terms of production and removal mechanisms. Secondary production of strong acids H2SO4 and HNO3 under stagnant conditions resulted in a complete titration of available alkalinity at the sites farthest from NH3 sources. A steady SO2 conversion rate of 0.4-1.1% h-1 was estimated in the stagnant mixed layer under overcast conditions and was attributed to nonphotochemical heterogeneous processes. Removal of SO2 was enhanced in fog, compared to nonfoggy conditions. Conversion of NOx to HNO3 slowed down during the stagnation episode because of reduced photochemical activity; fog did not appear to enhance conversion of NOx. Decreases in total HNO3 concentrations were observed upon acidification of the atmosphere and were attributed to displacement of NO3- by H2SO4 in the aerosol, followed by rapid deposition of HNO3(g). The occurrence of fog was associated with general decreases of aerosol concentrations due to enhanced removal by deposition.
Measurements of pH variations within natural cloud drop populations reveal that small drops are often more acidic than large drops. Cloud samples collected from coastal stratus clouds, frontal clouds, and radiation fogs, from heavily polluted and pristine locations, had pH values ranging from below three to more than seven. Differences between small and large cloud drop acidities as large as two pH units were observed, although differences were generally below one pH unit. This chemical heterogeneity can significantly enhance oxidation of sulfur dioxide to sulfate within clouds, relative to oxidation rates predicted from the average cloudwater composition. One-third of the sampled clouds were estimated to experience an increase of at least 20% in the rate of sulfur oxidation by ozone (8% of the clouds had increases exceeding 100%) as a result of acidity differences between large and small cloud drops. These findings suggest that sulfate production within clouds, a critical component of the global sulfur cycle, may be more rapid than previously thought.
Measurements of particulate material and water vapor released in the
evaporation of cloud droplets are used to determine the amount and
concentration of material in the droplets. A counterflow virtual
impactor (CVI) is used to extract droplets from the surrounding air and
evaporate them in a flow of warm, dry, filtered air. Water vapor
concentrations, particle number, particulate light scattering, average
droplet and particle radii, and the aqueous-phase concentration of
nonvolatile, soluble, and insoluble material are determined. It is found
that the minimum radius of droplets varies within the interval 4-15
microns. Mesurements obtained in Sweden in 1986 near the base of
stratocumulus clouds show that solute concentrations increase with
droplet size by about a factor of 3 over the radius range 5-9 microns.
Tropospheric concentrations of formic and acetic acids in the gas, the aerosol, and the rainwater phases were determined in samples collected 1-2 m above ground level at an open field site in eastern Virginia. These acids were found to occur principally (98 percent or above) in the gas phase, with a marked annual seasonality, averaging 1890 ppt for formate and 1310 ppt for acetate during the growing season, as compared to 695 ppt and 700 ppt, respectively, over the nongrowing season. The data support the hypothesis that biogenic emissions from vegatation are important sources of atmospheric formic and acetic acid during the local growing season. The same time trends were observed for precipitation, although with less defined seasonality. The relative increase of the acetic acid/formic acid ratio during the nongrowing season points to the dominance of anthropogenic inputs of acetic acid from motor vehicles and biomass combustion in the wintertime.
HCOOH and CH3COOH are important chemical constituents of cloud water and
precipitation, but sources for these compounds in the atmosphere are at
present unknown. The question of source identification was addressed
through the analysis of 465 samples of precipitation collected at 14
continental and marine locations around the world. Continental
precipitation during growing seasons contained, relative to marine
precipitation and to continental precipitation during nongrowing
seasons, higher absolute concentrations of organic acids and higher
ratios of HCOO(T) to CH3COO(T). The concentrations of HCOO(T) and
CH3COO(T) in precipitation at most locations were also highly
correlated. These results support the hypothesis that organic acidity in
precipitation may originate with two major sources, volatile vegetative
constituents over continents and a second weaker source in both
continental and marine regions. Relative to the similar ratios of
HCOO(T) to CH3COO(T) in the aqueous phase, differences in precipitation
pH resulted in large regional differences in calculated equilibrium
vapor phase concentrations. The mechanism(s) by which proportionate
concentrations of HCOO(T) and CH3COO(T) are maintained in the aqueous
phase remains an open question. Comparisons between precipitation in
impacted and remote regions indicate that although possibly important
near large population and industrial centers, anthropogenic emissions
are probably not major sources for organic acids in precipitation over
broad geographic regions.
The importance of carbonyl compounds in Po Valley fog water chemistry is discussed. High concentrations of formaldehyde (HCHO) were detected in fog water (from 16 to 567 μM; average, 130 μM). The oxidant-limiting conditions during the fog season (fall-winter months) favour the presence of a large fraction of HCHO in the form of adducts with hydroxymethansulfonate: 85% of the total HCHO on average. Other carbonyl compounds were detected in the fog water: acetaldehyde, acrolein and acetone, but typically in much lower concentrations than formaldehyde. These other carbonyl compounds do not appear to be present in a bound form.
Dew and rainwater samples were collected during winter and monsoon periods in 1997–1998 at Rampur, India, a semiarid site with minimal anthropogenic activities. The study revealed that the decreasing order of ionic concentration in dew is Ca2+>SO42−>Cl−>Mg2+>NH4+>Na+>NO3−>K+>HCO−3>HCOO−>CH3COO−, while the range of pH was between 6.0 and 7.7 with a volume weighted mean pH value of 6.8. Rainwater pH varied from 5.9 and 7.4 with volume weighted mean pH of 6.6. The percentage contribution of alkaline components (Ca2+, Mg2+, Na+ and K+) was 43.9% and NH4+ 11.1%, while the contribution from acidic components was 45%. Similarly in rainwater the percentage contributions of alkaline, NH4+ and acidic components were 40.4%, 14.4% and 45.2%, respectively. The difference between the sum of cations and the sum of anions in dew was 233.8 μeq l−1, while in rainwater it was 27.8 μeq l−1 and their ratio was 1.2 in both dew and rainwater. A comparison of the ratios of Cl−/Ca2+, SO42−/Ca2+, Mg2+/Ca2+, Na+/Ca2+ and NO3−/Ca2+ in dew with soil indicated that 63 to 96 percentile samples in dew correspond to ratios in soil. Statistically significant correlation between Ca2+, Mg2+, K+, NO3−, SO42−, HCOO− and CH3COO− in dew indicate a significant contribution of NO3−, SO42−, HCOO− and CH3COO− from soil or they are associated with Ca2+, Mg2+ and K+ after neutralization. At the present site, in dew, NH4+ is 6 times, Ca2+ and Mg2+ more than 7 times, K+ and Na+ greater than 10 times and Cl−, NO3−, and SO42− are more than 9 times higher than those of rainwater. The steps governing dew composition are: (i) formation on dry deposition solids, (ii) dissolution of the soluble portion of the dry deposition by dew water, and (iii) sorption of gaseous NH3, formate and acetate into dew water.
The first observations of size-dependent cloud and fog drop inorganic ion and trace metal concentrations obtained using the Colorado State University 5-Stage cloud water collector (CSU 5-Stage) during field studies of orographic clouds (Whiteface Mountain, NY, July 1998) and radiation fogs (Davis, CA, January 1999) are reported. Although some mixing between drop sizes occurs, the CSU 5-Stage effectively separates the largest drops (>≈30μm in diameter) from the smallest ones (
Trace levels of PCDD and PCDF were detected in fog samples collected in Dübendorf, Switzerland. The more chlorinated, less toxic isomers predominated. Octachlorodibenzodioxin (OCDD) was the most abundant congener at 0.3-3 1 ng/L. No 2,3,7,8- TCDD or TCDF were detected. Congener class profiles were similar to those reported for air and rain samples, suggesting similar sources. Higher PCDD/PCDF levels in fog compared with reported levels in rain may be due to enhanced particle scavenging by fog.
Atmospheric gas- and particle-phase carboxylic acids and related compounds were measured during October 1991 in a semiurban site in northeastern United States. Formic and acetic acid were present in the atmosphere mostly in the gaseous form with less than 10% in the particle phase. Concentrations of formic acid and acetic acid were in the 0.80–2.5 and 0.60–3.4 ppbv ranges, respectively. Formic acid was correlated with acetic acid (r=0.94). Diurnal variations of formic acid were similar to those of ozone. This pattern is consistent with photochemical production as an important source. Formic-to-acetic acid ratios less than one were recorded, likely due to an increase in acetic acid contribution from direct emissions associated with vehicular traffic. Formaldehyde levels began to decrease after the mid-afternoon maxima; concentrations varied from 0.63 to 3.7 ppbv. Seven carboxylic acids (formic, acetic, pyruvic, glyoxalic, oxalic, succinic, and malonic) in the particle phase were identified. Aerosol carboxylic acid concentrations varied from 26 to 360 ng m−3. About 80% of the carboxylic acid aerosol mass was in the size fraction below 1.0 μm diameter. Of the dicarboxylic acids, oxalic acid was the most abundant species, followed by succinic acid and malonic acid. Particulate total organic carbon exhibited a concentration range of 12.6 × 103−49.9 × 103 ng Cm−3. The observed amounts of carboxylic acids in the particle phase accounted for a small fraction of the organic carbon. Results indicated that photochemical processes and anthropogenic emissions such as automobile exhaust are major sources of atmospheric carboxylic acids.
Humic-like substances have recently become candidates for making up an important fraction of bulk organic carbon in various atmospheric samples. Their properties were exploited by various analytical — mostly spectroscopic — techniques. For lack of any decisive analytical evidence, their presence in the samples was proved only by comparison with arbitrarily selected humic or fulvic acid standards. This series of evidences requires as many independent principles of determination as possible to minimise false identification and to better characterise the properties of the bulk organic matter, which may also be important in various atmospheric processes. In this paper, we used anodic stripping voltammetry to characterise the complexing and electrochemical behaviour of organic matter in fog water under conditions prevalent in most surface waters. Although the method provided no quantitative information, important interference effects — formation of electrochemically labile complexes, adsorption on the working electrode, complex dissociation, etc. — were observed. Evaluation of the results revealed all of the major electrochemical attributes of natural complexants as had been reported for humic or fulvic acids. These may provide indirect evidence that natural complexants similar to humic or fulvic acids are present in fog water in concentrations sufficiently large to produce these effects. This finding, which supplements previous independent measurements, may be useful in assessing the sources and effects of humic-like substances in atmospheric samples.
There is a growing interest in the potential formation of secondary organic aerosol (SOA) through reactions of organic compounds in condensed aqueous phases. In this study, the potential formation of SOA from aqueous-phase reactions of organic species was investigated. A new proposed aqueous-phase chemistry mechanism is coupled with the existing gas-phase Caltech Atmospheric Chemistry Mechanism (CACM) and the Model to Predict the Multiphase Partitioning of Organics (MPMPO). The proposed aqueous-phase chemistry mechanism treats organic reactions based on previous work by Ervens et al. (2004) and Lim et al. (2005) for organic species of carbon numbers up to four and the protocol proposed by Aumont et al. (2000) for organics of carbon numbers greater than four. Box model simulations were performed for tropospheric conditions with clouds present for a few hours in a day. The proposed aqueous-phase chemistry mechanism was also incorporated into the Community Multiscale Air Quality Model (CMAQ) with CACM/MPMPO and applied to a previously studied photochemical episode focusing on the eastern United States during the period of August 3-4, 2004. Preliminary three-dimensional air quality modeling study indicates that maximum contribution of SOA formation from aqueous-phase reactions of organics is approximately 0.28 mug/m3 for 24- hour average concentrations and 0.60 mug/m3 for one-hour average concentrations at certain locations. On average, domain-wide surface SOA predictions over the episode are increased by 8.6% when the aqueous- phase processing of organics is considered.
Limited information is available on the nature of organic compounds in
the tropospheric aerosol and their effect on aerosol hygroscopic
properties and cloud condensation nuclei (CCN) ability. Here we analyze
samples of liquid droplets and interstitial aerosol, concurrently
collected during fog episodes, to determine how the organic compounds
are partitioned between the two reservoirs. By comparing the nature and
concentration of different organic carbon classes found in the two
reservoirs, we find that fog acts as an efficient separator for carbon
(C) species on the basis of their chemical properties, with polar water
soluble species representing the greater part of total C within fog
droplets, and water insoluble C species preferentially found in the
interstitial reservoir. Water-soluble organic species are scavenged by
fog droplets to a comparable extent to major inorganic ions and are
therefore expected to play an important role in the droplet nucleation
process. The main classes of water soluble organic carbon (WSOC)
identified in fog water and interstitial aerosol by the techniques
traditionally used in aerosol analysis are aliphatic dicarboxylic acids,
sugars, aliphatic alcohols, and aliphatic carboxylic acids. However,
such species, ˜120 individual compounds, only account for a few
percent (<5% on average) of total WSOC. A new class of water soluble
macromolecular compounds (MMC), detected in aerosol samples from
different areas of the globe, are found to constitute a large fraction
(˜40% on average) of WSOC in the fog system (fog droplets plus
interstitial aerosol) and represent the main class of water soluble
species identified. More than 50% of WSOC still remains undetermined.
Water-soluble organic compounds (WSOC) often represent a large fraction of the total organic mass found in the atmospheric aerosol. They play a very important role in determining the ability of aerosol particles to act as cloud condensation nuclei (CCN), influencing cloud and fog formation and cloud albedo. Molecular characterization of WSOC in fogwater samples was achieved using a two-stage ion-trap mass spectrometer equipped with electrospray ionization (ESIMS/MS). Negative ionization conditions in the electrospray interface finalized our characterization of the acidic fraction of WSOC that comprises both mono- and di-carboxylic acids and polycarboxylic acids for which a similarity was suggested with naturally occurring humic (or fulvic) acids, and which are sometimes referred to in the literature as humic-like substances (HULIS). Molecular structure elucidation was accomplished using several model compounds and exploiting mass spectral resolution for compound separation. Single compound identification was attempted by recording typical MS/MS fragmentation pathways of model substances and comparing them with actual sample pathways in order to establish specific correspondences. Besides this spectrum-matching identification process, MS/MS interpretation led to several hypothetical structures for HULIS, extending the comprehension of their chemical nature. Suwannee River fulvic acid, proposed as a suitable model for representing the complex mixtures of HULIS in cloud and water aerosol extracts, was also analyzed, and the data obtained were compared with those from WSOC.
Polar organic matter (extracted from inhalable particles collected in Elizabeth, NJ, and from National Institute of Standards and Technology Standard Reference Material SRM 1649) has been characterized by determining elemental and ionic composition, chemical classes, and mutagenic activity. The acetone extracts of SRM 1649 and Elizabeth, NJ, samples were 46 and 40% carbon, respectively. When compared to the NJ extract, the SRM extract was enriched in aldehydes and ketones and deficient in carboxylic acids. Significant amounts of organic nitrogen were found in both extracts. Infrared spectra and class tests suggested the presence of nitro compounds, organic nitrates or nitrites, amines, and amides. Fluorescence suggested the presence of polycyclic aromatic species. For SRM 1649 the acetone extracts accounted for 36% (-S9) and 40% (+S9) of the mutagenic activity in the Ames assay with TA98 (specific mutagenic activity). The acetone extract of SRM 1649 had about four times greater mutagenic activity than that from the NJ particles. Both extracts showed substantial decreases in mutagenic activity when tested with nitroreductase-deficient strains of TA98. A simple resolubilization of the NJ extract concentrated the most mutagenic components into the least polar of the three fractions. 29 refs., 3 figs., 5 tabs.
IntroductionAtmospheric AerosolFormation of Individual Cloud Droplets and Ice Crystals in the AtmosphereFormation of Rain in Warm CloudsGrowth of Ice particles In Atmosphere
We have recently set up a new procedure for characterising the water soluble organic compounds (WSOC) in fog water, for which information is still rather limited. Fog samples collected during the 1998 – 1999 fall – winter season in the Po Valley (Italy) were analysed following this procedure, which allows a quantitative determination of three main classes of organic compounds (neutral species, mono-and di-carboxylic acids, polycarboxylic acids), together accounting for ca. 85% of the total WSOC. This procedure also provides information on the main chemical characteristics of these three classes of compounds (functional groups, aliphatic vs. aromatic character, etc.). The enhanced chemical knowledge on fog/cloud chemical composition opens new scenarios as far as chemical and microphysical processes in clouds and fogs are concerned. D 2002 Elsevier Science B.V. All rights reserved.
Concentration differences between small (r < 8.5="">m) and large droplets(r > 8.5 m) were observed for formic acid, acetic acid and formaldehyde in fog droplets collected in California''s Central Valley. The concentration ratios (large/small droplets) of these compounds were investigated by a stepwise model approach. Assuming thermodynamic equilibrium (KH
eff) results in an overestimate of the concentration ratios. Considering the time dependence of gas phase diffusion and interfacial mass transport, it appears that the lifetime of fog droplets might be sufficiently long to enable phase equilibrium for formaldehyde and acetic acid, but not for formic acid (at pH 7). Oxidation by the OH radical has no effect on formaldehyde concentrations but reduces formic acid concentrations uniformly in all drop size classes. The corresponding reaction for acetic acid is less efficient so that only in large droplets, where replenishment is slowed because the uptake rate of acid from the gas phase is slower, is the acid concentration reduced leading to a smaller concentration ratio. Formaldehyde concentrations in fog can be higher than predicted by Henry''s Law due to the formation of hydroxymethanesulfonate. Its formation is dependent on the sulfur(IV) concentration. At high pH values the uptake rate for sulfur(IV) is drop-size dependent. However, the observed concentration ratios for formaldehyde cannot be fully explained by the adduct formation. Finally, it is estimated that mixing effects, i.e., the combination of individual droplets into a bulk sample, have a minor influence (
Wet deposition due to radiation fog is examined in this paper. The area where the reported measurements were performed, the Po Valley, northern Italy, is characterized by both a high fog occurrence during the fall-winter months and fog water solutions of high ionic concentration and acidity.Estimated wet deposition for NH
4
+
, NO
inf3
sup-
and SO
inf4
sup2-
ions due to fog droplet settling to the ground accounts for 13.2, 12.1 and 5.3 percent with respect to bulk precipitations over the same period: January–March and October–December (fog season).Fog deposition rates show that this process can be an important pathway of trace gases and particles loss from the air. First indicative results of fog removal efficiency with respect to air particulate matter are presented.Dry deposition parameters should be taken into account in evaluating the potential effect of fog droplet deposition on vegetation.
In a standard reference air dust (NIST 1648 – urban particulate matter) as well as in airborne particulate matter collected in German urban and rural areas (Dortmund, Sauerland) 10% and more of the organic carbon can be attributed to macromolecular substances like humic and fulvic acids (HA, FA). Indirect evidence for the presence of humin was also obtained. HA and FA extracted from NIST 1648 and other urban and rural atmospheric particles using 0.1 m NaOH and isolated by ion-exchangers were characterized by their molecular-size distribution applying multistage ultrafiltration, their carbon content and their UV/VIS, Fourier-transformed infrared (FTIR) and nuclear magnetic resonance (1H-NMR) spectra. Summarizing, the structural studies exhibit that these humic-like substances (HULIS) contained in air dust samples are small in their molecular size and rich in aliphatic and carbohydrate substructures compared to HA and FA from soils and aquatic systems.
The aerosol at elevated sites in the South Coast Air Basin in California is a mixture of sea salt and pollution-derived secondary aerosol. The influence of sea salt declines with increasing distance from the coast. Nitric acid appears to react with the NaCl in sea salt aerosol to release HCl_(g) and form NaNO_3 in the aerosol. At inland sites, aerosol concentrations differ during periods of onshore and offshore flow. The highest concentrations were observed during the day when the onshore flow transported pollutants to the sites, while lower concentrations were observed at night when drainage flows from nearby mountains influenced the sites. Variations, in liquid water content are a major influence on cloudwater ion concentrations.
Comparisons of the ionic concentrations in two size-segregated fractions of cloudwater collected during several sampling intervals suggest that there is a large difference between the average composition of the smaller droplets and that of the larger droplets. The concentrations of Na^+, Ca^(2+) and Mg^(2+) in the large-droplet fraction were observed to be higher than in the small-droplet fraction, while the concentrations of SO_4^(2−), NO_3^−, NH_4^+ and H^+ were higher in the small-droplet fraction. Chloride concentrations were nearly equal in both fractions. Differences in the composition of size-fractionated cloudwater samples suggest that large droplets are formed on sea salt and soil dust, which are large aerosol, and small droplets are formed on small secondary aerosol composed primarily of (NH_4)_2SO_4 and NH_4NO_3. The concentrations of several components that exist partly in the gas phase (e.g. Cl^−, HCOOH and CH_3COOH) appear to be independent of droplet size.
Over the past decade, the chemical compositions of fogs and intercepted clouds have been investigated at more than a dozen locations across the United States. Sampling sites have been located in the northeast, southeast, Rocky Mountain, and west coast regions of the US. They include both pristine and heavily polluted locations. Frontal/orographic clouds (warm and supercooled), intercepted coastal stratiform clouds, and radiation fogs have all been examined. Sample pH values range from below 3 to above 7. Major ions also exhibit a wide concentration range, with clouds at some locations exhibiting high sea salt concentrations, while composition at other locations is dominated by ammonium and sulfate or nitrate.
Considerable effort has been put into characterizing the ionic composition of fogs and clouds over the past twenty-five years. Recently it has become evident that clouds and fogs often contain large concentrations of organic material as well. Here we report findings from a series of studies examining the organic composition of radiation fogs in central California. Organic compounds in these fogs comprise a major fraction of total solute mass, with total organic carbon sometimes reaching levels of several tens of mg/L. This organic matter is comprised of a wide variety of compounds, ranging from low molecular weight organic acids to high molecular weight compounds with molecular masses approaching several hundred to a thousand g/mole. The most abundant individual compounds are typically formic acid, acetic acid, and formaldehyde. High concentrations are also observed of some dicarboxylic acids (e.g., oxalate) and dicarbonyls (e.g., glyoxal and methylglyoxal) and of levoglucosan, an anhydrosugar characteristically emitted by biomass combustion. Many other compounds have been identified in fog water by GC/MS, including long chain n-alkanoic acids, n-alkanes, PAH, and others, although these compounds typically comprise a total of only a few percent of fog TOC. Measurements of fog scavenging of organic and elemental carbon reveal preferential scavenging of organic carbon. Tracking of individual organic compounds utilized as source type markers suggests the fogs differentially scavenge carbonaceous particles from different source types, with more active processing of wood smoke than vehicle exhaust. Observations of high deposition velocities of fog-borne organic carbon, in excess of 1 cm/s, indicate that fogs in the region represent an important mechanism for cleansing the atmosphere of pollution.
A detailed analysis of several versions of the Caltech Active Strand Cloudwater Collector (CASCC) is conducted. Efficiency calculations, design considerations and procedures for cloud liquid water content estimation from the collection rates of these instruments are discussed. The size-fractionating CASCC is capable of simultaneous collection of samples representing two portions of the cloud drop size spectrum. Large drops are collected in an inlet stage while smaller drops are collected in a second stage. Theoretical calculations, which assume no aerodynamic interaction between adjacent rows of collection rods in the inlet, suggest the inlet should have a 50% size cut corresponding to a drop size of 23 μm diameter. However, field test results suggest that focusing of the flow passing through a row of cylinders may increase the efficiency of collection on the subsequent cylinder row, thereby decreasing the overall size cut for the inlet. The CASCC2, a compact version of the original CASCC, is designed to sample the entire cloud drop spectrum. Comparison of the cloudwater collection rates of the CASCC2 and the size-fractionating CASCC showed good agreement when normalized by the flow rate through each collector. The Caltech Heated Rod Cloudwater Collector (CHRCC), designed for use in supercooled clouds, features a theoretical 50% lower size cut corresponding to a drop diameter of 9 μm. Liquid water content values estimated from the CHRCC cloudwater collection rates correlated reasonably well with values measured with a Gerber Particle Volume Monitor (PVM-100) in both warm (r2 = 0.83) and supercooled (r2 = 0.71) cloud conditions.
Hourly concentrations of ambient volatile organic compounds (VOCs) were analyzed between June and October 2003 at three sites, in order to further understand emissions of VOCs in the Houston area. Ambient concentrations of 54 VOCs from three monitoring sites in the heavily industrialized Houston Ship Channel were analyzed using positive matrix factorization (PMF). Hourly concentrations were divided into weekly data sets and analyzed to determine the most important source types that contribute to the measured VOC concentrations at these three sites. For each monitoring site, three or four sources were identified for each week as major contributors to ambient VOC concentrations using PMF. The sources isolated by the model are consistent with the chemical compositions of refinery, petrochemical and evaporative emissions, which are also the dominant inventoried sources of VOCs in Houston Ship Channel region. A night-time data analysis was also performed at two sites to investigate the effect of photochemical reactions on source attribution of VOCs.
During the spring, summer and fall seasons of 1990, we sampled fog at a coastal location in New England for chemical analysis. For the 6 sampled events, 72 h back trajectories were calculated for the associated air masses. We found that air masses leading to the sampled fog events reached our site from south/southwesterly to southeasterly directions. The chemical composition of the fog was temporally variable within a single event and even more so for event-to-event comparisons. The less polluted air masses originated over the Atlantic Ocean, but also showed influence of pollution which they may have picked up during their short travel time along the New England coast. The more polluted air masses traveled a significant amount of time over New England, some of them along the coast, and they probably became contaminated with regional pollution. This pattern explains the high concentrations of fog water compared to other sites in the U.S.A. as well as the high heterogeneity in our data set.
Drop size-resolved measurements of fog chemistry in California's San Joaquin Valley during the 1995 Integrated Monitoring Study reveal that fog composition varies with drop size. Small fog drops were less alkaline and typically contained higher major ion (nitrate, sulfate, ammonium) concentrations than large drops. Small drops often contained higher concentrations of Fe and Mn than large drops while H2O2 concentrations exhibited no strong drop size dependence. Simulation of an extended fog episode in Fresno, California revealed the capability of a drop size-resolved fog chemistry model to reproduce the measured (based on two drop size categories) drop size dependence of several key species. The model was also able to satisfactorily reproduce measured species-dependent deposition rates (ammonium>sulfate>nitrate) resulting from fog drop sedimentation. Both the model simulation and direct analysis of size-resolved fog composition observations and measured gas-phase oxidant concentrations indicate the importance of ozone as an aqueous-phase S(IV) oxidant in these high pH fogs. Due to the nonlinear dependence of the rate law for the ozone pathway on the hydrogen ion concentration, use of the average fog drop composition can lead to significant underprediction of aqueous phase sulfate production rates in these chemically heterogeneous fogs.
Fog was sampled at four locations in California’s San Joaquin Valley (SJV) during December 1995 and January 1996 as part of the 1995 Integrated Monitoring Study (IMS95). The fog sampling campaign was conducted in two phases. During the first phase, fog was sampled at three southern SJV surface locations, two urban (Fresno and Bakersfield) and one rural (near the Kern Wildlife Refuge). Both bulk samples (representative of the entire fog drop spectrum) and size-fractionated samples were collected. During the second phase, bulk fog samples were collected at three elevations on a 430 m television transmission tower in the northern SJV, representing some of the first observations of vertical variations in fog composition. SJV fog was observed to be consistently alkaline. The median pH measured in the southern SJV was 6.49, with a range from 4.97 to 7.43. Dominant species in the fog water were ammonium (median southern SJV concentration of 1008 microequivalents/l (μN)), nitrate (483 μN), sulfate (117 μN), acetate (117 μN), formate (63 μN), and formaldehyde (46 μM). Concentrations of the inorganic ions were similar in the urban and rural fogs, although occasionally much higher spikes of S(IV) and sulfate were observed in Bakersfield fog. Acetate, formaldehyde, and total organic carbon, by contrast, were observed to be present in greater concentration in the urban fogs. Bakersfield IMS95 fog concentrations of most species were similar to those measured there in the early 1980s, although concentrations of S(IV) and sulfate were much lower in IMS95 fogs. Significant differences were found between the composition of large and small fog drops, with pH differences at times exceeding one pH unit. The chemical heterogeneity present among SJV fog drop populations is likely to result in significant enhancement of aqueous sulfate production rates over those expected from average fog properties. Significant vertical variations were also observed in fog composition. Liquid water content was observed to increase strongly with elevation, while major ion aqueous concentrations in fog drops decreased with altitude. The total amount of solute contained within the fog (per unit volume of air) was observed to increase with altitude. These observations form a unique data set to be used for model evaluation and for further analysis of aerosol processing by fogs.
Six radiation fog episodes were sampled in the Central Valley of California during winter 1998/1999. Drop size-resolved fog samples were sampled using a size-fractionating Caltech active strand cloudwater collector (sf-CASCC). The sf-CASCC collects a large fog drop sample, comprised mainly of drops larger than 17 μm diameter, and a small fog drop sample, comprised mainly of drops with diameters between 4 and 17 μm. The fog pH was found to vary between approximately pH 5.3 and 6.8, with the pH of the large fog drop sample typically several tenths of a pH unit higher than the simultaneously collected small fog drop sample. At these high pH values, dissolved sulfur dioxide can be rapidly oxidized by a variety of chemical pathways and also can react quickly with dissolved formaldehyde to form hydroxymethanesulfonate. The amount of sulfate produced by aqueous-phase oxidation during each fog episode was determined by application of a tracer technique. The ratio of large : small drop S(IV) oxidation was compared with theoretically predicted ratios of large : small drop S(IV) oxidation rates. Although the higher pH of the large fog drops should promote more rapid S(IV) oxidation by ozone, finite rates of mass transport into the large drops and an increasing rate of complexation of S(IV) by formaldehyde at high pH combine to depress theoretically predicted rates of aqueous sulfate production in large fog drops below rates expected for small fog drops. This prediction is supported by the tracer results that indicate the concentration of sulfate resulting from aqueous-phase S(IV) oxidation in small drops generally exceeded the concentration formed in large drops. These findings stand in sharp contrast to observations in acidic clouds at Whiteface Mountain, New York, where hydrogen peroxide was determined to be the dominant S(IV) oxidant and the rate of S(IV) oxidation was found to be independent of drop size.
This work presents the chemical analysis of low weight carboxylic acids: formate and acetate in two droplet-size categories (2–6 and 5–8 μm) of fogwater collected in Strasbourg (eastern France) between 1991 and 1994. For each sample, the ratio between acetate and formate was calculated, in many cases, this ratio was typically higher than one. This calculation indicates that the origin of acetate and formate can be attributed to automobile exhaust. Maximum contribution of these acids to the total free acidity of fogwater was also checked and the results show that the contribution is very low in regard to the strong mineral acids from anthropogenic origin.
The carbon content of cloud water at a continental background site in Austria was studied during two intensive field campaigns in spring 1999 and 2000. Six carboxylic acids, total (TC) and black (BC) carbon as well as major inorganic ions were determined. Organic carbon (OC) was calculated as the difference between TC and BC. The most abundant carboxylic acids were acetic (average: 0.93 μg ml−1) and formic (0.61) followed by oxalic (0.38), succinic (0.15) and malonic (0.20) acids. Pyruvic acid was below the detection limit (<0.08) in all samples. The BC concentration was 1.15 and OC 4.81 μg ml−1 on average. Relating carboxylic acid concentrations to OC, the monocarboxylic acids alone represent 9.3% of OC. Adding the dicarboxylic acids, this average value increases to 11%. Although they are major components, no general trend could be seen between carboxylic acid and OC concentrations.
New stainless steel active fogwater collectors were designed and used in Davis (CA, USA) to collect fogwater for the speciation of organic matter. Organic compounds in fog samples were extracted by liquid–liquid extraction and analyzed by gas chromatography coupled to mass spectrometry. Numerous organic compounds, including various alkanes, polycyclic aromatic hydrocarbons (PAH) and alkanoic acids, have been identified in the fogwater samples. Higher molecular weight (MW) compounds are preferentially associated with an insoluble phase inside the fog drops, whereas lower molecular weight and more polar compounds are found predominantly in the dissolved phase. Concentrations in the dissolved phase were sometimes much higher than estimated by the compounds' aqueous solubilities.
In this paper the results of a systematic liquid chromatographic investigation are described to characterise water-soluble organic compounds in fog. A diode array detector is used to record the UV spectrum of the components during separation and a mass spectrometer is applied to obtain information on the ion masses of the constituents. The combination of UV and mass spectra reveal that the organic carbon content of fog water is distributed among a great number of acidic compounds which have polar functional groups and polyconjugated systems absorbing up to 500 nm. Due to the complexity of the organic fraction in fog water an unresolved hump of ions was recorded by the mass spectrometer from m/z=100–600 the most intense peaks being detected around m/z=200–250. Tannin and fulvic acid were also examined under the same conditions. In terms of complexity and ion distribution the mass spectrum of the organic fraction was similar to that of a fulvic acid reference material rather than to that of tannin.
Although organic nitrogen (ON) has been found to be a ubiquitous and significant component in wet and dry deposition, almost nothing is known about its concentration or composition in fog waters. To address this gap, we have investigated the concentration and composition of ON in fog waters collected in Davis, in California's Central Valley. Significant quantities of dissolved organic nitrogen (DON) were found in these samples, with a median concentration of 303 μM N (range=120–1630 μM N). DON typically represented approximately 16% of the total dissolved nitrogen (inorganic+organic) in Davis fog waters. The median concentration of nitrogen in free amino acids and alkyl amines was 16 μM N (range=3.8–120 μM N), which accounted for 3.4% of the DON in Davis fogs. Thus, although the absolute concentrations of free amino compounds were significant, they were only a minor component of the DON pool. Combined amino nitrogen (e.g., proteins and peptides) was present at higher concentrations and accounted for 6.1–29% (median=16%) of DON. Overall, free and combined amino compounds typically accounted for a median value of 22% of DON in the fog waters.
Oxalic acid is the most abundant dicarboxylic acid found in the troposphere, yet there is still no scientific consensus concerning its origins or formation process. Recent studies have suggested mechanisms for its formation in cloud water from gaseous precursors. Comparison of the characteristics of oxalic acid and nss sulfate, a chemical with a known in-cloud formation pathway, provides some support for an aqueous formation mechanism for oxalic acid. Analysis of the filters collected from the CIRPAS Twin Otter aircraft during CARMA I, a field campaign designed to study the marine stratocumulus off the coast of Monterey, CA, by a five stage Micro-Orifice Impactor (MOI) revealed a peak in the concentration distribution at a diameter of 0.26–0.44 μm, similar to the size distribution found for nss sulfate and corresponding to the droplet mode in the aerosol size distribution. An air-equivalent average of 2.03±0.47 μg m−3 (standard error) of sulfate was observed in the collected marine cloud water, in excess to below-cloud concentrations by 1.16 μg m−3 on average. This suggests in-cloud production similar in concentration to previous field campaigns in coastal marine atmospheres. Oxalate was observed in the clouds at air-equivalent concentrations of 0.21±0.04 μg m−3, in excess to below-cloud concentrations by 0.14 μg m−3 and suggesting an in-cloud production as well. The tentative identification in cloud water of one of the intermediate species in the aqueous oxalate production mechanism lends further support to an in-cloud oxalate source.
Twenty-four-hour precipitation samples from four sites: Dayalbagh (DB), Hari Parvat (HP), Taj Mahal (TM) and Udyog Kendra (UK) in Agra city, during the monsoon season (July–September) of 1991, were analysed for formate and acetate. Each site was representative of a different level of anthropogenic activity. The formate/acetate ratio observed appeared to be characteristic of the dominant activity at the site; the geometric means of the formate/acetate ratios calculated for individual samples were 0.99, 0.17, 0.83 and 0.21 for DB, HP, TM and UK, respectively. These corresponded to the level of pollution at the site. Direct acetate inputs from extensive combustion and automobile exhaust could contribute to elevated levels of the species at two of the four sites. Another possible indirect input could be from the alkaline hydrolysis of PAN, aided by relatively high pH values of rain water (volume-weighted averages = 6.79, 6.69, 7.22, 7.15) at the four sites.