Article

Observations of fine and coarse particle nitrate at several rural locations in the United States

April 2008
Atmospheric Environment 42(11):2720-2732

April 2008
42(11):2720-2732

DOI:10.1016/j.atmosenv.2007.05.016

Authors:

Taehyoung Lee

Hankuk University of Foreign Studies

Xiao-Ying Yu

Oak Ridge National Laboratory

Sonia M Kreidenweis

Colorado State University

Show all 6 authorsHide

Nitrate comprises an important part of aerosol mass at many non-urban locations during some times of the year. Little is known, however, about the chemical form and size distribution of particulate nitrate in these environments. While submicron ammonium nitrate is often assumed to be the dominant species, this assumption is rarely tested. Properties of aerosol nitrate were characterized at several IMPROVE monitoring sites during a series of field studies. Study sites included Bondville, Illinois (February 2003), San Gorgonio Wilderness Area, California (April and July 2003), Grand Canyon National Park, Arizona (May 2003), Brigantine National Wildlife Refuge, New Jersey (November 2003), and Great Smoky Mountains National Park, Tennessee (July/August 2004). Nitrate was found predominantly in submicron ammonium nitrate particles during the Bondville and San Gorgonio (April) campaigns. Coarse mode nitrate particles, resulting from reactions of nitric acid or its precursors with sea salt or soil dust, were more important at Grand Canyon and Great Smoky Mountains. Both fine and coarse mode nitrate were important during the studies at Brigantine and San Gorgonio (July). These results, which complement earlier findings about the importance of coarse particle nitrate at Yosemite and Big Bend National Parks, suggest a need to more closely examine common assumptions regarding the importance of ammonium nitrate at non-urban sites, to include pathways for coarse mode nitrate formation in regional models, and to consider impacts of coarse particle nitrate on visibility. Because coarse particle nitrate modes often extend well below 2.5 μm aerodynamic diameter, measurements of PM2.5 nitrate in these environments should not automatically be assumed to contain only ammonium nitrate.

PM2.5 in Carlsbad Caverns National Park: Composition, sources, and visibility impacts

Article

May 2022

Carlsbad Caverns National Park in southeastern New Mexico is adjacent to the Permian Basin, one of the most productive oil and gas regions in the country. The 2019 Carlsbad Caverns Air Quality Study (CarCavAQS) was designed to examine the influence of regional sources, including urban emissions, oil and gas development, wildfires, and soil dust on air quality in the park. Field measurements of aerosols, trace gases, and deposition were conducted from 25 July through 5 September 2019. Here we focus on observations of fine particles and key trace gas precursors to understand important contributing species and their sources and associated impacts on haze. Key gases measured included aerosol precursors: nitric acid and ammonia, and oil and gas tracer: methane. High-time resolution (6-minute) PM2.5 mass ranged up to 31.8 µg m-3, with an average of 7.67 µg m-3. The main inorganic ion contributors were sulfate (avg 1.3 µg m-3), ammonium (0.30 µg m-3), calcium (Ca2+) (0.22 µg m-3), nitrate (0.16 µg m-3), and sodium (0.057 µg m-3). The WSOC concentration averaged 1.2 µg C m-3. Sharp spikes were observed in Ca2+, consistent with local dust generation and transport. Ion balance analysis and abundant nitric acid suggest PM2.5 nitrate often reflected reaction between nitric acid and sea salt, forming sodium nitrate, and between nitric acid and soil dust containing calcium carbonate, forming calcium nitrate. Sulfate and soil dust are the major contributors to modeled light extinction in the 24-hour average daily IMPROVE observations. Higher time resolution data revealed a maximum 1-hour extinction value of 90 Mm-1 (excluding coarse aerosol) and included periods of significant light extinction from BC as well as sulfate and soil dust. Residence time analysis indicated enrichment of sulfate, BC, and methane during periods of transport from the southeast, the direction of greatest abundance of oil and gas development.

Evaluation of the Community Multiscale Air Quality (CMAQ) model v5.0 against size-resolved measurements of inorganic particle composition across sites in North America

Article

Full-text available

Sep 2015

This work evaluates particle size–composition distributions simulated by the Community Multiscale Air Quality (CMAQ) model using micro-orifice uniform deposit impactor (MOUDI) measurements at 18 sites across North America. Size-resolved measurements of particulate SO42−, NO3−, NH4+, Na+, Cl−, Mg2+, Ca2+, and K+ are compared to CMAQ model output for discrete sampling periods between 2002 and 2005. The observation sites were predominantly in remote areas (e.g., National Parks) in the USA and Canada, and measurements were typically made for a period of roughly 1 month. For SO42− and NH4+, model performance was consistent across the USA and Canadian sites, with the model slightly overestimating the peak particle diameter and underestimating the peak particle concentration compared to the observations. Na+ and Mg2+ size distributions were generally well represented at coastal sites, indicating reasonable simulation of emissions from sea spray. CMAQ is able to simulate the displacement of Cl− in aged sea spray aerosol, though the extent of Cl− depletion relative to Na+ is often underpredicted. The model performance for NO3− exhibited much more site-to-site variability than that of SO42− and NH4+, with the model ranging from an underestimation to overestimation of both the peak diameter and peak particle concentration across the sites. Computing PM2.5 from the modeled size distribution parameters rather than by summing the masses in the Aitken and accumulation modes resulted in differences in daily averages of up to 1 μg m−3 (10 %), while the difference in seasonal and annual model performance compared to observations from the Interagency Monitoring of Protected Visual Environments (IMPROVE), Chemical Speciation Network (CSN), and Air Quality System (AQS) networks was very small. Two updates to the CMAQ aerosol model – changes to the assumed size and mode width of emitted particles and the implementation of gravitational settling – resulted in small improvements in modeled size distributions.

Characterization of PM10 over urban and rural sites of Rajnandgaon, central India

Article

Full-text available

Jan 2016
NAT HAZARDS

Balram Ambade

The main aim of this study is to determine the water-soluble species of PM10 (particles having an aerodynamic diameter less than 10 μm) in urban and rural sites of Rajnandgaon district, central India, in 2009. The samples were collected on quartz fiber filters and analyzed for the major water-soluble ions Cl−, (Formula presented.), (Formula presented.), (Formula presented.), Na+, K+, Mg2+ and Ca2+ parameters, employing ion chromatograph. These species show large spatial and temporal variations. On urban site, the ambient PM10 concentration has been observed to be the highest 167 ± 64 μg m−3 (winter) followed by 141 ± 65 μg m−3 (post-monsoon), 112 ± 53 μg m−3 (pre-monsoon) and lowest 34 ± 13 μg m−3 (high monsoon), whereas in rural background, the PM10 concentration was highest 153 ± 54 μg m−3 (winter) followed by 122 ± 53 μg m−3 (post-monsoon), 102 ± 39 μg m−3 (pre-monsoon) and lowest 32 ± 11 μg m−3 (high monsoon). The measured concentrations were excess of annual averages specified by the Indian National Ambient Air Quality Standards of PM10 60 μg m−3. Simultaneously, the measurement of organic carbon (OC) and elemental carbon (EC) was also taken. The annual concentration of OC and EC in urban site was found to be 5.9 and 4.8 μg m−3, but in the rural site, the concentration was 3.11 and 2.78 μg m−3 with OC/EC ratios 1.90 and 1.73 in urban and rural sites, respectively. Higher levels were obtained at urban site as compared to rural site. This suggested that the urban site exhibited a more serious climatic impact on the background air.

Summertime PM2.5 ionic species in four major cities of China: nitrate formation in an ammonia-deficient atmosphere

Article

Full-text available

Jun 2008

Strong atmospheric photochemistry in summer can produce a significant amount of secondary aerosols, which may have a large impact on regional air quality and visibility. In the study reported herein, we analyzed sulfate, nitrate, and ammonium in PM2.5 samples collected using a 24-h filter system at suburban and rural sites near four major cities in China (Beijing, Shanghai, Guangzhou, and Lanzhou). Overall, the PM2.5 mass concentrations were high (with a mean value of 55–68 gμgm−3), which reflects the long-known particulate pollution in China's large urban centers. We observed very high concentrations of sulfate and nitrate at the Beijing and Shanghai sites, and, in particular, abnormally high levels of nitrate (24-h average concentration up to 42 gμgm−3 and contributing up to 25% of the PM2.5 mass) in the ammonium-poor samples. The Beijing and Shanghai aerosols were characterized by high levels of aerosol acidity (~220–390 nmol m−3) and low levels of in-situ pH (−0.77 to −0.52). In these samples, the formation of the observed high concentrations of particulate nitrate cannot be explained by homogeneous gas-phase reaction between ammonia and nitric acid. Examination of the relation of nitrate to relative humidity and aerosol loading suggests that the nitrate was most probably formed via the heterogeneous hydrolysis of N2O5 on the surface of the moist and acidic aerosols in Beijing and Shanghai. In comparison, the samples collected in Lanzhou and Guangzhou were ammonium-rich with low levels of aerosol acidity (~65–70 nmol m−3), and the formation of ammonium nitrate via the homogeneous gas-phase reaction was favored, which is similar to many previous studies. An empirical fit has been derived to relate fine nitrate to aerosol acidity, aerosol water content, aerosol surface area, and the precursor of nitrate for the data from Beijing and Shanghai.

Influence of crustal dust and sea spray supermicron particle concentrations and acidity on inorganic NO3− Aerosol during the 2013 Southern Oxidant and Aerosol Study

Article

Full-text available

May 2015
ACP

The inorganic aerosol composition was measured in the southeastern United States, a region that exhibits high aerosol mass loading during the summer, as part of the 1 June to 15 July 2013 Southern Oxidant and Aerosol Study (SOAS) campaign. Measurements using a Monitor for AeRosols and GAses (MARGA), an ion chromatograph coupled with a wet rotating denuder and a steam-jet aerosol collector for monitoring of ambient inorganic gas and aerosol species, revealed two periods of high aerosol nitrate (NO3−) concentrations during the campaign. These periods of high nitrate were correlated with increased concentrations of coarse mode mineral or sea spray aerosol species, particularly Na+ and Ca2+, and with a shift towards aerosol with larger (1 to 2.5 μm) diameters. We suggest this nitrate aerosol forms by multiphase reactions of HNO3 and particles, reactions that are facilitated by transport of mineral dust and sea spray aerosol from a source within the United States. The observed high aerosol acidity prevents the formation of NH4NO3, the inorganic nitrogen species often dominant in fine-mode aerosol at higher pH. Calculation of the rate of the heterogeneous uptake of HNO3 on mineral aerosol supports the conclusion that aerosol NO3− is produced primarily by this process, and is likely limited by the availability of mineral dust surface area. Modeling of NO3− and HNO3 by thermodynamic equilibrium models (ISORROPIA II and E-AIM) reveals the importance of including mineral cations in the southeastern United States to accurately balance ion species and predict gas/aerosol phase partitioning.

Evaluation of the Community Multiscale Air Quality (CMAQ) model v5.0 against size-resolved measurements of inorganic particle composition across sites in North America

Article

Full-text available

May 2015
GMDD

This work evaluates particle size-composition distributions simulated by the Community Multiscale Air Quality (CMAQ) model using Micro-Orifice Uniform Deposit Impactor (MOUDI) measurements at 18 sites across North America. Size-resolved measurements of particulate SO42−, NO3−, NH4+, Na+, Cl−, Mg2+, Ca2+ and K+ are compared to CMAQ model output for discrete sampling periods between 2002 and 2005. The observation sites were predominantly in remote areas (e.g. National Parks) in the United States and Canada, and measurements were typically made for a period of roughly one month. For SO42− and NH4+, model performance was consistent across the US and Canadian sites, with the model slightly overestimating the peak particle diameter and underestimating the peak particle concentration compared to the observations. Na+ and Mg2+ size distributions were generally well represented at coastal sites, indicating reasonable simulation of emissions from sea spray. CMAQ is able to simulate the displacement of Cl− in aged sea spray aerosol, though the extent of Cl− depletion relative to Na+ is often underpredicted. The model performance for NO3− exhibited much more site-to-site variability than that of SO42− and NH4+, with the model ranging from an underestimation to overestimation of both the peak diameter and peak particle concentration across the sites. Computing PM2.5 from the modeled size distribution parameters rather than by summing the masses in the Aitken and accumulation modes resulted in differences in daily averages of up to 1 μg m−3 (10%), while the difference in seasonal and annual model performance compared to observations from the IMPROVE, CSN and AQS networks was very small. Two updates to the CMAQ aerosol model – changes to the assumed size and mode width of emitted particles and the implementation of gravitational settling – resulted in small improvements in modeled size distributions.

Homogeneous and heterogeneous photolysis of nitrate in the atmosphere: state of the science, current research needs, and future prospects

Article

Full-text available

Nov 2022

Nitrate is an important component of atmospheric particulate matter and affects air quality, climate, human health, and the ecosystem. Nitrate was previously considered a permanent sink for nitrogen oxides (NO x ). However, this viewpoint has been challenged in recent years because growing research evidence has shown the transformation of nitrate into NO x (i.e., renoxification). The photolysis of nitrate/HNO 3 , especially in the particulate phase or adsorbed on particles, can be a significant renoxification process in the atmosphere. The formation and photolysis of nitrate in aerosol not only change the diurnal variation of NO x , but also provide long-distance transport of NO x in the form of nitrate, which affects local and regional atmospheric chemistry and air quality. This review summarizes recent advances in the fundamental understanding of the photolysis of nitrate/HNO 3 under various atmospheric conditions, with a focus on mechanisms and key factors affecting the process. The atmospheric implications are discussed and future research is recommended.

The Acidity of Atmospheric Particles and Clouds

Preprint

Full-text available

Oct 2019

Abstract. Acidity, defined as pH, is a central component of aqueous chemistry. In the atmosphere, the acidity of condensed phases (aerosol particles, cloud water, and fog droplets) governs the phase partitioning of semi-volatile gases such as HNO3, NH3, and HCl, as well as chemical reaction rates. It has implications for the atmospheric lifetime of pollutants, deposition, and human health. Despite its fundamental role in atmospheric processes, only recently has this field seen a growth in the number of studies on particle acidity. Even with this growth, many fine particle pH estimates must be based on thermodynamic model calculations since no operational techniques exist for direct measurements. Current information indicates acidic fine particles are ubiquitous, but observationally-constrained pH estimates are limited in spatial and temporal coverage. Clouds and fogs are also generally acidic, but to a lesser degree than particles, and have a range of pH that is quite sensitive to anthropogenic emissions of sulfur and nitrogen oxides, as well as ambient ammonia. Historical measurements indicate that cloud and fog droplet pH has changed in recent decades in response to controls on anthropogenic emissions, while the limited trend data for aerosol particles indicates acidity may be relatively constant due to the semi-volatile nature of the key acids and bases and buffering in particles. This paper reviews and synthesizes the current state of knowledge on the acidity of atmospheric condensed phases, specifically particles and cloud droplets. It includes recommendations for estimating acidity and pH, standard nomenclature, a synthesis of current pH estimates based on observations, and new model calculations on the local and global scale.

Urban and rural coarse aerosol mass across the United States: Spatial and seasonal variability and long-term trends

Article

Oct 2019

Coarse aerosol mass (CM = PM10 − PM2.5, mass of particles with aerodynamic diameters between 2.5 and 10 μm) has important environmental and climate impacts. Examining the spatial and temporal variability of CM is important for understanding its sources and transport, evaluating its environmental impacts, and designing mitigation strategies. CM was computed at 195 collocated U.S. Environmental Protection Agency (EPA) PM10 and PM2.5 Federal Reference Method (FRM) sites from 2000 through 2016. These data were integrated with remote/rural CM data at 155 sites from the IMPROVE (Interagency Monitoring of Protected Visual Environments) network to create a continental-scale dataset of daily, monthly, seasonal, and annual mean CM concentrations, as well as regionally aggregated data. Annual mean average continental United States (CONUS) urban CM concentrations were twice that of rural CM concentrations (10.5 μg m−3 versus 4.9 μg m−3, respectively) for 2012–2016. The highest CM concentrations occurred in the Southwest in spring, the central United States in summer and fall, and southern California nearly year-round. The lowest CM concentrations occurred in the Intermountain West, northwestern United States, and regions in the East. While urban CM concentrations were higher, CONUS average urban and rural CM/PM10 fractions were similar, with an annual mean fraction of 0.5. However, many regions, especially across the West, experienced much higher fractions (>0.7) depending on season. Regional mean CM weekly cycles with lower weekend concentrations were observed at both urban and rural sites throughout most of the country, indicating anthropogenic influence. Trend analyses suggest spring and summer mean CM has increased significantly at some remote and urban sites over the 2000–2016 period, especially at sites in the central and eastern United States. However, CONUS annual mean urban CM has decreased significantly (p < 0.05) at a rate of −1.8% yr−1 compared to an insignificant increase of 0.5% yr−1 at rural sites. Urban and rural relative contributions of CM to PM10 have increased since 2000 due to the strong reductions of PM2.5 mass. Understanding CM seasonal and temporal variability, composition, and sources is increasingly important in order to develop effective mitigation strategies for managing its environmental and climate impacts.

Spatial and seasonal variability in fine mineral dust and coarse aerosol mass at remote sites across the United States: Fine mineral dust and coarse mass

Article

Mar 2017

Understanding the spatial and temporal variability in fine mineral dust (FD, mineral aerosols with diameters less than 2.5 μm) and coarse aerosol mass (CM, mass of aerosols with diameters between 2.5 and 10 μm) is important for accurately characterizing and perhaps mitigating their environmental and climate impacts. The spatial and seasonal variability of ambient FD and CM was characterized at rural and remote sites across the United States for 2011–2014 using concentration and elemental chemistry data from the Interagency Monitoring of Protected Visual Environments (IMPROVE) aerosol monitoring network. FD concentrations were highest (and had ≥50% contributions to PM2.5 mass) in the southwestern United States in spring and across the central and southeastern United States in summer (20–30% of PM2.5 mass). CM was highest across the Southwest and southern Great Plains in spring and central United States in spring, summer, and fall (≥70% contributions to PM10 mass). Similar FD and CM seasonal variability was observed near source regions in the Southwest, but a seasonal decoupling was observed in most other regions, suggesting the contribution of non-local sources of FD or perhaps non-dust-related CM. The seasonal and spatial variability in FD elemental ratios (calcium, iron, and aluminum) was fairly uniform across the West; however, in the eastern United States a shift in summer elemental composition indicated contributions from non-local source regions (e.g., North Africa). Finally, long-term trend analyses (2000–2014) indicated increased FD concentrations during spring at sites across the Southwest and during summer and fall in the southeastern and central United States.

Mass Spectrometry Imaging Strategy for In Situ Quantification of Soot in Size-Segregated Air Samples

Article

Oct 2022
ANAL CHEM

Soot, mainly derived from incomplete combustion of fossil fuel and biomass, exists ubiquitously in different environmental matrixes. To study the detrimental effects of soot on climate, air quality, and human health, accurate quantification of soot is an important prerequisite. However, until now, quantification of soot in environmental media, especially in carbonaceous media, is still very challenging. Here, we report a matrix-free laser desorption/ionization mass spectrometry (LDI-MS) method for in situ imaging of soot particles in size-segregated aerosol samples collected on filter membranes. A series of round-shaped sample spots in filter membranes were selected and subjected to MS imaging analysis, enabling direct in situ quantification of soot without solvent extraction or separation. Especially, the MS imaging with serial sample spots can overcome the problems of sweet-spot in LDI-MS and inhomogeneous distribution of soot in the filter membrane, thus greatly improving the precision of quantification. The limit of detection of soot was 4 ng/m2 and the recovery was 84.4-126%. By using this method, we found that a higher soot content was present in larger-sized particulate matter than smaller-sized particles, suggesting that aerosol soot was mainly derived from primary emission sources. Furthermore, this method also shows the potential to analyze nitrate and sulfate species in PM2.5. To the best of our knowledge, it is the first method capable of simultaneous analysis of inorganic salts and soot in air samples. It represents a novel strategy for in situ quantification of aerosol soot with the advantages of high specificity, high sensitivity, separation-, solvent- and matrix-free.

Forest-atmosphere exchange of reactive nitrogen in a remote region -Part I: Measuring temporal dynamics

Article

Full-text available

Jan 2022
BG

Long-term dry deposition flux measurements of reactive nitrogen based on the eddy covariance or the aerodynamic gradient method are scarce. Due to the large diversity of reactive nitrogen compounds and high technical requirements for the measuring devices, simultaneous measurements of individual reactive nitrogen compounds are not affordable. Hence, we examined the exchange patterns of total reactive nitrogen (ΣNr) and determined annual dry deposition budgets based on measured data at a mixed forest exposed to low air pollution levels located in the Bavarian Forest National Park (NPBW), Germany. Flux measurements of ΣNr were carried out with the Total Reactive Atmospheric Nitrogen Converter (TRANC) coupled to a chemiluminescence detector (CLD) for 2.5 years. The average ΣNr concentration was 3.1 µg N m−3. Denuder measurements with DELTA samplers and chemiluminescence measurements of nitrogen oxides (NOx) have shown that NOx has the highest contribution to ΣNr (∼51.4 %), followed by ammonia (NH3) (∼20.0 %), ammonium (NH4+) (∼15.3 %), nitrate NO3- (∼7.0 %), and nitric acid (HNO3) (∼6.3 %). Only slight seasonal changes were found in the ΣNr concentration level, whereas a seasonal pattern was observed for the contribution of NH3 and NOx. NH3 showed highest contributions to ΣNr in spring and summer, NOx in autumn and winter. We observed deposition fluxes at the measurement site with median fluxes ranging from −15 to −5 ngNm-2s-1 (negative fluxes indicate deposition). Median deposition velocities ranged from 0.2 to 0.5 cm s−1. In general, highest deposition velocities were recorded during high solar radiation, in particular from May to September. Our results suggest that seasonal changes in composition of ΣNr, global radiation (Rg), and other drivers correlated with Rg were most likely influencing the deposition velocity (vd). We found that from May to September higher temperatures, lower relative humidity, and dry leaf surfaces increase vd of ΣNr. At the measurement site, ΣNr concentration did not emerge as a driver for the ΣNrvd. No significant influence of temperature, humidity, friction velocity, or wind speed on ΣNr fluxes when using the mean-diurnal-variation (MDV) approach for filling gaps of up to 5 days was found. Remaining gaps were replaced by a monthly average of the specific half-hourly value. From June 2016 to May 2017 and June 2017 to May 2018, we estimated dry deposition sums of 3.8 and 4.0 kgNha-1a-1, respectively. Adding results from the wet deposition measurements, we determined 12.2 and 10.9 kgNha-1a-1 as total nitrogen deposition in the 2 years of observation. This work encompasses (one of) the first long-term flux measurements of ΣNr using novel measurements techniques for estimating annual nitrogen dry deposition to a remote forest ecosystem.

Evaluation of interactive and prescribed agricultural ammonia emissions for simulating atmospheric composition in CAM-Chem

Preprint

Full-text available

Aug 2021

Ammonia (NH3) plays a central role in the chemistry of inorganic secondary aerosols in the atmosphere. The largest emission sector for NH3 is agriculture, where NH3 is volatilized from livestock wastes and fertilized soils. Although the NH3 volatilization from soils is driven by the soil temperature and moisture, many atmospheric chemistry models prescribe the emission using yearly emission inventories and climatological seasonal variations. Here we evaluate an alternative approach where the NH3 emissions from agriculture are simulated interactively using the process model FANv2 (Flow of Agricultural Nitrogen, version 2) coupled to the Community Atmospheric Model with Chemistry (CAM-chem). We run a set of six-year global simulations using the NH3 emission from FANv2 and three global emission inventories (EDGAR, CEDS and HTAP) and evaluate the model performance using a global set of multi-component (atmospheric NH3 and NH4+, and NH4+ wet deposition) in-situ observations. Over East Asia, Europe, and North America, the simulations with different emissions perform similarly when compared with the observed geographical patterns. The seasonal distributions of NH3 emissions differ between the inventories, and the comparison to observations suggests that both FANv2 and the inventories would benefit from more realistic timing of fertilizer applications. The largest differences between the simulations occur over data-scarce regions. In Africa, the emissions simulated by FANv2 are 200–300 % higher than in the inventories, and the available in-situ observations from Western and Central Africa, as well as NH3 retrievals from the IASI instrument, are consistent with the higher NH3 emissions as simulated by FANv2. Overall, in simulating ammonia and ammonium concentrations over regions with detailed regional emission inventories, the inventories based on these details (HTAP, CEDS) capture the atmospheric concentrations and their seasonal variability the best. However these inventories can not capture the impact of meteorological variability on the emissions, nor can these inventories couple the emissions to the biogeochemical cycles and their changes with climate drivers. Finally, we show with sensitivity experiments that the simulated time-averaged nitrate concentration in air is sensitive to the temporal resolution of the NH3 emissions. Over the CASTNET monitoring network covering the U.S., resolving the NH3 emissions hourly instead monthly reduced the positive model bias from approximately 80 % to 60 % of the observed yearly mean nitrate concentration. This suggests that some of the commonly reported overestimation of aerosol nitrate over the U.S. may be related to unresolved temporal variability in the NH3 emissions.

Stable 15 N isotopes in fine and coarse urban particulate matter

Article

Full-text available

Mar 2021

Particulate nitrogen has far-reaching negative effects on human health and the environment, and effective strategies for reducing it require understanding its sources and formation processes. To learn about these factors, we recorded size-resolved nitrogen isotope ratios (δ¹⁵N) of total particulate N at an urban site in northwest Germany during a four-week measuring campaign. We observed a steady decrease in δ¹⁵N when going from fine to coarse particles, with values between +18 ‰ and -2 ‰. This difference based on particle size is caused by different isotope fractionation processes during particle formation: The fine particles contain ammonium nitrate, which is formed in an equilibrium process, leading to an enrichment of ¹⁵N. Moreover, fine particles are more reactive due to their larger surface areas and relatively long residence times in the atmosphere, which leads to an additional enrichment of ¹⁵N; a key step of this process likely occurs when the ammonium particles interact with ammonia from agricultural sources. In contrast to fine particles, coarse particles are formed by direct absorption of HNO3 on pre-existing particles; the HNO3 stems from traffic emissions of NOx and subsequent oxidation in the atmospheric gas phase. Because only a small amount of isotope fractionation is associated with non-equilibrium processes during phase transitions, there is less ¹⁵N enrichment in the coarse particles. Overall, nitrogen isotopes clearly reflect the different formation processes of fine and coarse aerosol particles.

Fine and Coarse Carbonaceous Aerosol in Houston, TX, during DISCOVER-AQ

Article

Full-text available

May 2020

To investigate major sources and trends of particulate pollution in Houston, total suspended particulate (TSP) and fine particulate matter (PM2.5) samples were collected and analyzed. Characterization of organic (OC) and elemental (EC) carbon combined with realtime black carbon (BC) concentration provided insight into the temporal trends of PM2.5 and coarse PM (subtraction of PM2.5 from TSP) during the Deriving Information on Surface Conditions from Column and VERtically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) Campaign in Houston in 2013. Ambient OC, EC, and BC concentrations were highest in the morning, likely due to motor vehicle exhaust emissions associated with the morning rush hour. The morning periods also had the lowest OC to EC ratios, indicative of primary combustion sources. Houston also had significant coarse EC at the downtown site, with an average (±standard deviation) PM2.5 to TSP ratio of 0.52 ± 0.18 and an average coarse EC concentration of 0.44 ± 0.24 µg·C·m−3. The coarse EC concentrations were likely associated with less efficient industrial combustion processes from industry near downtown Houston. During the last week (20–28 September, 2013), increases in OC and EC concentrations were predominantly in the fine fraction. Both PM2.5 and TSP samples from the last week were further analyzed using radiocarbon analysis. Houston’s carbonaceous aerosol was determined to be largely from contemporary sources for both size fractions; however, PM2.5 had less impact from fossil sources. There was an increasing trend in fossil carbon during a period with the highest carbonaceous aerosol concentrations (September 24 night and 25 day) that was observed in both the PM2.5 and TSP. Overall, this study provided insight into the sources and trends of both fine and coarse PM in a large urban U.S. city impacted by a combination of urban, industrial, and biogenic emissions sources.

The Acidity of Atmospheric Particles and Clouds

Article

Full-text available

Apr 2020
ATMOS CHEM PHYS

Acidity, defined as pH, is a central component of aqueous chemistry. In the atmosphere, the acidity of condensed phases (aerosol particles, cloud water, and fog droplets) governs the phase partitioning of semivolatile gases such as HNO3, NH3, HCl, and organic acids and bases as well as chemical reaction rates. It has implications for the atmospheric lifetime of pollutants, deposition, and human health. Despite its fundamental role in atmospheric processes, only recently has this field seen a growth in the number of studies on particle acidity. Even with this growth, many fine-particle pH estimates must be based on thermodynamic model calculations since no operational techniques exist for direct measurements. Current information indicates acidic fine particles are ubiquitous, but observationally constrained pH estimates are limited in spatial and temporal coverage. Clouds and fogs are also generally acidic, but to a lesser degree than particles, and have a range of pH that is quite sensitive to anthropogenic emissions of sulfur and nitrogen oxides, as well as ambient ammonia. Historical measurements indicate that cloud and fog droplet pH has changed in recent decades in response to controls on anthropogenic emissions, while the limited trend data for aerosol particles indicate acidity may be relatively constant due to the semivolatile nature of the key acids and bases and buffering in particles. This paper reviews and synthesizes the current state of knowledge on the acidity of atmospheric condensed phases, specifically particles and cloud droplets. It includes recommendations for estimating acidity and pH, standard nomenclature, a synthesis of current pH estimates based on observations, and new model calculations on the local and global scale.

Effects of NH3 and alkaline metals on the formation of particulate sulfate and nitrate in wintertime Beijing

Article

Feb 2020
SCI TOTAL ENVIRON

Sulfate and nitrate from secondary reactions remain as the most abundant inorganic species in atmospheric particle matter (PM). Their formation is initiated by oxidation (either in gas phase or particle phase), followed by neutralization reaction primarily by NH3, or by other alkaline species such as alkaline metal ions if available. The different roles of NH3 and metal ions in neutralizing H2SO4 or HNO3, however, are seldom investigated. Here we conducted semi-continuous measurements of SO42-, NO3-, NH4+, and their gaseous precursors, as well as alkaline metal ions (Na+, K+, Ca2+, and Mg2+) in wintertime Beijing. Analysis of aerosol acidity (estimated from a thermodynamic model) indicated that preferable sulfate formation was related to low pH conditions, while high pH conditions promote nitrate formation. Data in different mass fraction ranges of alkaline metal ions showed that in some ranges the role of NH3 was replaced by alkaline metal ions in the neutralization reaction of H2SO4 and HNO3 to form particulate SO42- and NO3-. The relationships between mass fractions of SO42- and NO3- in those ranges of different alkaline metal ion content also suggested that alkaline metal ions participate in the competing neutralization reaction of sulfate and nitrate. The implication of the current study is that in some regions the chemistry to incorporate sulfur and nitrogen into particle phase might be largely affected by desert/fugitive dust and sea salt, besides NH3. This implication is particularly relevant in coastal China and those areas with strong influence of dust storm in the North China Plain (NCP), both of which host a number of megacities with deteriorating air quality.

Investigation of global particulate nitrate from the AeroCom phase III experiment

Article

Full-text available

Nov 2017
ATMOS CHEM PHYS

An assessment of global particulate nitrate and ammonium aerosol based on simulations from nine models participating in the Aerosol Comparisons between Observations and Models (AeroCom) phase III study is presented. A budget analysis was conducted to understand the typical magnitude, distribution, and diversity of the aerosols and their precursors among the models. To gain confidence regarding model performance, the model results were evaluated with various observations globally, including ground station measurements over North America, Europe, and east Asia for tracer concentrations and dry and wet depositions, as well as with aircraft measurements in the Northern Hemisphere mid-to-high latitudes for tracer vertical distributions. Given the unique chemical and physical features of the nitrate occurrence, we further investigated the similarity and differentiation among the models by examining (1) the pH-dependent NH3 wet deposition; (2) the nitrate formation via heterogeneous chemistry on the surface of dust and sea salt particles or thermodynamic equilibrium calculation including dust and sea salt ions; and (3) the nitrate coarse-mode fraction (i.e., coarse/total). It is found that HNO3, which is simulated explicitly based on full O3-HOx-NOx-aerosol chemistry by all models, differs by up to a factor of 9 among the models in its global tropospheric burden. This partially contributes to a large difference in NO3−, whose atmospheric burden differs by up to a factor of 13. The atmospheric burdens of NH3 and NH4+ differ by 17 and 4, respectively. Analyses at the process level show that the large diversity in atmospheric burdens of NO3−, NH3, and NH4+ is also related to deposition processes. Wet deposition seems to be the dominant process in determining the diversity in NH3 and NH4+ lifetimes. It is critical to correctly account for contributions of heterogeneous chemical production of nitrate on dust and sea salt, because this process overwhelmingly controls atmospheric nitrate production (typically > 80 %) and determines the coarse- and fine-mode distribution of nitrate aerosol.

Investigation of global nitrate from the AeroCom Phase III experiment

Article

Full-text available

May 2017
ACP

An assessment of global nitrate and ammonium aerosol based on simulations from nine models participating in the AeroCom Phase III study is presented. A budget analyses was conducted to understand the typical magnitude, distribution, and diversity of the aerosols and their precursors among the models. To gain confidence on model performance, the model results were evaluated with various observations globally, including ground station measurements over North America, Europe, and East Asia for tracer concentrations and dry and wet depositions, as well as with aircraft measurements in the Northern Hemisphere mid-high latitudes for tracer vertical distributions. Given the unique chemical and physical features of the nitrate occurrence, we further investigated the similarity and differentiation among the models by examining: (1) the pH-dependent NH3 wet deposition; (2) the nitrate formation via heterogeneous chemistry on the surface of dust and sea-salt particles; and (3) the nitrate coarse mode fraction (i.e., coarse/total). It is found that HNO3, which is simulated explicitly based on full O3–HOx–NOx–aerosol chemistry by all models, differs by up to a factor of 9 among the models in its global tropospheric burden. This partially contributes to a large difference in NO3−, whose atmospheric burden differs by up to a factor of 13. Analyses at the process level show that the large diversity in atmospheric burdens of NO3−, NH3, and NH4⁺ is also related to deposition processes. Wet deposition seems to be the dominant process in determining the diversity in NH3 and NH4⁺ lifetimes. It is critical to correctly account for contributions of heterogeneous chemical production of nitrate on dust and sea-salt, because this process overwhelmingly controls atmospheric nitrate production (typically > 80 %) and determines the coarse and fine mode distribution of nitrate aerosol.

Summertime PM2.5 ionic species in four major cities of China: nitrate formation in an ammonia-deficient atmosphere

Article

Full-text available

Jun 2008
ACP

Strong atmospheric photochemistry in summer can produce a significant amount of secondary aerosols, which may have a large impact on regional air quality and visibility. In the study reported herein, we analyzed sulfate, nitrate, and ammonium in PM2.5 samples collected using a 24-h filter system at suburban and rural sites near four major cities in China (Beijing, Shanghai, Guangzhou, and Lanzhou). Overall, the PM2.5 mass concentrations were high (with a mean value of 55–68 µg m−3), which reflects the long-known particulate pollution in China's large urban centers. We observed very high concentrations of sulfate and nitrate at the Beijing and Shanghai sites, and, in particular, abnormally high levels of nitrate (24-h average concentration up to 42 µg m−3 and contributing up to 25% of the PM2.5 mass) in the ammonium-poor samples. The Beijing and Shanghai aerosols were characterized by high levels of aerosol acidity (~220–390 nmol m−3) and low levels of in-situ pH (−0.77 to −0.52). In these samples, the formation of the observed high concentrations of particulate nitrate cannot be explained by homogeneous gas-phase reaction between ammonia and nitric acid. Examination of the relation of nitrate to relative humidity and aerosol loading suggests that the nitrate was most probably formed via the heterogeneous hydrolysis of N2O5 on the surface of the moist and acidic aerosols in Beijing and Shanghai. In comparison, the samples collected in Lanzhou and Guangzhou were ammonium-rich with low levels of aerosol acidity (~65–70 nmol m−3), and the formation of ammonium nitrate via the homogeneous gas-phase reaction was favored, which is similar to many previous studies. An empirical fit has been derived to relate fine nitrate to aerosol acidity, aerosol water content, aerosol surface area, and the precursor of nitrate for the data from Beijing and Shanghai.

Development of an Automated System (PPWD/PILS) for Studying PM 2.5 Water-Soluble Ions and Precursor Gases: Field Measurements in Two Cities, Taiwan

Article

Dec 2016

An automated system consisting of a particle-into-liquid sampler (PILS) and a parallel plate wet denuder (PPWD) coupled with an ion chromatography was used for simultaneous measurement of ambient water-soluble ions in PM 2.5 and precursor gases. The performance of the PPWD/PILS was validated by comparing it with the PDS (porous metal denuder sampler) for precursor gases (NH 3 , HONO, HNO 3 and SO 2) and PM 2.5 ionic species (NH 4 + , NO 3 – , SO 4 2– , Na + , Cl – and K +) measured in Taipei and Hsinchu Cities of Taiwan. Good correlations were demonstrated with linear regression slopes ranging from 0.92 to 1.04 and 0.84 to 0.97 as well as R 2 ranging from 0.76 to 0.83 and 0.89 to 0.94, for precursor gases and PM 2.5 ions, respectively. The accuracy of the current system for precursor gases outperforms the other commercial systems. Field continuous data showed that NH 3 was the most abundant precursor gas with the diurnal pattern peaking at low nocturnal boundary heights and during rush hours with local traffic emissions in Taipei, and with the pattern peaking only at midday associated with regional sources in Hsinchu. A reverse diurnal pattern for HONO in Taipei reflected the daytime photolysis and its nocturnal heterogeneous reaction, while its concentration was relatively constant at very low level in Hsinchu. SO 4 2– , NH 4 + and NO 3 – exhibited very similar diurnal patterns with the mean concentrations of 4.56 ± 3.14, 1.55 ± 1.16 and 0.52 ± 0.5 µg m –3 in Taipei, and 7.95 ± 5.52, 2.41 ± 1.95 and 0.96 ± 1.10 µg m –3 in Hsinchu, respectively. Correspondingly high concentrations of major ions to precursor gases were associated with the photochemical secondary aerosol formations and heavy traffic in Taipei. Based on an ammonia-rich atmosphere and high SOR values, (NH 4) 2 SO 4 and NH 4 NO 3 were inferred to be the dominant inorganic salts in PM 2.5 at both sites, which were also verified by the ion balance analysis.

Enhanced concentrations of reactive nitrogen species in wildfire smoke

Article

Oct 2016
ATMOS ENVIRON

During the summer of 2012 the Hewlett Gulch and High Park wildfires burned an area of 400 km² northwest of Fort Collins, Colorado. These fires both came within 20 km of the Department of Atmospheric Science at Colorado State University, allowing for extensive measurements of smoke-impacted air masses over the course of several weeks. In total, smoke plumes were observed at the measurement site for approximately 125 h. During this time, measurements were made of multiple reactive nitrogen compounds, including gas phase species NH3, NOx, and HNO3, and particle phase species NO3⁻ and NH4⁺, plus an additional, unspeciated reactive nitrogen component that is measured by high temperature conversion over a catalyst to NO. Concurrent measurements of CO, levoglucosan and PM2.5 served to confirm the presence of smoke at the monitoring site. Significant enhancements were observed for all of the reactive nitrogen species measured in the plumes, except for NH4⁺ which did not show enhancements, likely due to the fresh nature of the plume, the presence of sufficient regional ammonia to have already neutralized upwind sulfate, and the warm conditions of the summer measurement period which tend to limit ammonium nitrate formation. Excess mixing ratios for NH3 and NOx relative to excess mixing ratios of CO in the smoke plumes, ΔNH3/ΔCO (ppb/ppb) and ΔNOx/ΔCO (ppb/ppb), were determined to be 0.027 ± 002 and 0.0057 ± 0.0007, respectively. These ratios suggest that smoldering combustion was the dominant source of smoke during our plume interceptions. Observations from prior relevant laboratory and field measurements of reactive nitrogen species are also briefly summarized to help create a more comprehensive picture of reactive nitrogen and fire.

How much is particulate matter near the ground influenced by upper level processes within and above the PBL? A summertime case study in Milan (Italy)

Article

Full-text available

Oct 2014
ACP

Chemical and dynamical processes yield to the formation of aerosol layers in the upper planetary boundary layer (PBL) and above it. Through vertical mixing and entrainment into the PBL these layers may contribute to the ground-level particulate matter (PM), but a quantitative assessment of such contribution is still missing. This study investigates this aspect combining chemical and physical aerosol measurements with WRF/Chem model simulations. The observations were collected in the Milan urban area (Northern Italy) during summer of 2007. The period coincided with the passage of a meteorological perturbation that cleansed the lower atmosphere, followed by a high pressure period that favoured pollutant accumulation. Lidar observations reveal the formation of elevated aerosol layers and show evidences of their entrainment into the PBL. We analyze the budget of ground-level PM2.5 (particulate matter with aerodynamic diameter less than 2.5 μm with the help of the online meteorology-chemistry WRF/Chem model, with particular focus on the contribution of upper level processes. We find that an important player in determining the upper PBL aerosol layer is particulate nitrate, which may reach higher values in the upper PBL (up to 30% of the aerosol mass) than the lower. The nitrate formation process is predicted to be largely driven by the relative humidity vertical profile, that may trigger efficient aqueous nitrate formation when exceeding the ammonium nitrate deliquescence point. Secondary PM2.5 produced in the upper half of the PBL may contribute up to 7–8 μg m−3 (or 25%) to ground level concentrations on hourly basis. A large potential role is also found to be played by the residual aerosol layer above the PBL, which may occasionally contribute up to 10–12 μg m−3 (or 40%) to hourly ground level PM2.5 concentrations during the morning. This study highlights the importance of considering the interplay between chemical and dynamical processes occurring within and above the PBL when interpreting ground level aerosol observations.

Comparisons of urban and rural PM10−2.5 and PM2.5 mass concentrations and semi-volatile fractions in northeastern Colorado

Article

Full-text available

Jun 2016
ATMOS CHEM PHYS

Coarse (PM10−2.5) and fine (PM2.5) particulate matter in the atmosphere adversely affect human health and influence climate. While PM2.5 is relatively well studied, less is known about the sources and fate of PM10−2.5. The Colorado Coarse Rural-Urban Sources and Health (CCRUSH) study measured PM10−2.5 and PM2.5 mass concentrations, as well as the fraction of semi-volatile material (SVM) in each size regime (SVM2.5, SVM10−2.5), from 2009 to early 2012 in Denver and comparatively rural Greeley, Colorado. Agricultural operations east of Greeley appear to have contributed to the peak PM10−2.5 concentrations there, but concentrations were generally lower in Greeley than in Denver. Traffic-influenced sites in Denver had PM10−2.5 concentrations that averaged from 14.6 to 19.7 µg m−3 and mean PM10−2.5 ∕ PM10 ratios of 0.56 to 0.70, higher than at residential sites in Denver or Greeley. PM10−2.5 concentrations were more temporally variable than PM2.5 concentrations. Concentrations of the two pollutants were not correlated. Spatial correlations of daily averaged PM10−2.5 concentrations ranged from 0.59 to 0.62 for pairs of sites in Denver and from 0.47 to 0.70 between Denver and Greeley. Compared to PM10−2.5, concentrations of PM2.5 were more correlated across sites within Denver and less correlated between Denver and Greeley. PM10−2.5 concentrations were highest during the summer and early fall, while PM2.5 and SVM2.5 concentrations peaked in winter during periodic multi-day inversions. SVM10−2.5 concentrations were low at all sites. Diurnal peaks in PM10−2.5 and PM2.5 concentrations corresponded to morning and afternoon peaks of traffic activity, and were enhanced by boundary layer dynamics. SVM2.5 concentrations peaked around noon on both weekdays and weekends. PM10−2.5 concentrations at sites located near highways generally increased with wind speeds above about 3 m s−1. Little wind speed dependence was observed for the residential sites in Denver and Greeley. The mass concentration data reported here are being used in ongoing epidemiologic studies for PM in northeastern Colorado.

Increasing importance of deposition of reduced nitrogen in the United States

Article

Full-text available

May 2016

Significance Human activities have greatly increased emissions of reactive forms of nitrogen to the atmosphere. This perturbation to the nitrogen cycle has produced large increases of nitrogen deposition to sensitive ecosystems. Over recent decades, attention has focused on wet and dry deposition of nitrate stemming from fossil fuel combustion emissions of nitrogen oxides. Successful decreases in nitrogen oxides emissions in the United States have substantially decreased nitrate deposition. By contrast, emissions of ammonia, an unregulated air pollutant, and resulting deposition of ammonium have grown. Expanded observations demonstrate that deposition of reactive nitrogen in the United States has shifted from a nitrate-dominated to an ammonium-dominated condition. Recognition of this shift is critical to formulating effective future policies to protect ecosystems from excess nitrogen deposition.

On the Interplay Between Upper and Ground Levels Dynamics and Chemistry in Determining the Surface Aerosol Budget

Chapter

Full-text available

Mar 2014

We use the WRF/Chem model to interpret observations of the aerosol concentration and its chemical composition both at surface level and along vertical profiles performed during an intensive campaign in July 2007 in Milan urban area. The model is added with a new diagnostic for aerosol budget analysis, building on that available for gas species, in order to study the contribution of upper levels processes on the aerosol formation at ground level. The analysis illustrates a quite variegated evolution of budget terms, which we found to depend strongly on the hour of the day, the vertical level, the aerosol compound, and the aerosol size. Primary components are generally emitted near the ground and rapidly transported by turbulent motions to the upper levels, where they gradually disperse and age. For some secondary components, such as nitrate, we calculate a net chemical destruction in the bottom layers, as opposed to a net chemical production higher in the boundary layer, which supply new material to ground level aerosol through turbulent mixing.

Organic nitrate aerosol formation via NO3 + biogenic volatile organic compounds in the southeastern United States

Article

Full-text available

Dec 2015
ATMOS CHEM PHYS

Gas- and aerosol-phase measurements of oxidants, biogenic volatile organic compounds (BVOCs) and organic nitrates made during the Southern Oxidant and Aerosol Study (SOAS campaign, Summer 2013) in central Alabama show that a nitrate radical (NO3) reaction with monoterpenes leads to significant secondary aerosol formation. Cumulative losses of NO3 to terpenes are correlated with increase in gas- and aerosol-organic nitrate concentrations made during the campaign. Correlation of NO3 radical consumption to organic nitrate aerosol formation as measured by aerosol mass spectrometry and thermal dissociation laser-induced fluorescence suggests a molar yield of aerosol-phase monoterpene nitrates of 23–44 %. Compounds observed via chemical ionization mass spectrometry (CIMS) are correlated to predicted nitrate loss to BVOCs and show C10H17NO5, likely a hydroperoxy nitrate, is a major nitrate-oxidized terpene product being incorporated into aerosols. The comparable isoprene product C5H9NO5 was observed to contribute less than 1 % of the total organic nitrate in the aerosol phase and correlations show that it is principally a gas-phase product from nitrate oxidation of isoprene. Organic nitrates comprise between 30 and 45 % of the NOy budget during SOAS. Inorganic nitrates were also monitored and showed that during incidents of increased coarse-mode mineral dust, HNO3 uptake produced nitrate aerosol mass loading at a rate comparable to that of organic nitrate produced via NO3 + BVOCs.

The spatial distribution of reactive nitrogen species and nitrogen deposition in Grand Teton National Park

Article

Simulation of the aerosol direct radiative forcing over Europe

Article

Nov 2010

J. C. Péré

The main objective of this work was to estimate the direct radiative forcing of polluted aerosols during the heat wave of summer 2003 over Western Europe. A particular interest was focused on studying the possible feedbacks of this aerosol direct radiative forcing on the atmospheric dynamic and photochemical processes. First, an optical scheme dedicated to calculate optical properties of particles, for three types of aerosol mixing (external, internally homogeneous and core-shell) was developed into the chemistry-transport model CHIMERE. An evaluation of the optical module was performed for all the year 2003 based on optical properties retrieved by photometers and satellite sensors. Then, different couplings between the CHIMERE model (associated with the optical module), the meteorological model WRF and the radiative transfert code TUV, were used to evaluate the aerosol direct radiative forcing and its potential feedback on the atmospheric dynamic and photochemical processes.

Organic nitrate aerosol formation via NO3 + BVOC in the Southeastern US

Article

Full-text available

Jun 2015
ACP

Gas- and aerosol-phase measurements of oxidants, biogenic volatile organic compounds (BVOC) and organic nitrates made during the Southern Oxidant and Aerosol Study (SOAS campaign, Summer 2013) in central Alabama show that nitrate radical (NO3) reaction with monoterpenes leads to significant secondary aerosol formation. Cumulative losses of NO3 to terpenes are calculated and correlated to gas and aerosol organic nitrate concentrations made during the campaign. Correlation of NO3 radical consumption to organic nitrate aerosol as measured by Aerosol Mass Spectrometry (AMS) and Thermal Dissociation – Laser Induced Fluorescence (TD-LIF) suggests a range of molar yield of aerosol phase monoterpene nitrates of 23–44 %. Compounds observed via chemical ionization mass spectrometry (CIMS) are correlated to predicted nitrate loss to terpenes and show C10H17NO5, likely a hydroperoxy nitrate, is a major nitrate oxidized terpene product being incorporated into aerosols. The comparable isoprene product C5H9NO5 was observed to contribute less than 0.5 % of the total organic nitrate in the aerosol-phase and correlations show that it is principally a gas-phase product from nitrate oxidation of isoprene. Organic nitrates comprise between 30 and 45 % of the NOy budget during SOAS. Inorganic nitrates were also monitored and showed that during incidents of increased coarse-mode mineral dust, HNO3 uptake produced nitrate aerosol mass loading comparable to that of organic nitrate produced via NO3 + BVOC.

How much is particulate matter near the ground influenced by upper level processes within and above the PBL? A summertime case study in Milan (Italy)

Article

Full-text available

Mar 2015

Chemical and dynamical processes lead to the formation of aerosol layers in the upper planetary boundary layer (PBL) and above it. Through vertical mixing and entrainment into the PBL these layers may contribute to the ground-level particulate matter (PM); however, to date a quantitative assessment of such a contribution has not been carried out. This study investigates this aspect by combining chemical and physical aerosol measurements with WRF/Chem (Weather Research and Forecasting with Chemistry) model simulations. The observations were collected in the Milan urban area (northern Italy) during the summer of 2007. The period coincided with the passage of a meteorological perturbation that cleansed the lower atmosphere, followed by a high-pressure period favouring pollutant accumulation. Lidar observations revealed the formation of elevated aerosol layers and evidence of their entrainment into the PBL. We analysed the budget of ground-level PM2.5 (particulate matter with an aerodynamic diameter less than 2.5 μm) with the help of the online meteorology–chemistry WRF/Chem model, focusing in particular on the contribution of upper-level processes. Our findings show that an important player in determining the upper-PBL aerosol layer is particulate nitrate, which may reach higher values in the upper PBL (up to 30% of the aerosol mass) than in the lower PBL. The nitrate formation process is predicted to be largely driven by the relative-humidity vertical profile, which may trigger efficient aqueous nitrate formation when exceeding the ammonium nitrate deliquescence point. Secondary PM2.5 produced in the upper half of the PBL may contribute up to 7–8 μg m−3 (or 25%) to ground-level concentrations on an hourly basis. The residual aerosol layer above the PBL is also found to potentially play a large role, which may occasionally contribute up to 10–12 μg m−3 (or 40%) to hourly ground-level PM2.5 concentrations during the morning hours. Although the results presented here refer to one relatively short period in one location, this study highlights the importance of considering the interplay between chemical and dynamical processes occurring within and above the PBL when interpreting ground-level aerosol observations.

Overview of the LADCO winter nitrate study: hourly ammonia, nitric acid and PM2.5 composition at an urban and rural site pair during PM2.5 episodes in the US Great Lakes region

Article

Full-text available

Jun 2012
ACP

An overview of the LADCO (Lake Michigan Air Directors Consortium) Winter Nitrate Study (WNS) is presented. Sampling was conducted at ground level at an urban-rural pair of sites during January–March 2009 in eastern Wisconsin, toward the Western edge of the US Great Lakes region. Areas surrounding these sites experience multiday episodes of wintertime PM2.5 pollution characterized by high fractions of ammonium nitrate in PM, low wind speeds, and air mass stagnation. Hourly surface monitoring of inorganic gases and aerosols supplemented long-term 24-h aerosol chemistry monitoring at these locations. The urban site (Milwaukee, WI) experienced 13 PM2.5 episodes, defined as periods where the seven-hour moving average PM2.5 concentration exceeded 27 μg m−3 for at least four consecutive hours. The rural site experienced seven episodes by the same metric, and all rural episodes coincided with urban episodes. Episodes were characterized by low pressure systems, shallow/stable boundary layer, light winds, and increased temperature and relative humidity relative to climatological mean conditions. They often occurred in the presence of regional snow cover at temperatures near freezing, when snow melt and sublimation could generate fog and strengthen the boundary layer inversion. Substantial contribution to nitrate production from nighttime chemistry of ozone and NO2 to N2O5 and nitric acid is likely and requires further investigation. Pollutant-specific urban excess during episode and non-episode conditions is presented. The largest remaining uncertainties in the conceptual model of the wintertime episodes are the variability from episode-to-episode in ammonia emissions, the balance of daytime and nighttime nitrate production, the relationship between ammonia controls, NOx controls and ammonium nitrate reductions, and the extent to which snow and fog are causal (either through meteorological or chemical processes) rather than just correlated with episodes because of similar synoptic meteorology.

Considerations for realistic atmospheric environments: An application to corrosion testing

Article

Full-text available

May 2023
SCI TOTAL ENVIRON

Measured salt compositions in dust collected over roughly the last decade from surfaces of in-service stainless-steel alloys at four locations around the United States are presented, along with the predicted brine compositions that would result from deliquescence of these salts. The salt compositions vary greatly from ASTM seawater and from laboratory salts (i.e., NaCl or MgCl2) commonly used on corrosion testing. The salts contained relatively high amounts of sulfates and nitrates, evolved to basic pH values, and exhibited deliquescence relative humidity values (RH) higher than seawater. Additionally, inert dust components were quantified and considerations for laboratory testing with inert dust are presented. The observed environments are discussed in terms of the potential corrosion behavior and are compared to commonly used accelerated testing protocols. Finally, ambient weather conditions and their influence on diurnal fluctuations in temperature (T) and RH on heated metal surfaces are evaluated and a relevant diurnal cycle for laboratory testing a heated surface has been developed. Suggestions for future accelerated tests are proposed that include exploration of the effects of inert dust particles on atmospheric corrosion, chemistry considerations, and realistic diurnal fluctuations in T and RH. Understanding mechanisms in both realistic and accelerated environments will allow development of a corrosion factor (i.e., scaling factor) for the extrapolation of laboratory-scale test results to real world applications.

Wintertime haze and ozone at Dinosaur National Monument

Article

Mar 2022

Dinosaur National Monument (DINO) is located near the northeastern edge of the Uinta Basin and often experiences elevated levels of wintertime ground-level ozone. Previous studies have shown that high ozone mixing ratios in the Uinta Basin are driven by elevated levels of volatile organic compounds (VOCs) and nitrogen oxides (NOx) from regional oil and gas development coupled with temperature inversions and enhanced photochemistry from persistent snow cover. Here we show that persistent snow cover and temperature inversions, along with abundant ammonia, also lead to wintertime haze in this region. A study was conducted at DINO from November 2018 through May 2020 where ozone, speciated fine and coarse aerosols, inorganic gases, and VOCs were measured. Three National Ambient Air Quality Standards (NAAQS) ozone exceedances were observed in the first winter, and no exceedances were observed in the second winter. In contrast, elevated levels of particulate matter were observed both winters, with 24-h averaged particle light extinction exceeding 100 Mm-1. These haze events were dominated by ammonium nitrate, and particulate organics were highly correlated with ammonium nitrate. Ammonium nitrate formation was limited by nitric acid in winter. As such, reductions in regional NOx emissions should reduce haze levels and improve visibility at DINO in winter. Long-term measurements of particulate matter from nearby Vernal, Utah, suggest that visibility impairment is a persistent issue in the Uinta Basin in winter. From April through October 2019, relatively clean conditions occurred, with average particle extinction of ~10 Mm-1. During this period, ammonium nitrate concentrations were lower by more than an order of magnitude, and contributions from coarse mass and soil to haze levels increased. VOC markers indicated that the high levels of observed pollutants in winter were likely from local sources related to oil and gas extraction activities.

Evaluation of interactive and prescribed agricultural ammonia emissions for simulating atmospheric composition in CAM-chem

Article

Full-text available

Feb 2022
ATMOS CHEM PHYS

Ammonia (NH3) plays a central role in the chemistry of inorganic secondary aerosols in the atmosphere. The largest emission sector for NH3 is agriculture, where NH3 is volatilized from livestock wastes and fertilized soils. Although the NH3 volatilization from soils is driven by the soil temperature and moisture, many atmospheric chemistry models prescribe the emission using yearly emission inventories and climatological seasonal variations. Here we evaluate an alternative approach where the NH3 emissions from agriculture are simulated interactively using the process model FANv2 (Flow of Agricultural Nitrogen, version 2) coupled to the Community Atmospheric Model with Chemistry (CAM-chem). We run a set of 6-year global simulations using the NH3 emission from FANv2 and three global emission inventories (EDGAR, CEDS and HTAP) and evaluate the model performance using a global set of multi-component (atmospheric NH3 and NH4+, and NH4+ wet deposition) in situ observations. Over East Asia, Europe and North America, the simulations with different emissions perform similarly when compared with the observed geographical patterns. The seasonal distributions of NH3 emissions differ between the inventories, and the comparison to observations suggests that both FANv2 and the inventories would benefit from more realistic timing of fertilizer applications. The largest differences between the simulations occur over data-scarce regions. In Africa, the emissions simulated by FANv2 are 200 %–300 % higher than in the inventories, and the available in situ observations from western and central Africa, as well as NH3 retrievals from the Infrared Atmospheric Sounding Interferometer (IASI) instrument, are consistent with the higher NH3 emissions as simulated by FANv2. Overall, in simulating ammonia and ammonium concentrations over regions with detailed regional emission inventories, the inventories based on these details (HTAP, CEDS) capture the atmospheric concentrations and their seasonal variability the best. However these inventories cannot capture the impact of meteorological variability on the emissions, nor can these inventories couple the emissions to the biogeochemical cycles and their changes with climate drivers. Finally, we show with sensitivity experiments that the simulated time-averaged nitrate concentration in air is sensitive to the temporal resolution of the NH3 emissions. Over the CASTNET monitoring network covering the US, resolving the NH3 emissions hourly instead monthly reduced the positive model bias from approximately 80 % to 60 % of the observed yearly mean nitrate concentration. This suggests that some of the commonly reported overestimation of aerosol nitrate over the US may be related to unresolved temporal variability in the NH3 emissions.

Medical geochemistry of particulate matter and environmental impact associated with mining and mineral processing in Gol-E-Gohar (GEG) iron mine, Sirjan, Iran

Thesis

Apr 2017

Naghmeh Soltani

A major problem, especially in the arid and semi-arid areas of Gol-E-Gohar mining and industrial company in Kerman province, appears to be the contamination by dust fallout from mining operations, iron ore processing, and from tailing piles. For this purpose, 109 topsoil, 7 tailing, 60 plant (roots and leaves of Artemisia sieberi and zygophylum species), 10 fallout dust and 74 particulate matter in PM2.5, PM10, and TSP were collected and analyzed for PTE concentrations. The results of elements concentration in topsoil and plants indicate that the tailings, soil and plants near the iron ore mine are contaminated with PTEs and can be dispersed via aerosol transport and deposition. Particulate matter and fallout dust samples were characterized in terms of mass concentration, mineralogy, morphology, oxidative potential, oral bioaccessibility of PTEs, hygroscopic properties. Results of particulate matter mass concentration show that indoor samples exceeded the 24-h PM2.5 and PM10 mass concentration limits (35 µg m-3 and 150 µg m-3, respectively) set by the US National Ambient Air Quality Standards as well as the 24-hour mean guideline values established by the World Health Organization (25 µg m-3 for PM2.5 and 50 µg m-3 for PM10). The results of mineralogical studies by XRD and SEM/EDS show that the presence of minerals related to respiratory diseases, such as talc, crystalline silica, and needle-shaped minerals like amphibole asbestos (tremolite and actinolite), strongly suggests the need for detailed health-based studies in the region. The PM oxidative potential per volume of air is exceptionally high, confirming that the workers are exposed to a considerable oxidative environment. The Unified Bioaccessibility Method (UBM), which simulates the fluids of the human gastrointestinal tract, was used to assess the oral bioaccessibility of As, Cd, Cu, Co, Fe, Ni, and Pb in fallout dusts. The oral bioaccessibility of Cu, Co, Fe, and Ni were typically greater in the ‘stomach’ (pH ~1.2) compared with the ‘stomach+intestine’ (pH ~6.3) simulation. For assessing hygroscopic properties of particulate matter, samples were examined with ion chromatography, and a humidified tandem differential mobility analyzer with a focus on how hygroscopic growth impacts particle deposition behavior in different parts of human lung. The results of PTE concentrations examined by ICP-MS in particulate matter collected at the measurement site are enriched in metals and metalloids (e.g., iron, copper, cobalt, arsenic, vanadium, and nickel) and water uptake measurements of aqueous extracts of collected samples indicate that TSP enriched with these species overlaps with the most hygroscopic mode at a relative humidity of 90%. PM released by iron ore mining and processing activities should be considered a potential health risk to the mine workers and nearby employees and strategies to combat the issue are suggested.

Evolution of secondary inorganic aerosols amidst improving PM2.5 air quality in the North China Plain

Article

Mar 2021
ENVIRON POLLUT

The Clean Air Action implemented by the Chinese government in 2013 has greatly improved air quality in the North China Plain (NCP). In this work, we report changes in the chemical components of atmospheric fine particulate matter (PM2.5) at four NCP sampling sites from 2012/2013 to 2017 to investigate the impacts and drivers of the Clean Air Action on aerosol chemistry, especially for secondary inorganic aerosols (SIA). During the observation period, the concentrations of PM2.5 and its chemical components (especially SIA, organic carbon (OC), and elemental carbon (EC)) and the frequency of polluted days (daily PM2.5 concentration ≥ 75 μg m⁻³) in the NCP, declined significantly at all four sites. Asynchronized reduction in SIA components (large decreases in SO4²⁻ with stable or even increased NO3⁻ and NH4⁺) was observed in urban Beijing, revealing a shift of the primary form of SIA, which suggested the fractions of NO3⁻ increased more rapidly than SO4²⁻ during PM2.5 pollution episodes, especially in 2016 and 2017. In addition, unexpected increases in the sulfur oxidation ratio (SOR) and the nitrogen oxidation ratio (NOR) were observed among sites and across years in the substantially decreased PM2.5 levels. They were largely determined by secondary aerosol precursors (i.e. decreased SO2 and NO2), photochemical oxidants (e.g. increased O3), temperature, and relative humidity via gas-phase and heterogeneous reactions. Our results not only highlight the effectiveness of the Action Plan for improving air quality in the NCP, but also suggest an increasing importance of SIA in determining PM2.5 concentration and composition.

Influence of crustal dust and sea spray supermicron particle concentrations and acidity on inorganic NO3− aerosol during the 2013 southern oxidant and aerosol study

Article

Jan 2015

Enhancement of dry deposition of PM2.5 nitrate in a cool-temperate forest

Article

May 2019
ATMOS ENVIRON

Fine particulate matter (PM2.5) is one of most concerning air pollutants in East Asia. In order to further understand the dry deposition process of PM2.5, measurements were carried out in a cool-temperate forest located in a remote area of northern Japan. These measurements took into account the improvement of simulations by chemical transport models in this region. We measured the vertical profiles of fine (PM2.5), coarse aerosol components, HNO3, and other relevant gases using two denuder/filter-pack sampling systems together with three 4-stage filter-pack sampling systems from July 22, 2017 to August 07, 2017. The vertical profile measurements clearly showed the difference in dry deposition process between fine NO3⁻ and fine SO4²⁻. Concentration gradients of fine NO3⁻ from over to under the canopy were significantly higher than those of fine SO4²⁻. Since most of fine NO3⁻ existed as NH4NO3, it was considered that these high gradients of NO3⁻ were associated with the process of the conversion between NH4NO3 and HNO3/NH3. The concentration gradients of fine NO3⁻ increased with the increase in daytime air temperature from over to under the canopy. The simulations of the thermodynamic equilibrium of NH4NO3 at canopy surface temperatures using ISORROPIA II showed that the equilibrium shift of NH4NO3 into the gas phase during the daytime hot canopy can decrease fine NO3⁻ by approximately 9% when compared to normal atmospheric conditions. The volatilized HNO3 was most probably immediately removed by the canopy as the HNO3 concentrations near the canopy were extremely low. Therefore, the equilibrium shift enhanced the dry deposition of nitrogen within fine NO3⁻.

The impact of sea-salt aerosols on particulate inorganic nitrogen deposition in the western Taiwan Strait region, China

Article

May 2019
ATMOS RES

Sea-salt aerosol (SSA) has significant impact on the formation of secondary nitrate and its dry deposition in the coastal region. In this study, size-segregated aerosols were collected for water-soluble ions analysis in the coastal cities and sea cruises in the western Taiwan Strait of China from 2016 to 2017 to investigate the impact of SSA on particulate inorganic N deposition. The size distributions of NH4⁺ were characterized by a unimodal pattern peaking at 0.44–1.0 μm while NO3⁻ exhibited typical bimodal distributions peaking at 0.44–1.0 μm and 2.5–10 μm. Furthermore, the fine mode peaks of NO3⁻ became insignificant or disappeared in summer and fall due to the volatilization and dissociation of NH4NO3 at higher temperatures. Elevated sea-salt contributions in the largest size bin (>16 μm) during sea cruises were attributed to vessel induced wave breaking, while there was no peak for NO3⁻ at this range due to its short atmospheric lifetime. Although the concentrations of particulate NH4⁺-N showed higher levels than those of NO3⁻-N for both coastal and marine aerosols, the dry deposition fluxes of the particulate NO3⁻-N were significant higher than those of the particulate NH4⁺-N due to their different size distributions. The contribution of SSA to particulate inorganic N deposition was estimated on average to be 20.33% and 36.91% in the coastal and offshore region, respectively, assuming all of the chlorine depletion was caused by the reaction between nitric acid and SSA in the coarse mode. In addition, dry deposition fluxes using constant deposition velocities for fine/coarse particles and NH4⁺/NO3⁻ were higher than those using size-dependent dry deposition velocities. Considering the increasing human activities at the coastal urban zone in the western Taiwan Strait, the atmospheric N deposition could have an important ecological impact on the marine environment that is already under pressure from riverine inputs and urban waste discharges.

Size-resolved Characteristics of Water-Soluble Particulate Elements in a Coastal Area: Source Identification, Influence of Wildfires, and Diurnal Variability

Article

Mar 2019
ATMOS ENVIRON

Size-resolved elemental measurements were conducted for the water-soluble fraction of particulate matter at a central California coastal city, Marina, during two separate summertime field campaigns: the Nucleation in California Experiment (NiCE) in 2013 and the Fog and Stratocumulus Evolution (FASE) campaign in 2016. Two Micro-Orifice Uniform Deposit Impactors (MOUDIs) were used to quantify mass size distributions of 29 elements and a Positive Matrix Factorization (PMF) model revealed six characteristic sources during the measurement periods: (i) Crustal Emissions (3.9% of total mass), (ii) Secondary Aerosol (24.4%), (iii) Biomass Burning (13.1%), (iv) Waste Facilities (8.7%), (v) Vehicular Emissions (4.4%), and (vi) Marine Emissions (45.4%). Characteristic elements from each of these sources included the following: (i) Crustal Emissions (Fe, Al, Ti, Pt), (ii) Secondary Aerosol (Zn, As, Rb, K, Cu, V), (iii) Biomass Burning (Rb, K, Cu, Pt), (iv) Waste Facilities (Ag, Cd, Ni, Al), (v) Vehicular Emissions (Zn, Zr, V, Mn), and (vi) Marine Emissions (Na, Sr, V, Mn). Temporally-resolved results revealed higher PM levels associated with Vehicular Emissions (day/night mass concentration ratio = 31.3), Crustal Emissions (day/night = 20.0), and Secondary Aerosol (day/night = 27.2) during the day compared to night due to some combination of more daytime anthropogenic activity, wind speed/directional factors, and photochemistry. The Marine Emissions factor exhibited a day/night concentration ratio of exactly 1.0. Mass size distributions revealed characteristic peaks in four diameter ranges: 0.1–0.18 μm, 0.32–0.56 μm, 1.0–1.8 μm, and 3.2–5.6 μm. The number of modes varied depending on the species and degree of wildfire influence, with additional differences observed between the NiCE and FASE wildfire periods.

Trends in remote PM2.5 residual mass across the United States: Implications for aerosol mass reconstruction in the IMPROVE network

Article

Apr 2019
ATMOS ENVIRON

The Interagency Monitoring of Protected Visual Environments (IMPROVE) network collects aerosol samples for gravimetric and composition analysis in support of the Environmental Protection Agency's Regional Haze Rule and for long-term trend studies and model evaluations. Reconstructing PM 2.5 mass or extinction from composition measurements requires assumptions of the molecular form of the individual species assumed to compose the bulk of PM 2.5 mass. The IMPROVE reconstruction algorithm includes sulfate as ammonium sulfate, nitrate as ammonium nitrate, organic mass calculated with an assumed organic carbon (OC) to organic mass (OM) multiplier (OM/OC) of 1.8, elemental carbon, fine dust assuming common mineral oxides in soil, and sea salt calculated from chloride. Comparisons of reconstructed fine mass (RCFM) to PM 2.5 gravimetric fine mass (FM) provide a check on these assumptions as well as help identify possible biases in gravimetric or speciated measurements. Significant changes in aerosol concentration and composition have occurred over time, leading to decreased FM across the United States. However, within the IMPROVE network, annual mean FM and RCFM have decreased at different rates from 2005 through 2016 (−29% versus −43%, respectively), causing the network median residuals (FM − RCFM) to increase by 0.49 μg m ⁻³ over the 12-year period. The residual shifted from mostly negative before 2011 to mostly positive after 2011, with a strong summer peak. A multiple linear regression analysis indicated that FM biases increased due to the presence of particle-bound water (PBW) after 2011, associated with increased laboratory relative humidity during weighing. Results also suggested that the OM/OC ratio increased across the network after 2011, unrelated to the influence of PBW. While temporal behavior in the OM/OC ratio was similar across the network and for all seasons, values were highest in the East and during summer. Fine dust also appeared to be underestimated by ∼20%. Identifying the source of the trends in the FM residual is essential for accurately estimating contributions by individual species to RCFM and visibility degradation.

Observation of Secondary Organic Aerosol and New Particle Formation at a Remote Site in Baengnyeong Island, Korea

Article

Dec 2017

To improve the understanding of secondary organic aerosol (SOA) formation from the photo-oxidation of anthropogenic and biogenic precursors at the regional background station on Baengnyeong Island, Korea, gas phase and aerosol chemistries were investigated using the Proton Transfer Reaction Time of Flight Mass Spectrometer (PTR-ToF-MS) and the Aerodyne High Resolution Time of Flight Aerosol Mass Spectrometer (HR-ToF-AMS), respectively. HR-ToF-AMS measured fine particles (PM1; diameter of particle matter less than 1 μm) at a 6-minute time resolution from February to November 2012, while PTR-ToF-MS was deployed during an intensive period from September 21 to 29, 2012. The one-minute time-resolution and high mass resolution (up to 4000 m Δm⁻¹) data from the PTR-ToF-MS provided the basis for calculations of the concentrations of anthropogenic and biogenic volatile organic compounds (BVOCs) including oxygenated VOCs (OVOCs). The dominant BVOCs from the site are isoprene (0.23 ppb), dimethyl sulphide (DMS, 0.20 ppb), and monoterpenes (0.38 ppb). Toluene (0.45 ppb) and benzene (0.32 ppb) accounted for the majority of anthropogenic VOCs (AVOCs). OVOCs including acetone (3.98 ppb), acetaldehyde (2.67 ppb), acetic acid (1.68 ppb), and formic acid (2.24 ppb) were measured. The OVOCs comprise approximately 75% of total measured VOCs, suggesting the occurrence of strong oxidation processes and/or long-range transported at the site. A strong photochemical aging and oxidation of the atmospheric pollutants were also observed in aerosol measured by HR-ToF-AMS, whereby a high f44: f43 value is shown for organic aerosols (OAs); however, relatively low f44: f43 values were observed when high concentrations of BVOCs and AVOCs were available, providing evidence of the formation of SOA from VOC precursors at the site. Overall, the results of this study revealed several different SOA formation mechanisms, and new particle formation and particle growth events were identified using the powerful tools scanning mobility particle sizer (SMPS), PTR-ToF-MS, and HR-ToF-AMS.

Simulating emission and chemical evolution of coarse sea-salt particles in the Community Multiscale Air Quality (CMAQ) model

Article

Full-text available

Dec 2009
GMDD

Chemical processing of sea-salt particles in coastal environments significantly impacts concentrations of particle components and gas-phase species and has implications for human exposure to particulate matter and nitrogen deposition to sensitive ecosystems. Emission of sea-salt particles from the coastal surf zone is known to be elevated compared to that from the open ocean. Despite the importance of sea-salt emissions and chemical processing, the US EPA's Community Multiscale Air Quality (CMAQ) model has traditionally treated coarse sea-salt particles as chemically inert and has not accounted for enhanced surf-zone emissions. In this article, updates to CMAQ are described that enhance sea-salt emissions from the coastal surf zone and allow dynamic transfer of HNO3, H2SO4, HCl, and NH3 between coarse particles and the gas phase. Predictions of updated CMAQ models and the previous release version, CMAQv4.6, are evaluated using observations from three coastal sites during the Bay Regional Atmospheric Chemistry Experiment (BRACE) in Tampa, FL in May 2002. Model updates improve predictions of NO3−, SO42−, NH4+, Na+, and Cl− concentrations at these sites with only a 8% increase in run time. In particular, the chemically interactive coarse particle mode dramatically improves predictions of nitrate concentration and size distributions as well as the fraction of total nitrate in the particle phase. Also, the surf-zone emission parameterization improves predictions of total sodium and chloride concentration. Results of a separate study indicate that the model updates reduce the mean absolute error of nitrate predictions at coastal CASTNET and SEARCH sites in the eastern US. Although the new model features improve performance relative to CMAQv4.6, some persistent differences exist between observations and predictions. Modeled sodium concentration is biased low and causes under-prediction of coarse particle nitrate. Also, CMAQ over-predicts geometric mean diameter and standard deviation of particle modes at the BRACE sites. These over-predictions may cause too rapid particle dry deposition and partially explain the low bias in sodium predictions. Despite these shortcomings, the updates to CMAQ enable more realistic simulations of chemical processes in environments where marine air mixes with urban pollution. The model updates described in this article are included in the public release of CMAQv4.7 (http://www.cmaq-model.org).

Composition and sources of winter haze in the Bakken oil and gas extraction region

Article

Full-text available

Feb 2017
ATMOS ENVIRON

In the past decade increased use of hydraulic fracturing and horizontal drilling has dramatically expanded oil and gas production in the Bakken formation region. Long term monitoring sites have indicated an increase in wintertime aerosol nitrate and sulfate in this region from particulate matter (PM2.5) measurements collected between 2000 and 2010. No previous intensive air quality field campaign has been conducted in this region to assess impacts from oil and gas development on regional fine particle concentrations. The research presented here investigates wintertime PM2.5 concentrations and composition as part of the Bakken Air Quality Study (BAQS). Measurements from BAQS took place over two wintertime sampling periods at multiple sites in the United States portion of the Bakken formation and show regionally elevated episodes of PM2.5 during both study periods. Ammonium nitrate was a major contributor to haze episodes. Periods of air stagnation or recirculation were associated with rapid increases in PM2.5 concentrations. Volatile organic compound (VOC) signatures suggest that air masses during these episodes were dominated by emissions from the Bakken region itself. Formation rates of alkyl nitrates from alkanes revealed an air mass aging timescale of typically less than a day for periods with elevated PM2.5. A thermodynamic inorganic aerosol model (ISORROPIA) was used to investigate gas-particle partitioning and to examine the sensitivity of PM2.5 concentrations to aerosol precursor concentrations. Formation of ammonium nitrate, the dominant component, was most sensitive to ammonia concentrations during winter and to nitric acid concentrations during early spring when ammonia availability increases. The availability of excess ammonia suggests capacity for further ammonium nitrate formation if nitrogen oxide emissions increase in the future and lead to additional secondary formation of nitric acid.

Development of an on-line source-tagged model for sulfate, nitrate and ammonium: A modeling study for highly polluted periods in Shanghai, China

Article

Dec 2016

An on-line source-tagged model coupled with an air quality model (Nested Air Quality Prediction Model System, NAQPMS) was applied to estimate source contributions of primary and secondary sulfate, nitrate and ammonium (SNA) during a representative winter period in Shanghai. This source-tagged model system could simultaneously track spatial and temporal sources of SNA, which were apportioned to their respective primary precursors in a simulation run. The results indicate that in the study period, local emissions in Shanghai accounted for over 20% of SNA contributions and that Jiangsu and Shandong were the two major non-local sources. In particular, non-local emissions had higher contributions during recorded pollution periods. This suggests that the transportation of pollutants plays a key role in air pollution in Shanghai. The temporal contributions show that the emissions from the "current day" (emission contribution from the current day during which the model was simulating) contributed 60%-70% of the sulfate and ammonium concentrations but only 10%-20% of the nitrate concentration, while the previous days' contributions increased during the recorded pollution periods. Emissions that were released within three days contributed over 85% averagely for SNA in January 2013. To evaluate the source-tagged model system, the results were compared by sensitivity analysis (emission perturbation of -30%) and backward trajectory analysis. The consistency of the comparison results indicated that the source-tagged model system can track sources of SNA with reasonable accuracy.

Aerosol and precipitation chemistry in the southwestern United States: spatiotemporal trends and interrelationships

Article

Full-text available

Apr 2013
ACP

This study characterizes the spatial and temporal patterns of aerosol and precipitation composition at six sites across the United States Southwest between 1995 and 2010. Precipitation accumulation occurs mostly during the wintertime (December–February) and during the monsoon season (July–September). Rain and snow pH levels are usually between 5–6, with crustal-derived species playing a major role in acid neutralization. These species (Ca2+, Mg2+, K+,Na+) exhibit their highest concentrations between March and June in both PM2.5 and precipitation due mostly to dust. Crustal-derived species concentrations in precipitation exhibit positive relationships with SO42−, NO3−, and Cl−, suggesting that acidic gases likely react with and partition to either crustal particles or hydrometeors enriched with crustal constituents. Concentrations of particulate SO42− show a statistically significant correlation with rain SO42− unlike snow SO42−, which may be related to some combination of the vertical distribution of SO42− (and precursors) and the varying degree to which SO42−-enriched particles act as cloud condensation nuclei versus ice nuclei in the region. The coarse : fine aerosol mass ratio was correlated with crustal species concentrations in snow unlike rain, suggestive of a preferential role of coarse particles (mainly dust) as ice nuclei in the region. Precipitation NO3− : SO42− ratios exhibit the following features with potential explanations discussed: (i) they are higher in precipitation as compared to PM2.5; (ii) they exhibit the opposite annual cycle compared to particulate NO3− : SO42− ratios; and (iii) they are higher in snow relative to rain during the wintertime. Long-term trend analysis for the monsoon season shows that the NO3− : SO42− ratio in rain decreased at the majority of sites due mostly to air pollution regulations of SO42− precursors.

Atmospheric ammonia and particulate inorganic nitrogen over the United States

Article

Full-text available

Aug 2012
ACP

We use in situ observations from the Interagency Monitoring of PROtected Visual Environments (IMPROVE) network, the Midwest Ammonia Monitoring Project, 11 surface site campaigns as well as Infrared Atmospheric Sounding Interferometer (IASI) satellite measurements with the GEOS-Chem model to investigate inorganic aerosol loading and atmospheric ammonia concentrations over the United States. IASI observations suggest that current ammonia emissions are underestimated in California and in the springtime in the Midwest. In California this underestimate likely drives the underestimate in nitrate formation in the GEOS-Chem model. However in the remaining continental United States we find that the nitrate simulation is biased high by a factor of 1.5 or more year-round. None of the uncertainties in precursor emissions, the uptake efficiency of N2O5 on aerosols, OH concentrations, the reaction rate for the formation of nitric acid, or the dry deposition velocity of nitric acid are able to explain this. We find that reducing nitric acid concentrations to 2/3 of their simulated values corrects the bias in nitrate (as well as ammonium) in the US. However the mechanism for this potential reduction is unclear and may be a combination of errors in chemistry, deposition and sub-grid near-surface gradients. This "updated" simulation reproduces PM and ammonia loading and captures the strong seasonal and spatial gradients in gas-particle partitioning across the United States. We estimate that nitrogen makes up 15–35% of inorganic fine PM mass over the US, and that this fraction is likely to increase in the coming decade, both with decreases in sulfur emissions and increases in ammonia emissions.

Chemical characterization and mass closure of PM10 and PM2.5 at an urban site in Karachi – Pakistan

Article

Jan 2016
ATMOS ENVIRON

A mass balance method is applied to assess main source contributions to PM2.5 and PM10 levels in Karachi. Carbonaceous species (elemental carbon, organic carbon, carbonate carbon), soluble ions (Ca++, Mg++, Na+, K+, NH4+, Cl−, NO3−, SO4−), saccharides (levoglucosan, galactosan, mannosan, sucrose, fructose, glucose, arabitol and mannitol) were determined in atmospheric fine (PM2.5) and coarse (PM10) aerosol samples collected under pre-monsoon conditions (March–April 2009) at an urban site in Karachi (Pakistan). The concentrations of PM2.5 and PM10 were found to be 75 μg/m3 and 437 μg/m3 respectively. The large difference between PM10 and PM2.5 originated predominantly from mineral dust. “Calcareous dust” and „siliceous dust” were the over all dominating material in PM, with 46% contribution to PM2.5 and 78% to PM10–2.5. Combustion particles and secondary organics (EC + OM) comprised 23% of PM2.5 and 6% of PM10–2.5. EC, as well as OC ambient levels were higher (59% and 56%) in PM10–2.5 than in PM2.5. Biomass burning contributed about 3% to PM2.5, and had a share of about 13% of “EC + OM” in PM2.5. The impact of bioaerosol (fungal spores) was minor and had a share of 1 and 2% of the OC in the PM2.5 and PM10–2.5 size fractions. In case of secondary inorganic aerosols, ammonium sulphate (NH4)2SO4 contributes 4.4% to PM2.5 and no detectable quantity were found in fraction PM10–2.5. The sea salt contribution is about 2% both to PM2.5 and PM10–2.5.

Comparisons of urban and rural PM10−2.5 and PM2.5 mass concentrations and semi-volatile fractions in Northeastern Colorado

Article

Full-text available

Sep 2015
ACP

Coarse (PM10−2.5) and fine (PM2.5) particulate matter in the atmosphere adversely affect human health and influence climate. While PM2.5 is relatively well studied, less is known about the sources and fate of PM10−2.5. The Colorado Coarse Rural-Urban Sources and Health (CCRUSH) study measured PM10−2.5 and PM2.5 mass concentrations, as well as the fraction of semi-volatile material (SVM) in each size regime (SVM2.5, SVM10−2.5), for three years in Denver and comparatively rural Greeley, Colorado. Agricultural operations east of Greeley appear to have contributed to the peak PM10−2.5 concentrations there, but concentrations were generally lower in Greeley than in Denver. Traffic-influenced sites in Denver had PM10−2.5 concentrations that averaged from 14.6 to 19.7 μg m−3 and mean PM10−2.5/PM10 ratios of 0.56 to 0.70, higher than at residential sites in Denver or Greeley. PM10−2.5 concentrations were more temporally variable than PM2.5 concentrations. Concentrations of the two pollutants were not correlated. Spatial correlations of daily averaged PM10−2.5 concentrations ranged from 0.59 to 0.62 for pairs of sites in Denver and from 0.47 to 0.70 between Denver and Greeley. Compared to PM10−2.5, concentrations of PM2.5 were more correlated across sites within Denver and less correlated between Denver and Greeley. PM10−2.5 concentrations were highest during the summer and early fall, while PM2.5 and SVM2.5 concentrations peaked in winter during periodic multi-day inversions. SVM10−2.5 concentrations were low at all sites. Diurnal peaks in PM10−2.5 and PM2.5 concentrations corresponded to morning and afternoon peaks of traffic activity, and were enhanced by boundary layer dynamics. SVM2.5 concentrations peaked around noon on both weekdays and weekends. PM10−2.5 concentrations at sites located near highways generally increased with wind speeds above about 3 m s−1. Little wind speed dependence was observed for the residential sites in Denver and Greeley.

Interaction of mineral dust with gas phase nitric acid and sulfur dioxide during the MINATROC II field campaign: First estimate of the uptake coefficient ??HNO3 from atmospheric data

Article

Full-text available

Nov 2005

Mineral dust, one of the most abundant aerosols by mass in the atmosphere, may have a lasting but to date almost unexplored effect on the trace gases nitric acid (HNO3) and sulfur dioxide (SO2). These gases have an important influence on, for example, the tropospheric ozone cycle, aerosol formation or acid rain. Within the second part of the MINATROC project (Mineral Dust and Tropospheric Chemistry) we investigated the interaction of mineral dust with gaseous HNO3 and SO2. The measurements were performed on a high mountain plateau (Izaña, Tenerife, 2367 m asl) using the highly sensitive CIMS (Chemical Ionization Mass Spectrometry) technique. During five periods of medium and one period of high atmospheric dust load, the HNO3 concentration decreased with increasing dust concentrations, and in all cases the HNO3 detection limit was reached. From the HNO3 decrease the uptake coefficient gammaHNO3 was calculated for the first time on the basis of in situ measurements. For the observed events, gammaHNO3 varied between 0.017 and 0.054. Moreover, during the dust events a significant decrease of ozone (O3) of the order of 30% was detected. The measurements and the analyses made in this paper show that the direct uptake of O3 on dust is a minor pathway for O3 depletion compared to the indirect effect, i.e., HNO3 depletion on dust which takes away a source of the O3 precursors nitrogen oxides. In contrast, a general interaction between SO2 and mineral dust was not observed. Positive as well as negative and no correlations between SO2 and mineral dust were detected.

Heterogeneous chemistry of individual mineral dust particles with nitric acid: a combined CCSEM/EDX, ESEM, and ICP-MS study

Article

Full-text available

May 2005

The heterogeneous chemistry of individual dust particles from four authentic dust samples with gas phase nitric acid was investigated in this combined computer-controlled scanning electron microscopy with energy-dispersive X-ray (CCSEM/EDX) analysis, environmental scanning electron microscopy (ESEM), and inductively coupled plasma mass spectrometry (ICP-MS) study. Morphology and compositional changes of individual particles as they react with nitric acid were observed using conventional scanning electron microscopy with energy-dispersive X-ray analysis and CCSEM/EDX. ESEM was utilized to investigate the hygroscopic behavior of mineral dust particles reacted with nitric acid. Differences in the reactivity of mineral dust particles from these four different dust source regions with nitric acid were observed. Mineral dust from source regions containing high levels of calcium, namely, China loess dust and Saudi coastal dust, were found to react to the greatest extent. In particular, we show that calcium carbonate rich dust aerosols may exhibit continuous, extensive reactivity with nitric acid resulting in formation of highly hygroscopic calcium nitrate particles. Transformation of dry mineral dust into an aqueous liquid aerosol has a tremendous impact on its light scattering properties, ability to modify clouds, heterogeneous chemistry, and gas to particle partitioning in the atmosphere. ICP-MS was used to estimate maximal extent of possible CaCO3-to-Ca(NO3)2 conversion in the mineral dust samples. We show that in China loess dust and Saudi coastal dust aerosols, formation of calcium nitrate particles can take place at the total extent as high as ~20-40 wt %.

Intercomparison of near real time monitors of PM2.5 nitrate and sulfate at the U.S. Environmental Protection Agency Atlanta Supersite

Article

Full-text available

Jan 2003

Five new instruments for semicontinuous measurements of fine particle (PM2.5) nitrate and sulfate were deployed in the Atlanta Supersite Experiment during an intensive study in August 1999. The instruments measured bulk aerosol chemical composition at rates ranging from every 5 min to once per hour. The techniques included a filter sampling system with automated water extraction and online ion chromatographic (IC) analysis, two systems that directly collected particles into water for IC analysis, and two techniques that converted aerosol nitrate or sulfate either catalytically or by flash vaporization to gaseous products that were measured with gas analyzers. During the one-month study, 15-min integrated nitrate concentrations were low, ranging from about 0.1 to 3.5 mg m À3 with a mean value of 0.5 mg m À3 . Ten-minute integrated sulfate concentrations varied between 0.3 and 40 mg m À3 with a mean of 14 mg m À3 . By the end of the one-month study most instruments were in close agreement, with r-squared values between instrument pairs typically ranging from 0.7 to 0.94. Based on comparison between individual semicontinuous devices and 24-hour integrated filter measurements, most instruments were within 20–30% for nitrate ($0.1– 0.2 mg m À3) and 10–15% for sulfate (1–2 mg m À3). Within 95% confidence intervals, linear regression fits suggest that no biases existed between the semicontinuous techniques and the 24-hour integrated filter measurements of nitrate and sulfate;, however, for nitrate, the semicontinuous intercomparisons showed significantly less variability than intercomparisons amongst the 24-hour integrated filters.

Reactive uptake of HNO3 and H2SO4 in sea-salt (NaCl) particles

Article

Full-text available

Feb 1998
J AEROSOL SCI

Harry ten Brink

Kinetic information on the substitution of sea-salt chloride by nitrate was deduced from a smog chamber investigation on the reaction of airborne NaCl with HNO3. It was found that a measurable reaction only occurred when the NaCl-particles were present in the form of droplets. The substitution of chloride by nitrate was independent of size, which shows that the generation of the product (HCI gas) was the rate-limiting reaction step. The rate of this reaction was more than an order of magnitude slower than the rate at which nitric acid can reach the droplets. The substitution of chloride by sulphate, in a reaction between H2SO4 and NaCl, depended on particle size from which it was concluded that the transport of H2SO4 to the aerosol was the rate-limiting process. The difference in reaction of the two acids is explained by the fact that sulphuric acid is a condensable species, whereas nitric acid is a gas. From the amount of sulphate as a function of size an uptake coefficient for the condensing sulphuric acid was deduced as 0.1 or higher.

Intercomparison and closure calculations using measurements of aerosol species and optical properties during the Yosemite Aerosol Characterization Study

Article

Full-text available

Jul 2005
J GEOPHYS RES

1] Physical and optical properties of inorganic aerosols have been extensively studied, but less is known about carbonaceous aerosols, especially as they relate to the non-urban settings such as our nation's national parks and wilderness areas. Therefore an aerosol characterization study was conceived and implemented at one national park that is highly impacted by carbonaceous aerosols, Yosemite. The primary objective of the study was to characterize the physical, chemical, and optical properties of a carbon-dominated aerosol, including the ratio of total organic matter weight to organic carbon, organic mass scattering efficiencies, and the hygroscopic characteristics of a carbon-laden ambient aerosol, while a secondary objective was to evaluate a variety of semi-continuous monitoring systems. Inorganic ions were characterized using 24-hour samples that were collected using the URG and Interagency Monitoring of Protected Visual Environments (IMPROVE) monitoring systems, the micro-orifice uniform deposit impactor (MOUDI) cascade impactor, as well as the semi-continuous particle-into-liquid sampler (PILS) technology. Likewise, carbonaceous material was collected over 24-hour periods using IMPROVE technology along with the thermal optical reflectance (TOR) analysis, while semi-continuous total carbon concentrations were measured using the Rupprecht and Patashnick (R&P) instrument. Dry aerosol number size distributions were measured using a differential mobility analyzer (DMA) and optical particle counter, scattering coefficients at near-ambient conditions were measured with nephelometers fitted with PM 10 and PM 2.5 inlets, and ''dry'' PM 2.5 scattering was measured after passing ambient air through Perma Pure Nafion 1 dryers. In general, the 24-hour ''bulk'' measurements of various aerosol species compared more favorably with each other than with the semi-continuous data. Semi-continuous sulfate measurements correlated well with the 24-hour measurements, but were biased low by about 0.15 mg/m 3 . Semi-continuous carbon concentrations did not compare favorably with 24-hour measurements. Fine mass closure calculations suggested that the factor for estimating organic mass from measurements of carbon was approximately 1.8. Furthermore, fine scattering closure calculations showed that the use of 4.0 m 2 /g for the fine organic mass scattering coefficient was an underestimate by at least 30% for periods with high organic mass concentrations.

Direct observations of the atmospheric processing of Asian mineral dust

Article

Full-text available

May 2006

The accumulation of secondary acid products and ammonium on individual mineral dust particles during ACE-Asia has been measured in real-time using ATOFMS. Changes in the amounts of sulphate, nitrate, and chloride mixed with dust particles corresponded to different air mass source regions. During volcanically influenced periods, dust mixed with sulphate dominated. This rapidly switched to dust predominantly mixed with chloride when the first Asian dust front reached the R/V Ronald Brown. We hypothesise that the high degree of mixing of dust with chloride was caused by the prior reaction of NOy(g) and volcanic SO2(g) with sea salt particles, reducing the availability of nitrate and sulphate precursors while releasing HCl(g), which then reacted with the incoming dust front. The segregation of sulphate from nitrate and chloride in individual dust particles is demonstrated for the first time. This is likely caused by the dust plume encountering elevated SO2(g) in the Chinese interior before reaching coastal urban areas polluted by both SO2(g) and NOx(g). This caused the fractions of dust mixed with nitrate and/or chloride to be strongly dependent on the total dust loadings, whereas dust mixed with sulphate did not show this same dust concentration dependence. Ammonium was also significantly mixed with dust and the amount correlated strongly with the total amount of secondary acid reaction products in the dust. Submicron dust and ammonium sulphate were internally mixed, contrary to frequent statements that they exist as an external mixture. The size distribution of the mixing state of dust with these secondary species validates previous models and mechanisms of the atmospheric processing of dust. The uptake of secondary acids was also dependent on the individual dust particle mineralogy; nitrate accumulated on calcium-rich dust while sulphate accumulated on aluminosilicate-rich dust. Oxidation of S(IV) to S(VI) by iron in the aluminosilicate-rich dust is a probable explanation for this result, with important consequences for dust as a vector for the fertilization of remote oceans by soluble iron. This series of novel results has important implications for improving the treatment of dust in global chemistry models and highlights several key processes requiring further investigation through laboratory and field studies.

Exposures to Acidic Aerosols

Article

Full-text available

Mar 1989

Ambient monitoring of acid aerosols in four U.S. cities and in a rural region of southern Ontario clearly show distinct periods of strong acidity. Measurements made in Kingston, TN, and Steubenville, OH, resulted in 24-hr H+ ion concentrations exceeding 100 nmole/m3 more than 10 times during summer months. Periods of elevated acidic aerosols occur less frequently in winter months. The H+ determined during episodic conditions in southern Ontario indicates that respiratory tract deposition can exceed the effects level reported in clinical studies. Observed 12-hr H+ concentrations exceeded 550 nmole/m3 (approximately 27 micrograms/m3 H2SO4). The maximum estimated 1-hr concentration exceeded 1500 nmole/m3 for H+ ions. At these concentrations, an active child might receive more than 2000 nmole of H+ ion in 12 hr and in excess of 900 nmole during the hour when H2SO4 exceeded 50 micrograms/m3.

Direct Observation of Heterogeneous Chemistry in the Atmosphere

Article

Full-text available

Mar 1998
SCIENCE

The heterogeneous replacement of chloride by nitrate in individual sea-salt particles was monitored continuously over time in the troposphere with the use of aerosol time-of-flight mass spectrometry. Modeling calculations show that the observed chloride displacement process is consistent with a heterogeneous chemical reaction between sea-salt particles and gas-phase nitric acid, leading to sodium nitrate production in the particle phase accompanied by liberation of gaseous HCl from the particles. Such single-particle measurements, combined with a single-particle model, make it possible to monitor and explain heterogeneous gas/particle chemistry as it occurs in the atmosphere.

Aerosol Ion Characteristics During the Big Bend Regional Aerosol and Visibility Observational Study

Article

Full-text available

Jun 2004

The ionic compositions of particulate matter with aerodynamic diameter < or = 2.5 microm (PM2.5) and size-resolved aerosol particles were measured in Big Bend National Park, Texas, during the 1999 Big Bend Regional Aerosol and Visibility Observational study. The ionic composition of PM2.5 aerosol was dominated by sulfate (SO4(2-)) and ammonium (NH4+). Daily average SO4(2-) and NH4+ concentrations were strongly correlated (R2 = 0.94). The molar ratio of NH4+ to SO4(2-) averaged 1.54, consistent with concurrent measurements of aerosol acidity. The aerosol was observed to be comprised of a submicron fine mode consisting primarily of ammoniated SO4(2-) and a coarse particle mode containing nitrate (NO3-). The NO3- appears to be primarily associated with sea salt particles where chloride has been replaced by NO3-, although formation of calcium nitrate (Ca(NO3)2) is important, too, on several days. Size-resolved aerosol composition results reveal that a size cut in particulate matter with aerodynamic diameter < or = 1 microm would have provided a much better separation of fine and coarse aerosol modes than the standard PM2.5 size cut utilized for the study. Although considerable nitric acid exists in the gas phase at Big Bend, the aerosol is sufficiently acidic and temperatures sufficiently high that even significant future reductions in PM2.5 SO4(2-) are unlikely to be offset by formation of particulate ammonium nitrate in summer or fall.

Particulate Nitrate Measurement Using Nylon Filters

Article

Full-text available

Sep 2005

Nylon filters are a popular medium to collect atmospheric fine particles in different aerosol monitoring networks, including those operated by the U.S. Environmental Protection Agency and the Interagency Monitoring of Protected Visual Environments (IMPROVE) program. Extraction of the filters by deionized water or by a basic aqueous solution (typically a mixture of sodium carbonate and sodium bicarbonate) is often performed to permit measurement of the inorganic ion content of the collected particles. Whereas previous studies have demonstrated the importance of using a basic solution to efficiently extract gaseous nitric acid collected using nylon filters, there has been a recent movement to the use of deionized water for extraction of particles collected on nylon filters to eliminate interference from sodium ion (Na+) during ion chromatographic analysis of inorganic aerosol cations. Results are reported here from a study designed to investigate the efficiency of deionized water extraction of aerosol nitrate (NO3-) and sulfate from nylon filters. Data were obtained through the conduct of five field experiments at selected IMPROVE sites. Results indicate that the nylon filters provide superior retention of collected fine particle NO3-, relative to Teflon filters, and that deionized water extraction (with ultrasonication) of collected NO3- and sulfate is as efficient, for the situations studied, as extraction using a basic solution of 1.7 mM sodium bicarbonate and 1.8 mM sodium carbonate.

Aerosol Ion Characteristics during the Big Bend Regional Aerosol and Visibility Observational Study

Article

May 2004

The ionic compositions of particulate matter with aerodynamic diameter ≤2.5 μm (PM2.5) and size-resolved aerosol particles were measured in Big Bend National Park, Texas, during the 1999 Big Bend Regional Aerosol and Visibility Observational study. The ionic composition of PM 2.5 aerosol was dominated by sulfate (SO42-) and ammonium (NH4+). Daily average SO42- and NH4+ concentrations were strongly correlated (R2 = 0.94). The molar ratio of NH4+ to SO42- averaged 1.54, consistent with concurrent measurements of aerosol acidity. The aerosol was observed to be comprised of a submicron fine mode consisting primarily of ammoniated SO 42- and a coarse particle mode containing nitrate (NO 3-). The NO3- appears to be primarily associated with sea salt particles where chloride has been replaced by NO3-, although formation of calcium nitrate (Ca(NO 3)2) is important, too, on several days. Size-resolved aerosol composition results reveal that a size cut in particulate matter with aerodynamic diameter ≤1 μm would have provided a much better separation of fine and coarse aerosol modes than the standard PM2.5 size cut utilized for the study. Although considerable nitric acid exists in the gas phase at Big Bend, the aerosol is sufficiently acidic and temperatures sufficiently high that even significant future reductions in PM2.5 SO42- are unlikely to be offset by formation of particulate ammonium nitrate in summer or fall.

Direct Observation of Heterogeneous Chemistry in the Atmosphere

Article

Feb 1998

Eric E Gard

Heterogeneous Interactions of HOBr, HNO3, O3, and NO2with Deliquescent NaCl Aerosols at Room Temperature

Article

May 1998

To better quantify the rates at which key trace gases interact with sea-salt aerosols, the kinetics of uptake of HOBr, HNO3, O3, and NO2 by deliquescent NaCl aerosols at 75% relative humidity (RH) and room temperature have been studied using an aerosol kinetics flow tube technique. Results for HOBr indicate that the uptake coefficient (γ) is larger than 0.2 for highly acidic aerosols at pH 0.3 and for aerosols that have been buffered to pH 7.2 using a 0.25 M NaH2PO4/Na2HPO4 buffer. For unbuffered NaCl aerosols, the HOBr uptake coefficient due to reaction is less than 1.5 × 10-3. For HNO3, the uptake coefficient on unbuffered, NaCl aerosols is greater than 0.2, being driven by the very high solubility of HNO3 in aqueous salt solutions. Both NO2 and O3 show low reactivity on pH neutral aerosols with upper limits to the uptake coefficients of 10-4. With acidic aerosols, slight O3 loss occurs either on the walls of the flow tube or on the aerosols, giving rise to Cl2. These experiments are the first reported kinetics studies of the loss of HOBr, HNO3, and O3 on aqueous NaCl solutions, and they imply that gas-phase diffusion, and not reaction kinetics, determines the mass-transfer rates of gas-phase HNO3 and HOBr to marine aerosols in the boundary layer. Also, the HOBr results support modeling studies which have proposed that HOBr uptake initiates autocatalytic release of bromide from sea-salt aerosols.

Measurement and evaluation of acid air pollutants in Chicago using an annular denuder system

Article

Mar 1993
Atmos Environ Gen Top

The cyclone/annular denuder/filter pack sampling system (ADS) was used to collect and evaluate ambient air pollutants in Chicago. Eighty-one 12-h samples, equally divided into day/night intervals, were collected from April 1990 to March 1991. The chemical species measured were HNO3, HNO2, SO2 and NH3 in the gas phase, and SO42−, NO3−, NH4+, and H+ in the particulate phase.The ADS data were collected simultaneously with PM10 samples. The particulate matter was analysed for elemental composition. These compositions were combined with the ADS observations and subjected to evaluation using a chemical mass balance receptor model (CMB). From the CMB analysis, the sum of the contributions from soil (15%), mobile (14%), incinerator (2%), coal (0.6%), steel (0.3%) and refinery (0.2%) was 32% of the PM10. NO3−, which was not included in the fingerprints, represented an additional 9% of the PM10. Residual SO42− and residual organic carbon, possibly formed in the atmosphere, represented an additional 22 and 20% of the PM10, respectively, leaving only 17% from other unidentified sources. From the standpoint of source contributions of sulfur and nitrogen compounds, coal combustion (23%) and refinery emissions (23%) are the major contributors of ambient sulfur (with 49% from unidentified sources). Mobile sources (87%) contributed most of the ambient nitrogen (with only 2% from unidentified sources).

Characterization and formation of particulate nitrate in a coastal area

Article

Melissa Cheryl Foster Evans

Particulate nitrates play important roles in the atmosphere. They consist mainly of NH4NO3 and NaNO3, products from the reactions of gaseous HNO3 with gaseous NH3 and sea salt, respectively. The gas-to-particle phase conversion of nitrate changes its deposition characteristics and ultimately changes the transport and deposition rates of the locally produced species. Studies were conducted to develop background information on the particle concentrations and size distributions and the chemistry and kinetics behind the interactions. The predominant nitrate species in the Tampa Bay area was identified as coarse mode NaNO3. NH4NO3 was not detected as it has high volatility at ambient temperatures. Spatial distribution sampling determined a gradient of NaCl and NaNO3 with increased distance from the coastal shore and an increase in the gas-to-particle conversion of nitric acid along a predominant air mass trajectory. The EQUISOLV II thermodynamic equilibrium model was evaluated. It was determined that the model can be used to predict gas and size-distributed particulate matter concentrations. The model was also used to examine the gas-to-particle partitioning of nitric acid to nitrate by NaCl and CaCO3. Both sodium and calcium partitioned nitrate to the particle phase. The magnitude of the partitioning was directly dependent on the equilibrium coefficients. The fine mode percentage of the total nitrate was determined using two methods. The results were used to expand the current data set to account for the coarse mode nitrate, and they indicated that particle nitrate accounted for 9% of the total nitrogen deposition flux to Tampa Bay. The formation of particle nitrate was examined using a nitrate accumulation model. Results indicated that the equilibrium time for particles less than 10 um in diameter was significantly less than their atmospheric residence time, with fastest conversion occurring under the highest relative humidity conditions. This information is vital in the development of atmospheric nitrogen dry deposition estimates, which are used to assess water quality and nutrient loading. These data can be used to determine air-monitoring strategies and to develop models that account for the coarse particle nitrogen species.

A laboratory study of the heterogeneous reaction of nitric acid on calcium carbonate particles

Article

Dec 2000

It has been postulated that the reaction of nitric acid with calcium carbonate, namely, CaCO3(s)+2HNO3(g)->Ca(NO3)2(s)+CO2(g)+H2O(g), plays an important role in the atmosphere. In this study, transmission FTIR spectroscopy, diffuse reflectance UV-visible spectroscopy, transmission electron microscopy and a Knudsen cell reactor coupled to a quadrupole mass spectrometer have been used to investigate the heterogeneous reactivity of HNO3 on CaCO3 at 295 K as a function of relative humidity. Transmission FTIR spectroscopy was used to probe both gas-phase and adsorbed products and showed that the reaction of HNO3 and CaCO3 is limited to the surface of the CaCO3 particle in the absence of adsorbed water. However, in the presence of water vapor, the reaction is greatly enhanced and is not limited to the surface of the particle producing both solid calcium nitrate and gaseous carbon dioxide. The enhanced reactivity of the particles is attributed to the presence of a layer of adsorbed water on the particle surface. The amount of adsorbed water on the particle surface is strongly dependent on the extent of the reaction. This can be understood in terms of the increased hydrophilicity of calcium nitrate as compared to calcium carbonate. Data from experiments using a mass-calibrated Knudsen cell reactor showed the stoichiometry for the reaction determined from gas-phase species deviated from that expected from the balanced equation. Water adsorption on the particle surface and gases dissolved into the water layer appear to be the cause of this discrepancy. The measured uptake coefficient accounting for the BET area of the sample is determined to be 2.5+/-0.1×10-4 for HNO3 on CaCO3 under dry conditions and is found to increase in the presence of water vapor. Atmospheric implications of the results presented here are discussed.

Heterogeneous reactions of NO2 and HNO3 on oxides and mineral dust: A combined laboratory and modeling study

Article

Aug 2001

This study combines laboratory measurements and modeling analysis to quantify the role of heterogeneous reactions of gaseous nitrogen dioxide and nitric acid on mineral oxide and mineral dust particles in tropospheric ozone formation. At least two types of heterogeneous reactions occur on the surface of these particles. Upon initial exposure of the oxide to NO2 there is a loss of NO2 from the gas phase by adsorption on the particle surface, i.e., NO2(g)->NO2(a). As the reaction proceeds, a reduction of gaseous NO2 to NO, NO2(g)->NO(g) is found to occur. Initial uptake coefficients gamma0 for NO2 on the surface of these particles have been measured at 298 K using a Knudsen cell reactor coupled to a mass spectrometer. For the oxides studied, alpha,gamma-Al2O3, alpha,gamma-Fe2O3, TiO2, SiO2, CaO, and MgO, gamma0 ranges from

Modeling and Characterization of a Particle-into-Liquid Sampler (PILS)

Article

Jul 2006

A modified particle-into-liquid sampler (PILS), based on the original design of Weber et al. (2001), is presented. The principal modification in this design is that collected liquid sample is delivered to vials held on a rotating carousel as opposed to an on-line analytical detector. A model is developed to predict aerosol mass concentrations measured by a PILS based on operating parameters and characteristics of the sampled aerosol. A backward model predicts the concentrations of the sampled aerosol based on operating parameters and concentrations measured by the PILS. Both models, which consider plumbing transmission efficiencies, droplet growth, mixing effects, and volatilization losses, predict mass concentrations that are consistent with laboratory tests for step changes in concentration. The average collection efficiency for species (Na^+, K^+, SO_4^(2−), Cl^−, NO_3^−) from a variety of aerosols compared to simultaneous measurements with a differential mobility analyzer (DMA) exceeded 96% except for NH_4^+ (88%); NH_4^+ is theoretically shown to be the most vulnerable to volatilization, followed by Cl^- and then NO_3^− , with greater losses caused by increasing droplet pH and temperature. The characterization tests highlight the importance of reducing NH_4^+ volatilization by keeping a stable tip temperature of 100°C at the point where steam and ambient air mix in the condensation chamber. Maintaining a stable tip temperature also avoids fluctuations in supersaturations that lead to increased deposition losses of larger droplets. Sample data from the 2004 International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) field campaign are presented.

Heterogeneous Reactivity of Gaseous Nitric Acid on Al 2 O 3 , CaCO 3 , and Atmospheric Dust Samples: A Knudsen Cell Study

Article

Apr 2001

The heterogeneous reaction between HNO3 and various authentic and synthetic mineral dust/mineral oxide surfaces has been investigated using a low-pressure Knudsen reactor operating at 298 K. The surfaces used were Saharan dust from Cape Verde, Arizona dust, CaCO3, and Al2O3 In ail cases, a large irreversible uptake was observed. An uptake coefficient of gamma = (II +/- 3) x 10(-2) was determined for Saharan dust, and gamma = (6 +/- 1.5) x 10(-2) was obtained for Arizona dust. The uptake coefficients for HNO3 on heated CaCO3 and on unheated CaCO3 are given by gamma = (10 +/- 2.5) x 10(-2) and (18 +/- 4.5) x 10(-2), respectively, and are in good agreement with previous results. CO2 and H2O were formed as gas-phase products. Measurements of the uptake coefficient of HNO3 on grain-size selected samples of Al2O3, gamma = (13 +/- 3.3) x 10(-2), and systematic variation of sample mass enabled us to show that the geometrical surface area of the dust sample is appropriate for calculation of uptake coefficients in these experiments. The high reactivity of HNO3 toward dust samples highlights the potentially important role of mineral dust in redistributing nitrate from the gaseous to the particulate phase and modifying tropospheric photochemical oxidation cycles.

Chemical interaction between mineral dust particles and acid gases during Asian dust events

Article

Feb 2005

Acid gas reactions during the passage from the source regions to the western North Pacific modify the chemical characteristics of Asian mineral dust particles as they pass through heavily industrial regions. We conducted aerosol samplings to investigate the interaction of mineral dust particles with acid gases in the western North Pacific region during the high-dust season. The concentration peaks of NO3- and mineral dust particles were in the coarse mode range (D > 1.25 mum) in all aerosol samples, while non-sea-salt-(nss)-SO42- had an apparent peak in the coarse mode range only in an Asian dust event that experienced rain. Nitrate was the dominant acid substance associated with the mineral dust particles rather than nss-SO42-. In the urban air of Tokyo we also conducted an in situ experiment to react ambient acid gases with mineral dust particle loaded on a filter. The in situ experiment indicated that HNO3 had reacted with mineral dust particles much more efficiently than SO2 had. HNO3 (+NO2) and HCl accounted for large fractions (48% and 40%) of acid gases that reacted with mineral dust particles, while SO2 accounted for a small fraction (12%). The high adsorption of HNO3 on mineral dust particles would change their surface properties from hydrophobic to hygroscopic and form an efficient mechanism to remove nitrogen compounds to the ocean surface layer.

A Particle-into-Liquid Collector for Rapid Measurement of Aerosol Bulk Chemical Composition

Article

Sep 2001

We report on a new instrument developed for rapid automated on-line and continuous measurement of ambient aerosol bulk com- position.Thegeneralapproachisbasedonearlierdevices(Khlystov et al. 1995; Simon and Dasgupta 1995) in which ambient particles are mixed with saturated water vapor to produce droplets easily collected by inertial techniques. The resulting liquid stream is an- alyzed with an ion chromatograph to quantitatively measure the bulk aerosol ionic components. In this instrument, a modié ed ver- sion of a particle size magnié er (Okuyama et al. 1984) is employed to activate and grow particles comprising the é ne aerosol mass. A single jet inertialimpactor isused tocollect the droplets onto a ver- tical glass plate that is continually washed with a constant water diluent è ow of nominally 0.10 ml min¡ 1. The è ow is divided and then analyzed by a dual channel ion chromatograph. In its current form, 4.3 min integrated samples were measured every 7 min. The instrument provides bulk composition measurements with a detec- tion limit of approximately 0.1 πg m¡ 3 for chloride, nitrate, sul-

Knudsen Cell Studies of the Reaction of Gaseous Nitric Acid with Synthetic Sea Salt at 298 K

Article

Dec 1997

The uptake of nitric acid on synthetic sea salt (SSS) was studied at 298 K using a Knudsen cell with mass spectrometric detection of the gaseous reactant and products. HCl was the only product observed, with yields of 100% within experimental error. Nitric acid reaction probabilities decreased with reaction time by a factor of 2−3, ultimately reaching a constant value. Both the higher initial reaction probabilities (which ranged from 0.07 to 0.75) and the final steady-state values (which ranged from 0.03 to 0.25) decreased if the salt had been heated at 75 °C while pumping to decrease the amount of water on the salt surface prior to reaction. Several experiments using MgCl2·6H2O also gave very large nitric acid reaction probabilities, ≥0.14 in all cases, consistent with the important role of crystalline hydrates in the reactivity of SSS observed in earlier studies. The presence of large amounts of water on the SSS surface was illustrated by two phenomena: (1) the uptake of D2O and liberation of large amounts of HDO and smaller amounts of H2O and (2) the formation of gaseous HCl, rather than DCl, as the major product of the DNO3 reaction with SSS. The results of these experiments confirm the critical role of surface-adsorbed water in the uptake and reaction of HNO3 with salt surfaces, as proposed earlier based on similar studies of the reaction of HNO3 with NaCl. They also suggest that the reaction probability for HNO3 with sea salt particles below the deliquescence point is approximately an order of magnitude larger than for reaction with pure NaCl, the major component of these particles. The atmospheric implications are discussed.

Chemical Reactions of Nitrogen Oxides on the Surface of Oxide, Carbonate, Soot, and Mineral Dust Particles: Implications for the Chemical Balance of the Troposphere

Article

Jan 2002

Vicki H. Grassian

Particles present in the Earth's atmosphere provide reactive surfaces for potentially important chemistry. The role of heterogeneous reactions of trace atmospheric gases on solid aerosol surfaces present in the troposphere is not well understood. Laboratory investigations can provide a basis for understanding the detailed molecular- level physical chemistry of these atmospheric reactions. Kinetic data measured in the laboratory, along with the information provided by spectroscopic studies, can be incorporated into atmospheric chemistry models in order to gain a greater understanding of how heterogeneous chemistry affects the chemical balance of the troposphere. Laboratory studies of the heterogeneous uptake of nitric acid, HNO3, on oxide, carbonate and mineral dust particles, and the heterogeneous formation of nitrous acid, HONO, on wetted-SiO2 and soot particles are highlighted as two examples of important heterogeneous processes in the troposphere.

Distribution of nitrate over sea-salt and soil derived particles — Implications from a field study

Article

Jun 1996

A method for determining the distribution of supermicrometer nitrate between size-segregated sea-salt and soil derived particles is presented. The analysis is based on field data from six measurements at a coastal site in southern Finland, and on a theoretical treatment taking into account the transfer of gaseous species onto particle surfaces and their subsequent reaction. Significant amounts of nitrate were found in both the particle types, with the fraction of nitrate associated with soil particles varying from 20–50% in the 1–2 m size to near 90% in particles larger than 10 m. Overall, the nitrate accumulation followed closely the relative abundances of these two particle types. Two overlapping modes in supermicron nitrate mass size distributions could be identified. The lower mode, associated with sea-salt, was located between the surface-area and volume distribution of sodium peaking at about 2–3 m of EAD. The upper mode peaked at 3–5 m and followed more closely the surface-area distribution of calcium in all samples. At our site, the accumulation of nitrate into both particle types was shown to be limited by an effective surface reaction rate rather than by gas-phase diffusion. This rate was estimated to be considerably larger for sea-salt particles. Strong evidence in support of the saturation of nitrate in sea-salt particles were obtained.

Loss of fine particle ammonium from denuded nylon filters

Article

Aug 2006
Atmos Environ

Ammonium is an important constituent of fine particulate mass in the atmosphere, but can be difficult to quantify due to possible sampling artifacts. Losses of semivolatile species such as NH4NO3 can be particularly problematic. In order to evaluate ammonium losses from aerosol particles collected on filters, a series of field experiments was conducted using denuded nylon and Teflon filters at Bondville, IL (February 2003), San Gorgonio, CA (April 2003 and July 2004), Grand Canyon NP, AZ (May, 2003), Brigantine, NJ (November 2003), and Great Smoky Mountains National Park (NP), TN (July–August 2004). Samples were collected over 24 h periods. Losses from denuded nylon filters ranged from 10% (monthly average) in Bondville, IL to 28% in San Gorgonio, CA in summer. Losses on individual sample days ranged from 1% to 65%. Losses tended to increase with increasing diurnal temperature and relative humidity changes and with the fraction of ambient total N(−III) (particulate NH4++gaseous NH3) present as gaseous NH3. The amount of ammonium lost at most sites could be explained by the amount of NH4NO3 present in the sampled aerosol. Ammonium losses at Great Smoky Mountains NP, however, significantly exceeded the amount of NH4NO3 collected. Ammoniated organic salts are suggested as additional important contributors to observed ammonium loss at this location.

An improved method for measuring aerosol strong acidity: Results from a nine-month study in St Louis, Missouri and Kingston, Tennessee

Article

Dec 1988
Atmos Environ

An improved method for measuring strong acidity of atmospheric aerosols is presented. An ammonia diffusion dénuder was developed to prevent neutralization of the acidic aerosol samples. In addition, a new procedure for protecting samples during shipment and analysis was used. An increase in the sensitivity of the analysis was achieved by extraction of the aerosol sample in a small solution volume, 3 ml, of 10−4 N HClO4, and the use of a microelectrode for pH determination. Finally, results from a nine-month study in St Louis, Missouri and Kingston, Tennessee are given.

Refinements to the Particle-Into-Liquid Sampler (PILS) for Ground and Airborne Measurements of Water Soluble Aerosol Composition

Article

Mar 2003
ATMOS ENVIRON

An improved particle-into-liquid sampler (PILS) has proven successful in both ground-based and aircraft experiments for rapid measurements of soluble aerosol chemical composition. Major modifications made to the prototype PILS (Aerosol Sci. Technol. 35 (2001) 718) improve particle collection at higher sample flow (15–17 l min−1) while maintaining minimal sample dilution. Laboratory experiments using a fluorescent calibration aerosol aided in designing the present system and characterized the PILS collection efficiency as a function of particle size. Collection efficiency for particle diameters Dp between 0.03 and 10 μm is greater than 97%. In addition, the instrument now samples at low pressures (0.3 atmosphere) necessary for airborne measurements up to approximately 8 km in altitude. An ion chromatograph (IC) is coupled to the PILS for direct on-line analysis of the collected sample (hence the name ‘PILS-IC’). Proper selection of columns and eluants allows for 3.5–4 min separation of 9 major inorganic species (Na+, NH4+, K+, Ca2+, Mg2+, Cl−, NO3−, NO2−, SO42−), while acetate, formate, and oxalate, are also possible in 15 min. Any analytical technique capable of continuous online analysis of a liquid sample can be coupled to the PILS for quantitative semi-continuous measurements of aerosol composition. Changes made to the prototype are explained and data from a recent experiment are compared with standard integrated filter measurements.

Formation of nitrate and non-sea-salt sulfate on coarse particles - The role of aerosol water content and size distribution

Article

Nov 1999
ATMOS ENVIRON

The formation of nitrate and sulfate on coarse particles and its relationships with meteorological conditions and relative abundance of sea-salt and soil particles were studied. Size distributions of particulate , Cl−, Na+, K+, Mg2+ and Ca2+ were measured using a MOUDI cascade impactor for 11 days in July to December 1997 at a coastal site in Hong Kong. Most of the nitrate and a small fraction of sulfate were distributed in the coarse mode. Since Hong Kong is influenced by both marine and continental aerosols, the distribution of coarse mode nitrate and sulfate depends on the weather conditions. Evidence of nitrate formation on both sea-salt and soil compounds was found in this study. Chloride depletion of sea-salt by both nitrate and sulfate formation was also observed. When Hong Kong was under prevailing easterly wind accompanied with high relative humidity, Na+ was the dominant cation species and significant chloride depletion (74–88%) from coarse mode sea-salt aerosols was observed. Nitrate accounted for 65% of chloride depletion. During a heavily polluted period when there were high concentrations of both fine (18 μg m−3) and coarse mode (3 μg m−3) sulfate, significant amount of sulfate was associated with sea-salt particles and accounted for 11–29% of the chloride depletion. At least 16% of chloride depletion was not accounted for by nitrate and sulfate alone in this episode. When Hong Kong was influenced by a northeasterly monsoon, Ca2+ was the dominant species in the coarse mode. Soil particles compete with sea-salt particles for acidic gases. Chloride depletion was below 50% and most of the nitrate was found to be associated with Ca2+ in soil particles.

Effect of sea salt and calcium carbonate interactions with nitric acid on the direct dry deposition of nitrogen to Tampa Bay, Florida

Article

Sep 2004
ATMOS ENVIRON

Equilibrium modeling predicts that atmospheric sea salt and CaCO3 can partition gas-phase HNO3 to solid or aqueous-phase NaNO3 and Ca(NO3)2. We hypothesized that this partitioning reduces the direct dry deposition of nitrogen to Tampa Bay, as the average deposition velocities of the aerosol species are typically less than that of the gas. As a corollary to this, we investigated whether a 15-μm diameter particle could remain suspended in the atmosphere long enough for the gas-to-particle nitrogen transfer to represent a significant fraction of the nitrogen flux. To test these hypotheses, we applied to local inorganic aerosol concentration and size distribution measurements a published nitrate accumulation model with literature values of uptake coefficients. For the time-dependent NaNO3 and Ca(NO3)2 formation computations, we adopted a closed-system approach and assumed externally mixed particles, and considered relative humidity averages of 60%, 78% and 90%. An integrated NOAA Buoy gas deposition and Williams particle deposition model was used with 1 year of local meteorology and water temperature data to obtain average over water deposition velocities, segregated by the 25th, 50th and 75th percentile wind speeds. The calculated HNO3 dry deposition rates in the absence of aerosols were 0.61, 1.5 and 3.3 kg-N ha−1 yr−1 at the low, medium and high wind speeds, respectively. Modeled reductions in the dry nitrogen flux ranged from 15% at low wind speed and high relative humidity conditions to 76% at high wind speed and high relative humidity conditions. The modeled flux divergence indicated that sea salt and mineral dust diminished the direct HNO3 nitrogen deposition to Tampa Bay. Modeled nitrate nitrogen deposition rates, however, were dominated by nitrogen transferred to a 15-μm diameter particle. These results highlight the need to both monitor and model the coarse particle nitrogen for estimating nitrogen deposition in a coastal environment.

Atmospheric Chemistry and Physics: From Air Pollution to Climate Change

Chapter

Oct 1998

Scitation is the online home of leading journals and conference proceedings from AIP Publishing and AIP Member Societies

Heterogeneous Reactivity of Gaseous Nitric Acid on Al2O3, CaCO3, and Atmospheric Dust Samples: A Knudsen Cell Study

Article

Apr 2001

The heterogeneous reaction between HNO3 and various authentic and synthetic mineral dust/mineral oxide surfaces has been investigated using a low-pressure Knudsen reactor operating at 298 K. The surfaces used were Saharan dust from Cape Verde, Arizona dust, CaCO3, and Al2O3. In all cases, a large irreversible uptake was observed. An uptake coefficient of γ = (11 ± 3) × 10-2 was determined for Saharan dust, and γ = (6 ± 1.5) × 10-2 was obtained for Arizona dust. The uptake coefficients for HNO3 on heated CaCO3 and on unheated CaCO3 are given by γ = (10 ± 2.5) × 10-2 and (18 ± 4.5) × 10-2, respectively, and are in good agreement with previous results. CO2 and H2O were formed as gas-phase products. Measurements of the uptake coefficient of HNO3 on grain-size selected samples of Al2O3, γ = (13 ± 3.3) × 10-2, and systematic variation of sample mass enabled us to show that the geometrical surface area of the dust sample is appropriate for calculation of uptake coefficients in these experiments. The high reactivity of HNO3 toward dust samples highlights the potentially important role of mineral dust in redistributing nitrate from the gaseous to the particulate phase and modifying tropospheric photochemical oxidation cycles.

Uptake of Nitrate and Sulfate on Dust Aerosols during TRACE-P

Article

Oct 2003

Aerosol data collected near Asia on the DC-8 aircraft platform during TRACE-P has been examined for evidence of uptake of NO3(-) and SO4(-) on dust surfaces. Data is compared between a sector where dust was predominant and a sector where dust was less of an influence. Coincident with dust were higher mixing ratios of anthropogenic pollutants. HNO3, SO2, and CO were higher in the dust sector than the nondust sector by factors of 2.7, 6.2, and 1.5, respectively. The colocation of dust and pollution sources allowed for the uptake of NO3(-) and nss-SO4(-) on the coarse dust aerosols, increasing the mixing ratios of these particulates by factors of 5.7 and 2.6 on average. There was sufficient nss-SO4(-) to take up all of the NH4(+) present, with enough excess nss-SO4(-) to also react with dust CaCO3. This suggests that the enhanced NO3(-) was not in fine mode NH4NO3. Particulate NO3(-) (p-NO3(-)) constituted 54% of the total NO3(-), (t-NO3(-)) on average, reaching a maximum of 72% in the dust sector. In the nondust sector, p-NO3(-) contributed 37% to t-NO3(-), likely due to the abundance of sea salts there. In two other sectors where the influence of dust and sea salt were minimal, p-NO3(-), accounted for < 15% of t-NO3(-).

Indoor and Outdoor Concentrations of Inorganic Acidic Aerosols and Gases

Article

Mar 1991
J AIR WASTE MANAGE

Annular denuder-filter pack sampling systems were used to make indoor and outdoor measurements of aerosol strong H+, SO4(2-), NH4+, NO3- and NO2-, and the gaseous pollutants SO2, HNO3, HONO and NH3 during summer and winter periods in Boston, Massachusetts. Outdoor levels of SO2, HNO3, H+ and SO4(2-) exceeded their indoor concentrations during both seasons. Winter indoor/outdoor ratios were lower than during the summer, probably due to lower air exchange rates during the winter period. During both monitoring periods, indoor/outdoor ratios of aerosol strong H+ were 40-50 percent of the indoor/outdoor SO4(2-) ratio. Since aerosol strong acidity is typically associated with SO4(2-), this finding is indicative of neutralization of the acidic aerosol by the higher indoor NH3 levels. Geometric mean indoor/outdoor NH3 ratios of 3.5 and 23 respectively were measured for the summer and winter sampling periods. For HONO, NH3, NH4+ and NO2-, indoor concentrations were significantly higher than ambient levels. Indoor levels of NO3- were slightly less than outdoor concentrations.

Quantitative Time-Resolved Monitoring of Nitrate Formation in Sea Salt Particles Using a CCSEM/EDX Single Particle Analysis

Article

Jan 2003

Progress of the nitrate formation in individual sea salt particles was detected as a function of time using aerosol samples collected during the TexAQS 2080 experiment We demonstrate that the time-resolved collection approach coupled with the automated EDX single particle analysis made it possible to follow in detail the time evolution of sea salt particles within a diverse aerosol mixture. Using a custom built Time-Resolved Aerosol Collector (TRAC), particulate samples were taken sequentially on grid-supported 50 nm carbon films with a time resolution of 10 min between two consecutive samples. The samples were analyzed in the laboratory using Computer Controlled Scanning Electron Microscopy with Energy-Dispersed analysis of X-rays (CCSEM/EDX). Between midnight of 08/16/00 and the early morning of 08/17/00, a steady, particularly sea salt rich aerosol was observed at the measurement site, which later showed the effects of atmospheric processing. During the night of 08/17/00 the sea salt particles were almost unprocessed, having elemental composition close to that of seawater. By 12 noon, the evolving atmosphere was able to completely convert them, predominantly to sodium nitrate particles. During the next night this process had nearly stopped and fairly virgin sea salt particles appeared again.

Heterogeneous chemistry of individual mineral dust particles with nitric acid: A combined Measurement and evaluation of acid air pollutants in Chicago using an annular denuder system

Jan 1993
543-553

A Laskin
T W Wietsma
B J Krueger
V H Grassian
Ccsem
Edx
Icp-Ms Esem

Laskin, A., Wietsma, T.W., Krueger, B.J., Grassian, V.H., 2005. Heterogeneous chemistry of individual mineral dust particles with nitric acid: A combined CCSEM/EDX, ESEM, and ICP-MS study. Journal of Geophysical Research-Atmospheres 110 (D10), D10208. Lee, H.S., Wadden, R.A., Scheff, P.A., 1993. Measurement and evaluation of acid air pollutants in Chicago using an annular denuder system. Atmospheric Environment 27A, 543–553.

Stroik at Great Smoky Mountains Heterogeneous interactions of HOBr, HNO 3 , O 3 , and NO 2 with deliquescent NaCl aerosols at room temperature

Jan 1998
3719-3725

M Snider In Bondville
H Abreu
Grand Canyon
M Arbough
D Jones
San Gorgonio
S Perchetti
J Brigantine
Bd Renfro
G C G Waschewsky

M. Snider in Bondville, H. Abreu at Grand Canyon, M. Arbough and D. Jones at San Gorgonio, S. Perchetti at Brigantine, and J. Renfro and B. Stroik at Great Smoky Mountains. References Abbatt, J.P.D., Waschewsky, G.C.G., 1998. Heterogeneous interactions of HOBr, HNO 3, O 3, and NO 2 with deliquescent NaCl aerosols at room temperature. Journal of Physical Chemistry A 102 (21), 3719–3725.

Chemical interactions between mineral dust particles and acid gases during Asian dust events Refinements to the particle-into-liquid sampler (PILS) for ground and airborne measurements of water soluble aerosol composition

Jan 2003
9-10

A Ooki
M Uematsu
D03201 D3 )
D A Orsini
Y L Ma
A Sullivan
B Sierau
K Baumann
R J Weber

Ooki, A., Uematsu, M., 2005. Chemical interactions between mineral dust particles and acid gases during Asian dust events. Journal of Geophysical Research-Atmospheres 110 (D3), D03201. Orsini, D.A., Ma, Y.L., Sullivan, A., Sierau, B., Baumann, K., Weber, R.J., 2003. Refinements to the particle-into-liquid sampler (PILS) for ground and airborne measurements of water soluble aerosol composition. Atmospheric Environ-ment 37 (9–10), 1243–1259.

Observations of fine and coarse particle nitrate at several rural locations in the United States

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