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Use of a Refluxing Mist Chamber for Measurement of Gas-Phase Mercury(II) Species in the Atmosphere
Abstract
As part of current efforts to understand the cycling of mercury (Hg) in the atmosphere, information is needed on its atmospheric speciation. Almost no data exists on water-soluble Hg(II) species in ambient air. A new technique for measuring gas phase water soluble Hg(II) species has been developed, utilizing a high-flow refluxing mist chamber. Extensive testing has been carried out, including attempts to rule out production of artifact Hg(II). Measurements at two locations (East-Central Tennessee and the Ohio-Indiana border) found approximately 0.05–0.15 ng/m3 of reactive Hg(II), representing ca. 3 to 5% of the total gaseous Hg. Limited tests of artifact Hg(II) production in the mist chamber by ozone oxidation and co-sampled aerosol Hg(II) suggest that the majority of the collected Hg(II) exists in ambient air in the gas phase.
... In 1995, a landmark paper was published that described the use of a mist chamber method for measuring RM and provided the first measurements of RM in ambient air [15]. A similar type of method had been attempted earlier by Brosset and Lord [16] using bubblers and long sampling times. ...
... Brosset and Lord [16] concluded that measured GOM was an artifact and better approaches were needed. The mist chamber used a single nebulizer nozzle, operated at a flow rate of 15 to 20 L min −1 , and collected samples in 20 mL of solution [15]. Stratton and Lindberg [15] reported that one-hour samples contained 50 to 200 pg RM. ...
... The mist chamber used a single nebulizer nozzle, operated at a flow rate of 15 to 20 L min −1 , and collected samples in 20 mL of solution [15]. Stratton and Lindberg [15] reported that one-hour samples contained 50 to 200 pg RM. The mist chamber was deployed at two locations, Tennessee and Indiana, and concentrations of 50 to 150 pg m −3 were reported; similar trends were observed under field conditions at the two sites, leading to the conclusion that the method provided reasonable results [15]. ...
This review focuses on providing the history of measurement efforts to quantify and characterize the compounds of reactive mercury (RM), and the current status of measurement methods and knowledge. RM collectively represents gaseous oxidized mercury (GOM) and that bound to particles. The presence of RM was first recognized through measurement of coal-fired power plant emissions. Once discovered, researchers focused on developing methods for measuring RM in ambient air. First, tubular KCl-coated denuders were used for stack gas measurements, followed by mist chambers and annular denuders for ambient air measurements. For ~15 years, thermal desorption of an annular KCl denuder in the Tekran® speciation system was thought to be the gold standard for ambient GOM measurements. Research over the past ~10 years has shown that the KCl denuder does not collect GOM compounds with equal efficiency, and there are interferences with collection. Using a membrane-based system and an automated system—the Detector for Oxidized mercury System (DOHGS)—concentrations measured with the KCl denuder in the Tekran speciation system underestimate GOM concentrations by 1.3 to 13 times. Using nylon membranes it has been demonstrated that GOM/RM chemistry varies across space and time, and that this depends on the oxidant chemistry of the air. Future work should focus on development of better surfaces for collecting GOM/RM compounds, analytical methods to characterize GOM/RM chemistry, and high-resolution, calibrated measurement systems.
... Vapor-phase mercury is the predominant physical state in relatively clean ambient air, where both vapor-phase and particulate-phase mercury generally coexist. When speciating the vapor-phase fraction, elemental mercury nearly always constitutes almost all of the mass with only minor amounts of other volatile species normally being detected (Brosset and Lord 1991;Stratton and Lindberg 1995). The speciation of mercury emitted to the atmosphere is of great importance for the atmospheric fate of mercury. ...
... According to Junge, another consequence is that concentrations of Hg(II) should not be too different from particulate phase concentrations of mercury because the particulates encompass Hg(II). However, recent measurements of RGM using newly designed techniques including treated filters, denuders, and refluxing mist chambers all show that RGM generally exceeds Hgparl at a variety of sites (Stratton and Lindberg 1995;Xiao et al. 1997;S.E. Lindberg and Stratton 1998;Ebinghaus et al. 1998) Measurements of operationally defined Total Gaseous Mercury (TGM) are being made on a routine basis at a number of sites in Europe and North America. ...
... It is then assumed that all gaseous Hg in both the waterphase and the atmosphere is Hg( 0) -which is a reasonable initial assumption because other volatile Hg species in the ambient atmosphere or in water occur only at very low concentrations (e.g. Stratton and Lindberg 1995;Bloom et al. 1996 a,b) -and that this Hg(o) partitions between water and atmosphere according to Henry's law. With regard to this, most surface lake waters seem to be supersaturated in Hg(o), which is assumed to give rise to an evasional flux. ...
Mercury is outstanding among the global environmental pollutants of continuing concern. Especially in the last decade of the 20th century, environmental scientists, legislators, politicians and the public have become aware of mercury pollution in the global environment. It has often been suggested that anthropogenic emissions are leading to a general increase in mercury on local, regional, and global scales (Lindqvist et al. 1991; Expert Panel 1994).
... Large research efforts have been put into the identification and quantification of these species over the last decades (e.g. Braman and Johnson, 1974;Brosset, 1982Brosset, , 1987Brosset and Lord, 1995;Stratton and Lindberg, 1995). ...
... In the last few years, new automated and manual methods have been developed to measure TGM (Tekran, Inc.; Urba et al., 1995), RGM (Tekran, Inc.; Stratton and Lindberg, 1995;Feng et al., 2000), and TPM Lu et al., 1998). These developments offer the possibility to determine both urban and background concentrations of TGM, RGM, and TPM (EU-Position Paper, 2001). ...
... Due to the fact that the fraction of RGM in the atmosphere is very small (<3 % of total gaseous mercury) and that no reference materials or adequate standards for the collection part of the RGM analytical systems are available, it is crucial to define precisely the methodology used. In the last time, there have been at least three collection methods used for RGM sampling: a multi-stage filter pack method (Bloom et al., 1996), a refluxing mist chamber method (Stratton and Lindberg, 1995;Lindberg and Stratton, 1998;Stratton et al., 2001), and a KCl-coated denuder method (Xiao et al., 1997;Feng et al., 2000;Landis et al., 2002a). ...
... The early methods for GOM and RM analysis relied on mist chambers, 32 and already in those early studies researchers raised concerns about possible interferences caused by the presence of ozone and aerosols in ambient air. 32,33 In addition to these wet methods, various types of filters (e.g., Teflon and quartz), plugs (e.g., quartz wool), and membranes (e.g., ion exchange) were introduced, where the collected GOM was either extracted by digestion as Hg 2+ or thermally desorbed as GEM for subsequent analysis. ...
... The early methods for GOM and RM analysis relied on mist chambers, 32 and already in those early studies researchers raised concerns about possible interferences caused by the presence of ozone and aerosols in ambient air. 32,33 In addition to these wet methods, various types of filters (e.g., Teflon and quartz), plugs (e.g., quartz wool), and membranes (e.g., ion exchange) were introduced, where the collected GOM was either extracted by digestion as Hg 2+ or thermally desorbed as GEM for subsequent analysis. 34,35 A somewhat different approach relied on tubular and annular denuders coated with gold 36 or KCl, 37 where the quantification of GOM was performed by extraction or thermal desorption. ...
... Global dispersion of natural and anthropogenic emissions is facilitated by elemental Hg (Hg°), the dominant chemical species found in the atmosphere. Hg° is volatile and long-lived (Fitzgerald et al., 1981; Slemr et al., 1981; Lindqvist et al., 1991; Slemr and Langer, 1992; Bergan et al., 1999; Lamborg et al., 2000) and removal from the atmosphere is thought to occur mostly through wet deposition of divalent ionic Hg (Lindqvist et al., 1991; Fitzgerald et al., 1991), though the formation and dry deposition of gas-phase ionic Hg ( " reactive gaseous Hg, " RGM) has recently been suggested to be an important and unrecognized component of the global cycle (Stratton and Lindberg, 1995; Schroeder et al., 1998; Mason et al., 2001). Current understanding suggests that soils and sediments act largely as sinks, though evasion of Hg° from soils and plants, and Hg/ methylHg mobilization from sediments are currently under examination (Nater and Grigal, 1992; Xiao et al., 1998; Lindberg et al., 1998; Ravichandran et al., 1998; Benoit, et al., 1999; Langer et al., updated ). ...
... Differences between the residence time found using 210 Pb or standing stock arguments (both lifetimes with respect to wet deposition) and the true residence time should be expected if dry deposition of either gas-or particle-phase forms of Hg is significant. Some research has suggested that pg m 3 levels of gas-phase ionic Hg ( " reactive gaseous Hg " or RGM) are sustained in the atmosphere and can give rise to large dry depositional fluxes (Stratton and Lindberg, 1995; Mason et al., 2001). In the sensitivity analyses conducted below, constraints on the residence time value were examined to provide additional insight into the impact of dry deposition. ...
... Global dispersion of natural and anthropogenic emissions is facilitated by elemental Hg (Hg°), the dominant chemical species found in the atmosphere. Hg°is volatile and long-lived (Fitzgerald et al., 1981;Slemr et al., 1981;Lindqvist et al., 1991;Slemr and Langer, 1992;Bergan et al., 1999;Lamborg et al., 2000) and removal from the atmosphere is thought to occur mostly through wet deposition of divalent ionic Hg (Lindqvist et al., 1991;Fitzgerald et al., 1991), though the formation and dry deposition of gas-phase ionic Hg ("reactive gaseous Hg,"RGM) has recently been suggested to be an important and unrecognized component of the global cycle (Stratton and Lindberg, 1995;Schroeder et al., 1998;Mason et al., 2001). Current understanding suggests that soils and sediments act largely as sinks, though evasion of Hg°from soils and plants, and Hg/ methylHg mobilization from sediments are currently under examination (Nater and Grigal, 1992;Xiao et al., 1998;Lindberg et al., 1998;Ravichandran et al., 1998;Benoit, et al., 1999;Langer et al., updated). ...
... Differences between the residence time found using 210 Pb or standing stock arguments (both lifetimes with respect to wet deposition) and the true residence time should be expected if dry deposition of either gas-or particle-phase forms of Hg is significant. Some research has suggested that pg m Ϫ3 levels of gas-phase ionic Hg ("reactive gaseous Hg" or RGM) are sustained in the atmosphere and can give rise to large dry depositional fluxes (Stratton and Lindberg, 1995;Mason et al., 2001). In the sensitivity analyses conducted below, constraints on the residence time value were examined to provide additional insight into the impact of dry deposition. ...
A box model of mercury (Hg) cycling between the atmosphere and ocean is described and used to estimate Hg fluxes on a global scale (The Global/Regional Interhemispheric Mercury Model, GRIMM). Unlike previous simulations of this system, few assumptions are made concerning the rate of prominent marine biogeochemical processes affecting Hg (e.g., evasion, particle scavenging, and deep ocean burial). Instead, consistency with two observed atmospheric distributions was required: the interhemispheric gradient in total atmospheric Hg and the value for changes in the deposition of Hg from the atmosphere since industrialization observed in both hemispheres. Sensitivity analyses underscore the importance to modeling of the atmospheric lifetime of Hg, the magnitude of the interhemispheric gradient, the historical changes in Hg concentrations of various reservoirs, and vertical exchange between the surface ocean and the permanent thermocline. Results of the model indicate: lower evasional fluxes of Hg from the global ocean than previous estimates; a prominent role for particle scavenging as a removal mechanism from the surface ocean; a modest influence of dry processes (dust and gas) on Hg removal from the atmosphere; and an estimate of natural land-based sources of Hg to the atmosphere that is no more than about half that of anthropogenic sources.
... The term reactive mercury refers to divalent mercury species that easily undergoes reduction to elemental mercury in the analysis step. The RGM content of ambient air was measured using a mist chamber (MC), similar to that developed for RGM (Stratton and Lindberg, 1995). The procedure is as follows. ...
... No long distance correlation in the RGM data has been observed, however. This is probably due to a more efficient depletion of RGM due to dry deposition or wash out by rain (Stratton and Lindberg, 1995). RGM is also likely to be scavenged by dry aerosols. ...
Mercury species in air have been measured at five sites in Northwest Europe and at five coastal sites in the Mediterranean region during measurements at four seasons. Observed concentrations of total gaseous mercury (TGM), total particulate mercury (TPM) and reactive gaseous mercury (RGM) were generally slightly higher in the Mediterranean region than in Northwest Europe. Incoming clean Atlantic air seems to be enriched in TGM in comparison to air in Scandinavia. Trajectory analysis of events where high concentrations of TPM simultaneously were observed at sites in North Europe indicate source areas in Central Europe and provide evidence of transport of mercury on particles on a regional scale.
... Higher concentrations are found in industrialised regions and close to emission sources. RGM and TPM vary substantially in concentration typically from 1 to 600 pg=m 3 depending on location (Keeler et al., 1995;Stratton and Lindberg, 1995). The major sources of RGM and TPM (as well as Hg 0 Þ in urban locations are fossil fuel combustion and incinerators but secondary formation via reactions with Hg 0 may also be important. ...
... In the last few years, new automated and manual methods have been developed to measure TGM (Tekran, 1998;Urba et al., 1999), RGM (Xiao et al., 1997;Stratton and Lindberg, 1995;Sommar et al., 1999;Feng et al., 2000) and TPM (Keeler et al., 1995;Lu et al., 1998). These developments make it possible to determine both urban and background concentrations of RGM, TPM and TGM. ...
An intercomparison for sampling and analysis of atmospheric mercury species was held in Tuscany, June 1998. Methods for sampling and analysis of total gaseous mercury (TGM), reactive gaseous mercury (RGM) and total particulate mercury (TPM) were used in parallel sampling over a period of 4 days. The results show that the different methods employed for TGM compared well whereas RGM and TPM showed a somewhat higher variability. Measurement results of RGM and TPM improved over the time period indicating that activities at the sampling site during set-up and initial sampling affected the results. Especially the TPM measurement results were affected. Additional parallel sampling was performed for two of the TPM methods under more controlled conditions which yielded more comparable results.
... Methods for measuring RM are changing as concerns over artifacts or repeatability emerge or as knowledge of RM improves. Early work using mist chambers [10], filters and membranes [11], and denuders [12] naturally resulted in inter-comparison studies, especially after an automated system became commercially available from Tekran ® Instruments Corporation that improved temporal resolution. The Tekran speciation system was an important step forward because as Hg sources and oxidant chemistry of the air vary, so too do levels of RM. ...
Mercury is a persistent and toxic global contaminant that is transported through the atmosphere, deposits to terrestrial and aquatic ecosystems [...]
... Due to its chemical properties, Hg volatilization occurs at low temperature and pH (optimal at 30°C and at pH 2), and Hg is easily transferred into the atmosphere (Takeuchi et al. 2001). Atmospheric Hg is dominated by the extremely volatile form Hg 0 (generally > 95% of total airborne Hg), whereas only minor amounts of other species (mainly particulate-phase (Hg(p)) have been detected (Stratton and Lindberg 1995). Hg 0 can be oxidized into mercuric ion Hg 2+ in the Earth's atmosphere by photochemical reactions, and then it may precipitate by rainfall and dry deposition (Bacci et al. 1994;Paige Wright et al. 2016). ...
Mercury (Hg) is a highly toxic metal with no known biological function, and it can be highly bioavailable in terrestrial ecosystems. Although fungi are important contributors to a number of soil processes including plant nutrient uptake and decomposition, little is known about the effect of Hg on fungi. Fungi accumulate the largest amount of Hg and are the organisms capable of the highest bioaccumulation of Hg. While referring to detailed mechanisms in bacteria, this mini-review emphasizes the progress made recently on this topic and represents the first step towards a better understanding of the mechanisms underlying Hg tolerance and accumulation in fungal species and hence on the role of fungi within the Hg cycle at Hg-contaminated sites.
Key points
• The fungal communities are more resilient than bacterial communities to Hg exposure.
• The exposure to Hg is a threat to microbial soil functions involved in both C and nutrient cycles.
• Fungal (hyper)accumulation of Hg may be important for the Hg cycle in terrestrial environments.
• Understanding Hg tolerance and accumulation by fungi may lead to new remediation biotechnologies.
... Gold amalgamation preconcentration, followed by thermal desorption (TD) in Ar carrier gas and detection via atomic fluorescence spectrometry (AFS), is a commonly used method for quantifying atmospheric elemental mercury vapor, Hg 0 (g) (hereafter referred to as gaseous elemental mercury, GEM) (Schroeder et al., 1995;Gustin and Jaffe, 2010;Pandy et al., 2011). Coupled with various sample capture and pretreatment methods, the above measurement scheme is also used for quantitative analysis of atmospheric gaseous oxidized mercury (GOM) (Stratton and Lindberg, 1995;Landis et al., 2002;Lyman et al., 2007), total gaseous mercury (TGM ≡ GEM + GOM) , atmospheric particle-bound mercury (PBM) (Landis et al., 2002), atmospheric total mercury (THg ≡ GEM + GOM + PBM) (Jaffe et al., 2005), and total aqueous Hg (USEPA, 2002). Most AFS-based atmospheric Hg measurements employ Tekran ® Instruments Corporation's model 2537 Hg vapor analyzers (versions A and B; hereafter referred to collectively as "the Tekran ® analyzer") (Schroeder et al., 1995;Landis et al., 2002;Tekran Corporation, 2006, 2007. ...
Atmospheric Hg measurements are commonly carried out using
Tekran® Instruments Corporation's model 2537
Hg vapor analyzers, which employ gold amalgamation preconcentration sampling
and detection by thermal desorption (TD) and atomic fluorescence spectrometry (AFS). A
generally overlooked and poorly characterized source of analytical
uncertainty in those measurements is the method by which the raw Hg atomic
fluorescence (AF) signal is processed. Here I describe new software-based methods
for processing the raw signal from the
Tekran® 2537 instruments, and I evaluate the
performances of those methods together with the standard
Tekran® internal signal processing method.
For test datasets from two Tekran®
instruments (one 2537A and one 2537B), I estimate that signal processing
uncertainties in Hg loadings determined with the
Tekran® method are within
±[1 % + 1.2 pg] and ±[6 % + 0.21 pg],
respectively. I demonstrate that the Tekran®
method can produce significant low biases (≥ 5 %) not only at low
Hg sample loadings (< 5 pg) but also at tropospheric background
concentrations of gaseous elemental mercury (GEM) and total mercury (THg)
(∼ 1 to 2 ng m−3) under typical operating conditions (sample
loadings of 5–10 pg). Signal processing uncertainties associated with the
Tekran® method can therefore represent a
significant unaccounted for addition to the overall ∼ 10 to 15 %
uncertainty previously estimated for
Tekran®-based GEM and THg measurements.
Signal processing bias can also add significantly to uncertainties in
Tekran®-based gaseous oxidized mercury (GOM)
and particle-bound mercury (PBM) measurements, which often derive from Hg
sample loadings < 5 pg. In comparison, estimated signal processing
uncertainties associated with the new methods described herein are low,
ranging from within ±0.053 pg, when the Hg thermal desorption peaks are
defined manually, to within ±[2 % + 0.080 pg] when peak
definition is automated. Mercury limits of detection (LODs) decrease by 31 to
88 % when the new methods are used in place of the
Tekran® method. I recommend that signal
processing uncertainties be quantified in future applications of the
Tekran® 2537 instruments.
... Gold amalgamation pre-concentration, followed by thermal desorption (TD) in Ar carrier gas and detection via atomic fluorescence spectrometry (AFS) is a commonly used method for quantifying atmospheric elemental mercury vapor, Hg 0 (g) (hereafter referred to as gaseous elemental mercury, GEM) (Schroeder et al., 1995;Gustin and Jaffe, 2010;Pandy et al., 2011). 25 Coupled with various sample capture and pre-treatment methods, the above measurement scheme is also used for quantitative analysis of atmospheric gaseous oxidized mercury (GOM) (Stratton and Lindberg, 1995;Landis et al., 2002;Lyman et al., 2007), total gaseous mercury (TGM ≡ GEM + GOM) (Ambrose et al., 2015), atmospheric particle-bound mercury (PBM) (Landis et al., 2002), atmospheric total mercury (THg ≡ GEM + GOM + PBM) (Jaffe et al., 2005), and total aqueous Hg vapor analyzers (versions A and B; hereafter referred to collectively as 'the Tekran ® analyzer') (Schroeder et al., 1995;Landis et al., 2002;Tekran Corporation, 2006, 2007. ...
Atmospheric Hg measurements are commonly carried out using Tekran® Instruments Corporation's model 2537 Hg vapor analyzers, which employ gold amalgamation pre-concentration sampling and detection by thermal desorption/atomic fluorescence spectrometry. A generally overlooked and poorly characterized source of analytical uncertainty in those measurements is the method by which the raw Hg atomic fluorescence signal is processed. Here I describe new software-based methods for processing the raw signal from the Tekran® 2537 instruments, and I evaluate the performances of those methods together with the standard Tekran® internal signal processing method. For test datasets from two Tekran® instruments (one 2537A and one 2537B), I estimate that signal processing uncertainties in Hg loadings determined with the Tekran® method are within ±[6 % + 0.94 pg]. I demonstrate that the Tekran® method produces significant low biases (≥ 5 %) not only at low Hg sample loadings (3) under typical operating conditions (sample loadings of 5–10 pg). Signal processing uncertainties associated with the Tekran® method therefore represent a significant unaccounted for addition to the overall ~ 10 to 15 % uncertainty previously estimated for Tekran®-based GEM and THg measurements. In comparison, estimated signal processing uncertainties associated with the new methods described herein are low, ranging from within ±0.053 pg, when the Hg thermal desorption peaks are defined manually, to within ±[2 % + 0.080 pg] when peak definition is automated. Mercury limits of detection decreased by ~ 31 to 88 % when the new methods were used in place of the Tekran® method. I recommend that signal processing uncertainties be quantified in future applications of the Tekran® 2537 instruments.
... Background concentrations of different TGM averaging about 1.5 ng m -3 in background air throughout the world [9][10], the area characterized to higher emission register the higher concentration. The concentration of other monitored form, such as RGM (Reactive Gas phase Mercury) and TPM (Particulate Mercury as Total), vary from 1 to 600 pg m -3 ([11]; [12]; [13]; [14]; [15]). The rainy event allow the removal of RGM compounds that are water-soluble, the lifetime of RGM is in fact of days or some weeks [16]. ...
The chemistry of mercury, in reference to its behavior in the atmosphere, is more complex compared to other heavy metals. Main forms are: elemental mercury vapor (Hg0, called even or zerovalent metallic mercury), mercury vapor divalent (Hg22+ mercurous, or Hg2+ mercuric), organic mercury (especially methylmercury, MeHg). A fourth form could be considered, different under the chemical profile, whose characteristic is physical: mercury bound to particulate (HgP), in the form of Hg0 and Hg2+. In general, analyses on ambient air are performed on the Total Gaseous Mercury (TGM) which is defined as the fraction passing a 0.45 μm filter; TGM is mainly composed of elemental Hg0 vapour, with minor fractions of other volatile forms as HgCl2, CH3HgCl or (CH3)2Hg. Measurements carried out at background sites reveal that the TGM corresponds almost to total mercury (>99%) in atmosphere. Global anthropogenic emission for North America, Europe and East Europe areas data indicate that stationary combustion processes, are responsible of about 60-75% of all mercury emitted, mainly because of its content in coal, for a total of 2000 tons/year. About 50 % of emissions from combustion of fossil fuels is constituted by Hg0, 40 % of Hg2+ and 10 % of HgP. Mercury is therefore assumed as a tracer of coal combustion emission. The official Italian sampling and analysis procedure (DLgs 155/10 - UNI EN 15852) has been tested as is, and modified in order to improve the analytical performance, reduce the timing requirement and reduce the related cost. All the variations introduced have been thoroughly investigated in order to exclude any negative effect on the standard performances.
... Mist chamber and denuders (tubular denuders and annular denuders) are generally used for the sampling of RGM. Aqueous solution containing 0.1 M HCl is filled in the mist chamber and shielded from sunlight with aluminium foil to collect RGM ( generally at the flow rate of 12 L/min) (Stratton and Lindberg, 1995;Munthe et al., 2001). The collected mercury is detected by SnCl 2 -CVAFS method. ...
Mercury (Hg) is a highly toxic metal, which is known as a global pollutant due to its ability to undergo long-range transport in the atmosphere. Methylated mercury can pose serious adverse effects on human health and environment. Mercury is emitted into the atmosphere by various natural and anthropogenic sources. The largest anthropogenic source of mercury is coal combustion, which contributes ~62% of global emissions. Total global emissions of atmospheric mercury are estimated to be 5600 Mg/year from natural and anthropogenic sources, respectively, contributing around 37% and 63% of total atmospheric mercury. About 40% of global anthropogenic emissions are contributed by East and Southeast Asia with the largest emissions from China (75%) followed by South America and Sub-Saharan Africa. Latter regions are mainly responsible due to increase in artisanal and small scale gold mining. The present estimates of mercury emissions have large uncertainties in global budget, which are mainly due to lack of knowledge of mercury exchange between various components of ecosystem with its speciation in spatial and temporal distribution. Special efforts are needed in the regions of growing economy especially in South Asia where atmospheric mercury is almost unattempted. In order to reduce uncertainties and get more realistic emission figures, there is need to develop an extensive monitoring network to measure various forms of mercury in air, soil and aquatic systems in south Asia. Controlling the emissions of global atmospheric mercury is a big challenge to the scientists and policymakers. Probably, it can be achieved by focusing on implementation of the available technologies and by developing new technologies for mercury removal through developing an extensive partnership between industries and governmental organizations.
... In contrast, automated samplers provide short time (seconds to minutes) resolution measurements and do not need measurements by an alternate method. Stratton and Lindberg (1995), Lindberg and Stratton (1998), Lindberg et al. (2000), and Stratton et al. (2001) described development of a mist chamber for measurement of GOM (termed RGM then). The principle of operation includes pulling air at a high flow rate (15 to 20 Lpm) through a fine mist aerosol made of water, NaCl, and HCl. ...
Measurements of atmospheric mercury (Hg) are being increasingly incorporated into monitoring networks worldwide. These data are expected to support and inform regulatory decision making aimed at protecting human and wildlife health. Here we critically review current efforts to measure Hg concentrations in the atmosphere and interpret these data with Hg models. There are three operationally defined forms of atmospheric Hg: Gaseous Elemental (GEM), Gaseous Oxidized (GOM), and Particulate Bound (PBM). While there is relative confidence in GEM measurements, GOM and PBM are less well understood. Field and laboratory investigations suggest the methods to measure GOM and PBM are impacted by analytical interferences that vary with environmental setting (e.g., ozone, relative humidity) and GOM concentrations can be biased low by a factor of 1.6–12 times depending on the chemical compound. Importantly, efforts to understand the fundamental limitations of atmospheric Hg measurement methods have provided clear evidence that the composition of GOM (e.g., HgBr2, HgCl2, HgBrOH) varies across space and time. This has significant implications for refining existing measurement methods and developing new ones, model/measurement comparisons, model development, and assessing trends. In addition, unclear features of previously published data may now be re-examined and possibly explained, which we present as a case study. Lastly, we outline recommendations for needed research directions as the Hg field moves forward. Priorities include GOM and PBM calibration systems, identification of GOM compounds in ambient air, and identification of redox mechanisms and associated rate coefficients. Determination of a quantitative correction factor for biased GOM and PBM data is also needed to facilitate model-measurement comparisons.
... The extraction of RGM is commonly based on either the high solubility of the target compounds in aqueous solution, or their ability to form complexes with crystalline halogen surfaces. Slightly acidified refluxing mists 58 and KCl coated denuders 59,60 are the most commonly used pre-concentration media for this purpose. Both approaches may be combined with cold vapour formation using SnCl 2 , or NaBH 4 , and detection by atomic fluorescence spectrometry (CV-AFS). ...
... The past fifteen years have brought many advances in measuring trace levels of Hg(II) in environmental samples using chemical methods (Bloom and Crecelius, 1983;Stratton and Lindberg, 1995). However, these methods do not provide information on the fraction of Hg(II) that is bioavailable to bacteria and therefore has the potential to be biotically methylated to MeHg or microbially reduced to Hg 0 . ...
... The initial objective of this component of my research was to determine the bioavailability of Hg(II) in snow entering the Arctic via long-range atmospheric transport. In addition to samples for bioHg, snow samples were collected for total Hg, Me Hg, and major cation chemistry. Polar sunrise at Barrow is in late January, and the melt period begins in June. Samples were therefore collected before Polar sunrise in January and after Polar sunrise in March, May, and June 2000. BioHg was undetectable in Barrow snow in January, and total Hg concentrations were low. BioHg then increased from 0.22 ng/L (~1% of total Hg) in March to 8.8 ng/L (nearly 13% of the total Hg) in May (Fig. 2). (Rarely have the environmental samples that I have analyzed exceeded 0.5 ng/L.) Our June snow sample was taken just before the intensive snowmelt period began, so the snow was slushy but not melted. BioHg had decreased to 2.9 ng/L, which is still very high for a remote area. Furthermore, this concentration represented over 50% of the total Hg in Barrow snow. Because Barrow has sunlight 24 hours a day during the melt period, melting occurs over a relatively short time. If these concentrations of bioHg are sustained during this period, a very large pulse must be entering the ecosystem in the spring. (We will be examining the melt period more intensively in 2001; see below.) An interesting and unexpected finding was that during Polar sunrise, MeHg also increased to concentrations commonly found in boreal wetlands where it is biotically produced. The mechanism of MeHg formation in the Arctic atmosphere is as yet unknown; however, we hypothesize that it could involve the demethylation of dimethyl mercury (diMeHg) produced biogenically in the ocean....
... As a result, simple analogies of Hg(0) uptake with that of other common gases such as O 3 , SO 2 , and NO 2 are inappropriate . Another potential source of Hg is RGM (Stratton and Lindberg 1995). Because of its high deposition velocity, this Hg species would accumulate in foliage (Barton et al. 1981;Guentzel et al. 1998). ...
This review focuses on mercury (Hg) inputs and outputs in temperate and boreal terrestrial systems. It covers deposition via throughfall and litterfall, whose sum (ca. 38 μg m-2 a-1) is greater than that via precipitation (ca. 10 μg m-2 a-1). Outputs considered include volatilization, soil sequestration, and streamflow. The former is highly uncertain, but the mean rate (11 ng m-2 h-1) over a growing season is equivalent to about 32 μg m-2 a-1. Modern rates of soil sequestration (ca. 5 μg m-2 a-1) and streamflow fluxes (ca. 2 μg m-2 a-1) balance the annual budget. The majority of the uncertainty in the budget is related to volatilization. Nonetheless, a large fraction of atmospheric Hg is likely a product of continuing deposition and volatilization. Watershed characteristics related to streamflow fluxes of both Hg and methylmercury (MeHg) are discussed. Both runoff concentration and flux of Hg are weakly and inversely related to watershed size. Dissolved organic carbon (DOC) and particulates are important carriers of Hg; watershed activities that affect either affect Hg flux. Runoff flux of MeHg is skewed with about 80% of observations less than 0.15 μg m-2 a-1. Although there is no pattern of MeHg flux with watershed size, there is a strong positive relationship between flux and wetland area. Wetlands are a site of MeHg production and their presence increases water residence time; both increase MeHg flux. Concentrations of MeHg in streamflow from watersheds with wetlands are near the current water quality criterion, and effective control measures in those watersheds appear problematic.
... Methods applied for measurement of GOM have included KCl-coated tubular and annular denuders; 13,17,18 mist chambers; 19 and cation exchange membranes (CEM). 20−26 Methods applied for PBM measurements include particulate traps 9,27 and filter packs. ...
The chemical compounds that make up gaseous oxidized mercury (GOM) in the atmosphere, and the reactions responsible for their formation, are not well understood. The limitations and uncertainties associated with the current method applied to measure these compounds, the KCl-coated denuder, are not known due to lack of calibration and testing. This study systematically compared the uptake of specific GOM compounds by KCl-coated denuders with that collected using nylon and cation exchange membranes in the laboratory and field. In addition, a new method for identifying different GOM compounds using thermal desorption is presented. Different GOM compounds (HgCl2, HgBr2, and HgO) were found to have different affinities for the denuder surface and the denuder underestimated each of these compounds. Membranes measured 1.3 to 3.7 times higher GOM than denuders in laboratory and field experiments. Cation exchange membranes had the highest collection efficiency. Thermodesorption profiles for the release of GOM compounds from the nylon membrane were different for HgO versus HgBr2 and HgCl2. Application of the new field method for collection and identification of GOM compounds demonstrated these vary as a function of location and time of year. Understanding the chemistry of GOM across space and time has important implications for those developing policy regarding this environmental contaminant.
... Greater than 95% of mercury exists as gas-phase elemental mercury (Fitzgerald and Gill, 1979;Bloom and Fitzgerald, 1988;Iverfeldt, 1991a). There is growing evidence to suggest that some chemical form of Hg 2þ also exists in the gas phase (the so-called "reactive gaseous mercury" or RGM; Stratton and Lindberg, 1995;Sheu and Mason, 2001;Landis et al., 2002). Concentrations of total gaseous mercury (TGM; including elemental, ionic and gaseous alkylated forms such as dimethylHg) in remote areas are typically in the range of 1 -2 ng (as mercury) m 23 . ...
Mercurial, the metaphor for volatile unpredictable behavior, aptly
reflects the complexities of one of the most insidiously interesting and
scientifically challenging biogeochemical cycles at the Earth's surface.
Elemental mercury is readily recognized as a silvery liquid at room
temperature. Its gas phase is important geochemically, since mercury and
some of its compounds have relatively high vapor pressures. Mercury (Hg,
from the Latin hydrargyrum or "watery silver") is sulfur loving (i.e.,
chalcophilic) and extremely active biologically. It is mobilized
tectonically, and significant deposits are found in mineralized regions
characterized by subduction zones and deep-focus earthquakes
(Schlüter, 2000). Many of the major deposits are shown in Figure 1
(Kesler, 1994).
... The most common gaseous forms of Hg are elemental Hg (Hg 0 ) and dimethyl-Hg ((CH 3 ) 2 Hg). On a global scale, the atmospheric Hg cycle is dominated by elemental Hg (generally > 95% of total airborne Hg), whereas only minor amount of other species (mainly particulate-phase Hg (Hg(p)) have been detected (Stratton and Lindberg, 1995). Both methyl-Hg and dimethyl-Hg have been detected in ambient air (Bloom and Fitzgerald, 1988). ...
... This need brought about the development of three methods to determine RGM concentrations in ambient air. These methods are mist chambers (Lindberg and Stratton, 1998;Stratton and Lindberg, 1995;Stratton et al., 2001), ion-exchange filters (Ebinghaus et al., 1999), and collection on KCl denuders (Landis et al., 2002b, Xiao, 1997 In-situ air samples were collected on the roof of the administration building at Rosenstiel School of Marine and Atmospheric Science. Samples were collected on a KCl manual sampling assembly for 30 min to 6 hours at a sample rate of 10 L min -1 . ...
Over the last decade our understanding of mercury cycling has dramatically changed. Evidence of rapid atmospheric oxidation has been observed in numerous locations. Observations show that Hg0 can undergo rapid gas-phase oxidation under atmospheric conditions. The mechanism and importance of this transformation is still unclear. This work determined kinetic rate coefficients for the potentially important mercury reactions. Rate coefficients were determined using a Pulse Laser Photolysis -- Laser Induced Fluorescence (PLP-LIF) technique monitoring one or more of the following species, Hg0, Cl, Br, HgCl, and HgBr. The concentrations of these species were measured by LIF a producing concentration vs. time profiles, from these profiles a rate coefficient for the reaction can be obtained. In this work kinetic rate coefficients for the following reactions were measured. Hg0+Cl+M-->HgCl+ M Hg0+Br+M-->HgB r+M HgBr+M-->Hg0+B r+M HgBr+Br-->products HgCl+O2-->prod ucts This work was the first direct measurement of a kinetic rate coefficient for these reactions, and the first work which employed one photon LIF to monitor the HgCl and HgBr products. This work also developed new laser based techniques to detect mercury and its oxidation products for both laboratory and field application. A LIF technique was developed to detect HgCl and HgBr, and a further developed a two photon LIF technique. The two photon LIF technique was used to directly monitor Hg0 atoms, to monitor Hg0 evolving form a gold tube, and to monitor the Hg0 evolving from the thermal decomposition of reactive gaseous mercury collected on a denuder. This work represents significant advances in the development of viable methods the detect mercury and mercury oxidation products for laboratory and field studies, and is the first study to observe clear differences in the characteristic desorption profiles of HgO and HgX2. This work has broad implications; it enhanced our current knowledge concerning the biogeochemical cycling of mercury, broadened our understanding of the mercury chemistry in high halogen environment, and provided new techniques to use in both field and laboratory studies.
... There are few "eld measurements available to compare with the modeled ambient Hg(II) concentrations. Mean Hg(II) concentration measurements varied from 0.045 in Tennessee to 0.27 ng m\ in Indiana (Stratton and Lindberg, 1995), and fall within the range of 0.03}0.32 ng m\ obtained from the model simulation. ...
A three-dimensional regional scale air quality model was developed to study the atmospheric transport, transformation and deposition of mercury (Hg) by formulating and incorporating mercury chemistry, cloud processes, and air–surface exchanges into the framework of Sarmap Air Quality Model (SAQM). Three mercury species were included: elemental mercury Hg(0), divalent mercury Hg(II), and particulate mercury Hg(p). Precipitating clouds, co-existing non-precipitating clouds, and fair weather clouds were considered in modeling the in-cloud transformation processes. A formulation of bi-directional air-surface exchange of elemental mercury was used for emission from, and dry deposition to, natural surfaces. Preliminary evaluation of the model was conducted by comparing six major weekly output variables, including ambient Hg concentrations and Hg concentration in precipitation, with corresponding measurements at eight monitoring stations in Connecticut for a summer week and a winter week. Model predictions of surface-level gaseous Hg concentrations were close to measured levels, agreeing to within 12% on average, about half the estimated error in measurements. The predicted Hg concentrations in precipitation were 50% higher than measured values on average, slightly lower than the estimated 60% error in measurements. The model was shown to be capable of predicting hourly concentrations and deposition fields of the three Hg species as well as in-cloud transformation of Hg(0) by each of the three cloud types, and useful in analyzing the effects of various controlling factors on the transport and transformation of Hg species in the atmosphere.
... A Gardis automatic TGM analyser was used at Site 3 and at Site 2 a Tekran automatic TGM analyser was employed. The RGM content of ambient air was measured using a mist chamber (MC) (Stratton and Lindberg, 1995). At Sites 2 and 3 denuders (Xiao et al., 1997) were also employed to determine RGM ambient concentrations. ...
The Mediterranean Atmospheric Mercury Cycle System (MAMCS) project was performed between 1998 and 2000 and involved the collaboration of universities and research institutes from Europe, Israel and Turkey. The main goal of MAMCS was to investigate dynamic processes affecting the cycle of mercury in the Mediterranean atmosphere by combining ad hoc field measurements and modelling tasks. To study the fate of Hg in the Mediterranean Basin an updated emission inventory was compiled for Europe and the countries bordering the Mediterranean Sea. Models were developed to describe the individual atmospheric processes which influence the chemical and physical characteristics of atmospheric Hg, and these were coupled to meteorological models to examine the dispersion and deposition of Hg species in the Mediterranean Basin. One intercomparison and four two-week measurement campaigns were carried out over a three-year period. The work presented here describes the results in general terms but focuses on the areas where definite conclusions were unforthcoming and thus highlights those aspects where, in spite of advances made in the understanding of Hg cycling, further work is necessary in order to be able to predict confidently Hg and Hg compound concentration fields and deposition patterns.
... Mist chambers, containing a KCl/HCl solution may also be used to trap RGM. With this approach air is drawn through a glass chamber containing a fine dispersed liquid aerosol that continuously is formed from a refluxing KCl/HCl solution (Stratton and Lindberg, 1995;Stratton et al., 2001). The solution is then analysed using SnCl 2 reduction and CVAFS. ...
An evaluation of mercury observations from North Sea coastal stations during 1995–2002 has been performed. The mercury data originate from EMEP/OSPAR stations in Ireland, Netherlands, Germany, Norway and Sweden where mercury in precipitation and Total Gaseous Mercury (TGM) have been measured. A decreasing trend in mercury wet deposition is observed. The decrease is sufficiently large to be significant considering measurement precision and appears to occur at all the studied sites. The reduction in deposition is 10–30% when comparing the two periods 1995–1998 and 1999–2002. The trend is likely to be due to emission controls in Europe. In contrast, no decreasing trend in TGM could be observed during the same time periods. A plausible explanation is that the TGM concentration measured in the OSPAR area to a larger extent than before is dominated by the hemispherical background concentration of TGM.
Accurately measuring reactive gaseous mercury (RGM) concentrations in the atmosphere is important for better understanding of global mercury (Hg) cycle. In this study, we compared the RGM collection efficiencies of four sampling methods, including a 14 cm long KCl-coated denuder, KCl-coated glass fiber filter, KCl-coated quartz sand tube and cation exchange membrane. Both laboratory studies and field RGM monitoring were carried out in environments with low humidity (relative humidity (RH) of ~20%), medium humidity (RH of 50-70%) and high humidity (RH of ~100%). Laboratory results showed that in environments with RH lower than 70%, RGM amounts collected by KCl-coated glass fiber filter and KCl-coated quartz sand tube were comparable with those collected by cation exchange membrane. In environments with RH of ~100%, cation exchange membrane collected greater RGM amount, about 1.1-1.4, 1.1-1.2 and 2.4-2.7 times as high as that by KCl-coated glass fiber filter, KCl-coated quartz sand tube and KCl-coated denuder, respectively. During field monitoring, RGM amounts collected by KCl-coated quartz sand tube were comparable to cation exchange membrane irrespective of RH in the environment (p>0.05, n=60). Large variations (up to 20 during field monitoring) in RGM concentrations measured by different sampling methods indicate the need for a unified and standardized method for future RGM monitoring.
This review presents the conclusions of recent international studies pertaining to the speciation, emission sources, and fate of mercury in the atmosphere. The background level of total gaseous mercury concentration in the air is 1-3 ng m⁻³. Mercury takes various physical and chemical forms in the atmosphere, mainly gaseous elemental mercury [Hg (0)], gaseous divalent mercury [Hg (II)], particulate mercury [Hg (p)]. Hg (0) is the dominant form of mercury in the atmosphere and the concentrations of Hg (II) and Hg (p) are generally only a few percent of the total concentration of airborne mercury. Because these three species have different characteristics with respect to transport, deposition, and influences on ecosystems, mercury speciation measurements are of great importance. Mercury is emitted from natural and anthropogenic sources. Natural sources include volcanic activity and evasion from sea, soil and vegetation surfaces. Anthropogenic sources include coal combustion, waste incineration, and non-ferrous metal refining and smelting. Mercury emitted from these sources into the atmosphere is removed by wet and dry deposition. Wet deposition is the main process of mercury removal from the atmosphere. In this process, atmospheric oxidation processes in which Hg (0) is converted to Hg (II) by O3, H2O2, and Cl2 play important roles.
Gaseous elemental mercury (GEM, Hg) emissions are transformed to divalent reactive Hg (RM) forms throughout the troposphere and stratosphere. RM is often operationally quantified as the sum of particle bound Hg (PBM) and gaseous oxidized Hg (GOM). The measurement of GOM and PBM is challenging and under mounting criticism. Here we intercompare six months of automated GOM and PBM measurements using a Tekran® (TK) KCl-coated denuder and quartz regenerable particulate filter method (GOMTK, PBMTK, and RMTK) with RMCEM collected on cation exchange membranes (CEMs) at the high altitude Pic du Midi Observatory. We find that RMTK is systematically lower by a factor of 1.3 than RMCEM. We observe a significant relationship between GOMTK (but not PBMTK) and Tekran® flushTK blanks suggesting significant loss (32%) of labile GOMTK from the denuder or inlet. Adding the flushTK blank to RMTK results in good agreement with RMCEM (slope=1.01, r2=0.90) suggesting we can correct bias in RMTK and GOMTK. We provide a bias corrected (*) Pic du Midi dataset for 2012-2014 that shows GOM* and RM* levels in dry free tropospheric air of 198±57 and 229±58 pg m-3 which agree well with in-flight observed RM and with model based GOM and RM estimates.
Atmospheric sources are recognized to be significant in the cycling of Hg in the biosphere, yet there are few reliable data on air/surface exchange rates of Hg in forests. We have developed a tower-based micrometeorological method for measuring gas-phase Hg fluxes over environmental surfaces, and have used this approach to measure Hg° fluxes over soils, vegetation, and water surfaces. These fluxes have been combined with modeling results based on measurements of atmospheric Hg concentrations and speciation to quantify the overall flux of Hg between the atmosphere and the ground. These results are compared with a study of the biogeochemical cycle of Hg in the temperate deciduous forest at Walker Branch Watershed in the southeastern United States. Our preliminary results suggest that the largest Hg fluxes in forests involve gas exchange at the air/vegetation interface. Given the magnitude of these fluxes and their level of uncertainty, this forest could act as a net source or sink for atmospheric Hg, indicating the importance of better understanding the role of Hg exchange at the vegetation surface.
This article reviews current knowledge of atmospheric mercury processes and describes activities in Europe and North America to simulate these processes by means of tropospheric chemistry/transport models for regional-scale applications. Advantages and limitations of relatively simple Lagrangian models are discussed within the context of issues currently facing the environmental scientific and policymaking communities. The current state and future direction of comprehensive Eulerian models in simulating the tropospheric chemistry and transport of mercury species is outlined. A number of central improvements in these models are discussed, with consideration of the key progress necessary to include feedbacks and interactions between formation and distribution of clouds and mercury atmospheric chemistry.
Due to special physicochemical property and extreme toxicity, mercury is regarded as a global pollutant. The progress on the emission sources of mercury to the air, the distribution and speciation of mercury in ambient air in the global scale and the transformation of mercury in the troposphere is critically reviewed. We also highlighted the future research needs regarding mercury cycling in the global atmosphere. The new achievements on mercury biogeochemical cycling in aquatic systems are summarized and it is pointed out that more study is urgently needed to scrutinize the mechanism of mercury methylation in aquatic systems. The status of mercury pollution to the local environment and it impacts on human health in mercury mining and gold mining areas are summarized, and the major pathway of mercury exposure to local inhabitants are pointed out. Finally, we summarize the recent progress on the health impacts of people who exposed to different mercury species.
Mercury occurs naturally in the Earth’s crust principally as the ore, cinnabar, HgS. Mercury is quite different from other metals in several respects: (i) it is the only metal that is liquid at room temperature; (ii) it is the only metal that boils below 650°C; (iii) it is quite inert chemically, having a higher ionization potential than any other electropositive element with the sole exception of hydrogen; (iv) it exists in oxidation states of zero (Hg°) and 1 (Hg22+) in addition to the expected state of 2 (Hg2+). Mercury forms alloys (“amalgams”) with many metals. Mercury and its chemical derivatives are extremely hazardous. Since the early 1960s, the growing awareness of environmental mercury pollution (e.g. the Minamata tragedy resulting from methyl-mercury poisoning) has stimulated the development of more accurate, precise and efficient methods of determining mercury and its compounds in wide variety of matrices.
Baltimore's urban air is a potentially important source of mercury (Hg) to the northern Chesapeake Bay. Elevated total atmospheric Hg (THg) concentrations were detected at a sampling site in downtown Baltimore (4.4±2.7 ng/m3), as compared to a rural site (1.7±0.5 ng/m3). The urban air was also enriched with reactive gaseous Hg (RGHg) and particulate-bound Hg (Hg-P). The annual dry depositional fluxes of RGHg and Hg-P at sites around the northern Chesapeake Bay have been determined, with the fluxes of RGHg ranging from 7 to 121 µg/m2 and the fluxes of Hg-P from 1 to 34 µg/m2. These values were the same magnitude as the wet depositional fluxes of Hg measured at the same sites. Local wind direction influenced the concentration of atmospheric Hg detected at the urban sampling site. When air came from the SE, S and SW directions, the urban sampling site tended to be impacted by the local emission sources, with higher THg and Hg-P concentrations detected.
Mercury (Hg) is a global health concern due to its toxicity and ubiquitous presence in the environment. Here we review current methods for measuring the forms of Hg in the atmosphere and models used to interpret these data. There are three operationally defined forms of atmospheric Hg: gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particulate bound mercury (PBM). There is relative confidence in GEM measurements (collection on a gold surface), but GOM (collection on potassium chloride (KCl)-coated denuder) and PBM (collected using various methods) are less well understood. Field and laboratory investigations suggest the methods to measure GOM and PBM are impacted by analytical interferences that vary with environmental setting (e.g., ozone, relative humidity), and GOM concentrations measured by the KCl-coated denuder can be too low by a factor of 1.6 to 12 depending on the chemical composition of GOM. The composition of GOM (e.g., HgBr2, HgCl2, HgBrOH) varies across space and time. This has important implications for refining existing measurement methods and developing new ones, model/measurement comparisons, model development, and assessing trends. Unclear features of previously published data may now be re-examined and possibly explained, which is demonstrated through a case study. Priorities for future research include identification of GOM compounds in ambient air and development of information on their chemical and physical properties and GOM and PBM calibration systems. With this information, identification of redox mechanisms and associated rate coefficients may be developed.
Tropospheric mercury is dominated by gas phase species. In this paper, the gas phase reactions between the nitrate radical and volatile biogenic mercury species have been investigated. An upper limit for the gas phase rate coefficient for reaction between elemental mercury and NO3-radicals was determined to 4 × 10−15 cm3 molecule−1 s−1 by using the fast flow-discharge technique. The reaction between dimethyl mercury and NO3, previously shown to be rapid, has also been studied in the laboratory with respect to product distribution using FT-IR. The result from the product study is consistent with a transformation of dimethyl mercury into inorganic, divalent mercury. All carbon delivered as dimethyl mercury was transformed into formaldehyde, methanol and methyl peroxynitrate. Hg was observed as a minor (≈2%) product. By exclusion, HgO is proposed as the mercury-containing product. Thus, the reaction between dimethyl mercury and the nitrate radical is excluded as a source of monomethyl mercury species in the atmosphere.
The concentration of total atmospheric gaseous mercury (TGM) and total particulate mercury (TPM) have been measured during one summer campaign (19–29 August 2003) and one winter campaign (26 January–3 February 2004) at a rural site in Poland. Mercury deposition was also measured using bulk samplers. The measurement campaigns were performed in a typical agricultural area of Southern Poland where 85% of the houses use low capacity domestic heating units (DHUs) fuelled with hard coal during the cold season. An average TGM value of 1.63±0.35ngm-3 was obtained in the summer campaign, whereas a 2.5 times higher TGM concentration was found during winter. The mean TPM concentration during summer was 0.11±0.05ngm-3 while 10 times higher values were obtained during the winter campaign. The mercury deposition was also found to be much higher during winter in comparison to summer. The summer TGM values are at the same level as the annual average TGM at background locations in most West European countries including Scandinavia. The higher TGM values in winter are most likely due to the use of DHUs in the local area. However, both summer and winter TPM concentrations and mercury deposition fluxes are much higher than in most neighbouring West European countries. This probably reflects the regional use of coal combustion for electric energy production and in low-capacity DHUs.
A species specific isotope dilution (SSID) method for determination of the volatile mercury (Hg) species Hg0, (CH3)2Hg, CH3HgX and HgX2
(where X is a counter ion) in gaseous samples was developed. The procedure involved on line derivatisation of ionic Hg species with sodium tetraethylborate during sampling, before collection of species on a Tenax TA tube in series with an Au–Pt tube. Collected species were thermally desorbed and determined by GC-ICP-MS. The procedure provided absolute detection limits of 0.5 pg for CH3HgX and (CH3)2Hg, 5 pg for HgX2 and 25 pg for Hg0. Recoveries and transformations of the investigated species were studied for the different procedural steps and the method was tested for microcosm experiments on brackish water sediment samples, as well as for laboratory air samples. As a result of methylation and reduction processes within the sediment, gaseous emission rates could be determined for all investigated species after addition of an isotope enriched aqueous inorganic 199Hg2+ standard to the sediment. Hg0 was the only specie detected in laboratory air samples (4.5 ng m−3). The procedure for derivatisation of ionic Hg species prior to collection on Tenax TA reduces memory effects and transformations of CH3HgX and HgX2, which is especially advantageous at low sample gas flow rates and for complex gaseous matrices, such as emissions from sediment samples. SSID provides simplified methodological development, as well as efficient correction for matrix induced losses and transformations of Hg species. The method could be useful for various biogeochemical studies of Hg, as well as for reliable risk assessments during, for example, waste management and soil remediation.
Knowledge of atmospheric mercury speciation is critical to understanding its fate once released from point sources. The water-soluble compounds of Hg that exist in flue gases (termed reactive gaseous mercury, RGM) are subject to far greater local removal rates than is elemental Hg vapor, but few ambient air data exist. We developed a method using refluxing mist chambers to quantify the airborne concentrations of RGM in more than 250 1-h samples under ambient conditions and summarize here the results of several RGM sampling campaigns in Tennessee and Indiana from 1992 to 1995. Measured levels of RGM were generally on the order of 50−200 pg/m3, representing about 3% of total gaseous mercury (TGM) and generally exceeding regional particulate Hg concentra tions. RGM exhibits significant correlations (p < 0.05) with temperature, solar radiation, O3, SO2, and TGM, suggesting seasonal trends similar to those of other regional air pollutants. The concentrations of RGM show reproducible diel trends, peaking during midday and decreasing sharply at night. A sharp spike in RGM was measured during a local plume impaction event in Tennessee. Concentration gradients over vegetation suggested a strong ground-level sink for RGM, and RGM concentrations decreased sharply during rain events, as expected for a water-soluble gas. The levels of RGM measured here support the hypothesis that Hg dry and wet deposition may be strongly influenced by the behavior of RGM and that elevated ecosystem exposure may be possible near major point sources of RGM compounds.
This review critically evaluates the measurement methodologies most commonly employed for the analysis of the various forms of mercury (Hg) in air. Emphasis is given to the three most common forms of mercury in air [i.e. gaseous elemental mercury (GEM, Hg 0), reactive gaseous mercury (RGM), and particle-bound mercury (Hg p)]. Moreover, we also briefly describe methods dealing with gas-phase analysis of organic mercury species (e.g., mostly methyl mercury), as they are also reported to be present in air on rare occasions. To begin with, we describe the approaches to sampling airborne mercury species and associated sample-treatment strategies. We evaluate both conventional and emerging alternative detection techniques for different mercury forms with respect to their applicability in airborne mercury analysis. We also discuss the artifacts and the biases associated with analysis of different mercury species. Finally, the review summarizes current methodological developments for the determination of mercury in air and highlights future prospects for improvements.
An improved method for the determination of gaseous divalent mercury (GDM) in ambient air using KCl coated denuders has been
developed and tested. GDM collected in the KCl coated denuders can be quantitatively desorbed at 450 °C in 10 min. After being
complete thermally reduced to Hg0 at 900 °C, all mercury released from the denuder is pre-concentrated on the analytical Au trap, and detected by cold vapor
atomic fluorescence spectrometry (CVAFS). The absolute detection limit of the method is less than 3 pg. Preliminary data of
GDM concentration in ambient air from different sampling stations show that GDM concentrations in the urban air of Göteborg
are much higher than in rural air (Rörvik and Sasetta), which indicates the anthropogenic origin of GDM.
The paper presents results of a preliminary study on mercury concentration in the air carried out in the period of October
2006 to April 2007 at sampling sites located in the cities of Gliwice and Zabrze in the region of Upper Silesia—Poland’s largest
urban and industrial agglomeration. The study comprised physical (particulate matter–gaseous phase) and chemical speciation
of gaseous mercury. Mercury concentration data related with two fractions of particulate matter: PM2.5 and PM10 are reported.
The performed measurements indicated that the average monthly concentrations of the total mercury were in the range of 4.1
to 9.1ng m−3. The highest mercury concentration was observed in winter, especially in periods of low precipitation. The investigation
of ambient mercury distribution indicated that 4.6% to 9.8% of the total mercury present in the air was bound to particulate
matter. It has been also observed that 77% of mercury in PM10 was bound to the respirable PM2.5 fraction. Chemical speciation
analysis showed that elemental mercury presented 96.1% up to 99.3% of the total gaseous mercury concentration in the air.
KCl coated denuders were employed for the measurement of divalent mercury (Hg2+) species in the air. Laboratory tests show that gaseous Hg2+ can be collected by the denuder with an average efficiency of 98% and elemental Hg will pass through it freely. Hg2+ trapped in the denuder can be quantitatively extracted by 1 mol/L HCl and analyzed by the method of SnCl2 reduction-CVAFS determination. Hg2+ concentrations of 0.04–0.15 ng m–3 corresponding to about 2–9% of the total gaseous mercury in the ambient air were determined at several sampling locations.
A model has been developed describing the mass transport and chemistry of different forms of mercury in the atmosphere (the CAM model). 48-hour simulations of an air parcel containing a fog have been used to examine the influence of a number of chemical parameters on dissolved divalent mercury, Hg(II), in fog droplets. Representation of chlorine chemistry was found to be very important for modelling of mercury species, as mercury-chloride complexes dominate the dissolved Hg(II) fraction in competition with the reactive Hg(II)S(IV) complexes. If the pH is increased, the importance of HgCl2 will decrease in favour of Hg(II)S(IV) complexes which, in turn, will lead to lowered concentrations of dissolved Hg(II), due to an enhanced production of volatile Hg0 via reduction of HgSO3 At low SO2 concentration (0.5 < SO2 < 10 ppb) dissolved mercury is strongly inversely dependent on the gas phase SO2 concentration. The ozone concentration is almost linearly related to the dissolved Hg(II) content. Total mercury content (dissolved plus adsorbed Hg(II)) is strongly correlated to soot concentration. At high soot concentrations all Hg(II) is expected to be found in the adsorbed form.
Measurements of total gaseous mercury have been made over a period of 1 yr using a cold vapour atomic fluorescence absorption technique at Harwell, a rural site in central southern England. The mean concentration was 1.68 ng m−3, with a maximum hourly mean concentration of 20.5 ng m−3 and a minimum hourly mean concentration of 0.26 ng m−3. Gaseous mercury concentrations are not greatly different from those measured at a remote rural site in Ireland, nor other measurements in Europe. The data from Harwell show greater variability than those from more remote sites but indicate a “background” of approximately 1.5 ng m−3, which is consistent with these other data. The diurnal variability of gaseous mercury at this site suggests a surface source, estimated to be of the order of 15 ng m−2 day. Two fossil-fuel combustion plants were located in the same 30° wind sector but no clear effect of these sources on gaseous mercury concentrations could be established, using sulphur dioxide as a tracer in combination with meteorological data.
There are few reliable data on the speciation of Hg in ambient air, although this information is critical to understanding the fate of Hg once released from point sources. The water soluble species of Hg that are thought to exist in flue gases would be subject to far greater local removal rates than is elemental Hg vapor, but methods are lacking to quantify this species. We developed a method using refluxing mist chambers (MC) to measure the airborne concentrations of reactive gaseous mercury (RGM) in short-term samples under ambient conditions, and have simulated the atmospheric transport and fate of anthropogenic mercury emissions over the contiguous United States. The MC method exhibits an effective detection limit of 0.02 ng/m3 and a precision for ambient concentration levels of ±20–30%. The average RGM concentrations measured with our method at sites in Tennessee (TN) and Indiana (IN) were ∼0.06 and ∼0.10 ng/m3, respectively. These averages represent about 3% of total gaseous mercury (TGM), and RGM generally exceeds regional particulate Hg. The 24-h simulated RGM concentration averages in the modeling grid cells representing TN and IN are 0.05 and 0.098 ng/m3, respectively, in good agreement with the data. These concentrations are high enough to suggest that RGM can play an important role in both wet and dry deposition on a regional scale.
This paper presents a broad overview and synthesis of current knowledge and understanding pertaining to all major aspects of mercury in the atmosphere. The significant physical, chemical, and toxicological properties of this element and its environmentally relebant species encountered in the atmosphere are examined. Atmospheric pathways and processes considered herein include anthropogenic as well as natural sources of Hg emissions to the atmosphere, aerial transport and dispersion (including spatial and temporal variability), atmospheric transformations (both physical and chemical types), wet and dry removal/deposition processes to Earth's surface. In addition, inter-compartmental (air-water/soil/vegetation) transfer and biogeochemical cycling of mercury are considered and discussed. The section on numerical modelling deals with atmospheric transport models as well as process-oriented models. Important gaps in our current knowledge of mercury in the atmospheric environment are identified, and suggestions for future areas of research are offered.
Mercury concentrations in wet deposition to a coastal and an inland site within the Chesapeake Bay watershed ranged from less than 10 pM to around 400 pM. Most concentrations were, however, below 150 pM. Speciation measurements of precipitation at the Chesapeake Biological Laboratory (CBL) (average total Hg 88 pM) show that 15% of the total Hg is reactive with methylmercury less than 0.5%, on average. Atmospheric particulate Hg measurements at the CBL site averaged 18 pgm−3, with somewhat higher winter concentrations. There is no strong indication of gaseous ionic Hg species in the Chesapeake Bay atmosphere, in contrast to what has been found elsewhere. Mercury in rain exhibited scavenging-type characteristics with the highest concentrations being found for the smaller rain events. However, a comparison of the ratio of Hg to other constituents in particulate with that of precipitation indicates that other processes besides particulate scavenging are contributing Hg to wet deposition. Thus, atmospheric oxidation of elemental mercury during rain formation and during atmospheric transport must be occurring.
Atmospheric sources are significant in the cycling of Hg in the biosphere, but there are few reliable data on air/surface exchange of Hg in terrestrial systems. We developed a tower-based micrometeorological gradient method for measuring gas-phase Hg° fluxes over soils and vegetation. We describe here results of the modified Bowen ratio approach from three separate flux sampling campaigns: over a mature deciduous forest at the Walker Branch Watershed in Tennessee, over a young pine plantation in Tennessee, and over the boreal forest floor at the Lake Gårdsjön watershed in Sweden. Our data show that Hg° exchange over these surfaces is bidirectional, but is primarily characterized by emissions from plants and soil. Dry deposition (foliar uptake) is less frequent, of generally lower magnitude, and may be enhanced by surface wetness. We measured emissions over tree canopies in Tennessee in the range of ∼ 10–300 ng m−2 h−1, and over the boreal forest floor in Sweden of ∼ 1–4 ng m−2 h−1. Fluxes were influenced by temperature, solar radiation, and atmospheric turbulence. The ability of trees to emit Hg° from soil pools has now been established. Others have proposed a significant biotic re-emission of Hg° from the oceans, and our data provide the first direct evidence of a similar process in terrestrial systems. These data have been combined with results from chamber studies to estimate the overall flux of gas-phase Hg° between the atmosphere and terrestrial systems. Transpiration of Hg° represents a previously unmeasured mobilization of Hg from the continents to the troposphere. Including this new source term could increase current estimates of so-called natural emissions by over 100%.
The atmospheric pathway of the global mercury cycle is known to be the primary source of mercury contamination to most threatened aquatic ecosystems. Current efforts toward numerical modeling of atmospheric mercury are hindered by an incomplete understanding of emissions, atmospheric transformations, and deposition processes. While much effort has been made to quantify the total mass flux of mercury to the atmosphere from various natural and anthropogenic sources, discrimination of the chemical and physical forms of these emissions is just beginning in response to early modeling exercises showing this discrimination to be critical for accurate modeling estimates of the sources responsible for observed mercury deposition. A similar discrimination of ambient concentrations of mercury throughout the atmosphere is needed in order to develop a clear understanding of atmospheric transformation processes, both chemical and physical, which govern the length scale of atmospheric mercury transport and patterns of its deposition in both wet and dry processes. In this paper, current atmospheric mercury modeling techniques and the information obtained from them are described. A strategy for future field research and numerical model development is proposed which is intended to allow a confident identification of the sources of atmospheric mercury responsible for observed contamination of aquatic ecosystems.
Yhteenveto: Elohopea Suomen metsäjärvissä ja tekoaltaissa: ihmisen vaikutus kuormitukseen ja pitoisuuksiin kaloissa.
Tropospheric concentrations of formic and acetic acids in the gas, the aerosol, and the rainwater phases were determined in samples collected 1-2 m above ground level at an open field site in eastern Virginia. These acids were found to occur principally (98 percent or above) in the gas phase, with a marked annual seasonality, averaging 1890 ppt for formate and 1310 ppt for acetate during the growing season, as compared to 695 ppt and 700 ppt, respectively, over the nongrowing season. The data support the hypothesis that biogenic emissions from vegatation are important sources of atmospheric formic and acetic acid during the local growing season. The same time trends were observed for precipitation, although with less defined seasonality. The relative increase of the acetic acid/formic acid ratio during the nongrowing season points to the dominance of anthropogenic inputs of acetic acid from motor vehicles and biomass combustion in the wintertime.
The solubility of mercury vapor in water has been measured by means of atomic absorption spectrophotometry over the temperature range of 5–60°C under atmospheric pressure. The aqueous solubility obeys Henry’s law at each temperature. The solubilities and the Henry coefficients are reported. From the solubility data, the heat of the solution of mercury vapor in water is found to be −5.3 kcal/mol. The relationship between the Henry coefficient, k, and the solution temperature, T, is expressed by logk=−1078×1⁄T+6.250. From this equation, the solubilities at 70–100°C are estimated. The solubility of the mercury vapor in sea water has also been measured over the temperature range of 5–30°C. A salting-out effect on the solubility is observed. The practical application of the aqueous solubility of the mercury vapor is discussed from the analytical point of view.
Relative consumptions of aqueous Hg0 and S(IV) due to reactions with O3 have been used to estimate the rate constant for the reaction of Hg0 and O3. Ratios ranging from <0.1 to >10 were measured in the pH range 4.5–9.5. The results were interpreted in terms of a second-order reaction of Hg0 and O3 with a rate constant k = (4.7±2.2) × 107 M−1s−1 which is independent of pH and temperature. Steady-state concentrations of dissolved inorganic mercury in atmospheric waters (rain and clouds) have been estimated using the rate constant determined in this work and previously reported rate constants for the reduction of Hg2+ by S(IV). At gas-phase concentrations of SO2>0.5 ppb, concentrations of dissolved inorganic mercury in the range 1–25 pM (0.2–5 ngℓ−1) are predicted at different pH and gas-phase concentrations of O3, which agrees reasonably well with measured concentrations. At lower SO2 concentration, the calculated values are unreasonably high, which indicates that other reducing processes may be of importance under these conditions.
During the last decade a new pattern of Hg pollution has been discerned, mostly in Scandinavia and North America. Fish from low productive lakes, even in remote areas, have been found to have a high Hg content. This pollution problem cannot be connected to single Hg discharges but is due to more widespread air pollution and long-range transport of pollutants. A large number of waters are affected and the problem is of a regional character. The national limits for Hg in fish are exceeded in a large number of lakes. In Sweden alone, it has been estimated that the total number of lakes exceeding the blacklisting limit of 1 mg Hg kg-1 in 1-kg pike is about 10 000.
A technique was developed to measure inorganic Cl gases in the marine boundary layer. The inlet inertially removed coarse aerosol (>1-mum diameter), and an in-line filter removed fine aerosol. A trace gas concentrator positioned downstream incorporated an acidic mist chamber which sampled HCI* (including HCl, NOCl, ClNO2, and ClNO3), followed by an alkaline mist chamber which sampled Cl2* (including Cl2 and a portion of HOCl). Mist solutions were analyzed by ion chromatography. Estimated detection limits for HCl* and Cl2* were 39 and 13 pptv, respectively. Standard additions of calibration gases from permeation sources to ambient air were recovered quantitatively within source uncertainties. The sampler appears to discriminate against organic Cl gases. HCl* in coastal air near Miami varied from <39 to 268 pptv with lower mixing ratios at night. Ambient Cl2* Varied from <13 to 127 pptv with highest mixing ratios before dawn.
We studied the partitioning of mercury (Hg) among air, water, sediments and fish at Little Rock Lake, a clear water seepage lake in north-central Wisconsin. The lake was divided with a sea curtain into two basins, one acidified with sulfuric acid to pH 5.6 for two years and the other an untreated reference site (mean pH 6.1), to document the effects of acidification. Trace-metal-free protocols were used to measure Hg at the picomolar level in air and water. Total gaseous Hg in air samples averaged 2.0 ng/m3. Total Hg in unfiltered water samples collected in 1986 after the fall overturn averaged about 1 ng/L in the acidified and reference basins. Mercury in surficial sediments was strongly correlated with volatile matter content and ranged from 10 to about 170 ng/g (dry weight) in both basins. Total Hg concentrations in whole, calendar age-1 yellow perch (Perca flavescens), sampled after one year of residence in the lake, averaged 114 ng/g (fresh weight) in the reference basin and 135 ng/g in the acidified basin – a highly significant (p < 0.01) difference. The mean whole-body burden (quantity) of Hg in age-1 perch did not differ between basins after the first year, but was significantly greater in the treatment basin than in the reference basin after the second year of acidification. Differences between the two basins in the bioaccumulation of Hg were attributed to internal (within-lake) processes that influence the bioavailability of the metal. An initial Hg budget for the treatment basin of Little Rock Lake showed that atmospheric deposition and sedimentary remobilization of Hg are potentially important processes influencing its biogeochemical cycling and uptake by fish.
Theoretical calculations and experimental work, mainly consisting of bubbling ambient air through different synthetic solutions
and natural waters and also bubbling Hg- and O3-free air through precipitation samples, have given some new information. The oxidation process of Hgo by means of O3 in natural waters and in synthetic solutions has been clarified. The primary products are water soluble Hg-compounds which
are reduced by SnCl2. Subsequently volatile or nonvolatile Hg-species may be formed. These are not reduced by SnCl2. Further it has been shown that in precipitation those Hg-forms, which are not reducible with SnCl2 consist of non volatile species only. The dominant one seems to be highly dispersed and easily sorbed on to solid surfaces.
It is reducible with NaBH4. Besides this there is another one consisting of larger particles. Their core contains some Hg which can be released as Hgo by a high temperature thermal process. Species with the same properties have also been observed in ambient air but in very
low concentrations.
Profiles of total mercury (Hg) concentrations in sediments were examined in 11 lakes in north-central Wisconsin having a broad range of pH (5.1 to 7.8) and alkalinity (–12 to 769 eq/L). The sediments, which were hydrous and flocculent, were collected at or near the area of maximum depth in each lake with a diver-operated sampler that permittedin situ sectioning of a 1-m core. Mercury concentrations were greatest in the top 15 cm of the cores and were much lower in the deeper strata. The Hg content in the most enriched stratum of individual cores ranged from 0.09 to 0.24 g/g dry weight, whereas concentrations in deep, precolonial strata ranged from 0.04 to 0.07 g/g. Sediment enrichment factors varied from 0.8 to 2.8 and were not correlated with lake pH. The increase in the Hg content of recent sediments was attributed to increased atmospheric deposition of the metal. Eight of the 11 systems studied were low-alkalinity lakes that presumably received most (90%) of their hydrologic input from precipitation falling directly onto the lake surface. Thus, the sedimentary Hg in these lakes seems more likely linked to direct atmospheric deposition onto the lake surfaces than to influxes from the watershed. The data imply that a potentially significant fraction of the high Hg burdens measured in game fish in certain lakes in north-central Wisconsin originated from atmospheric sources.
HNO3 is present in air in the gas as well as the particle phase. The gas phase is difficult to sample due to its extremely high affinity for most materials. When particulate nitrate is removed by filtration it may release gaseous HNO3. These difficulties can be overcome by first removing the gas phase in a Na2CO3-coated denuder and then by collecting the particle phase on a Na2CO3-impregnated filter. After sampling they are separately leached with water and the nitrate content is determined by ion chromatography. The detection limit for 24-h sampling is about 0.5 nmole m−3 (0.01 ppb) for HNO3 and 3 nmole m−3 for particulate NO−3. The sampling equipment is cheap and a relatively cheap ion chromatograph can be constructed according to the description in this article. When ion chromatography is used the ambient SO2 and particulate SO2−4 concentrations will also be obtained.
Alkylmercury compounds were preconcentrated from air on a Carbotrap (graphitized carbon black) column at room temperature. The species were then transferred by thermal desorption to a U-tube chromatographic column packed with 15% OV-3 on Chromosorb WAW-DMSC, held at −196°C in liquid nitrogen. The compounds were clearly separated and eluted in order of increasing polarity using a simple, ramped heating step to 180°C over 20 min. After thermal decomposition of the eluant, the resultant mercury vapour was detected by cold-vapour atomic fluorescence spectrometry. The detection limits (as Hg) for the system were approximately 0.3 pg for mercury and dimethylmercury, 0.4 pg for diethylmercury, and 2.0 pg for methylmercury chloride. A study of the Long Island Sound atmosphere showed Hg0 to account for 95–100% of the total mercury present, with the remainder being monomethylmercury.
The aqueous phase oxidation of elemental mercury by ozone has been investigated in the laboratory using a quartz glass reactor with gas phase concentrations of 400–1800ng m−3 and 70–200 ppb for Hg(0) and O3, respectively. The absorption of Hg in the water phase was increased by three orders of magnitude with O3 present. If the oxidation were to proceed with the same speed in liquid water in contact with the atmosphere,conversion rales of 1–4% h−1 would be implied. Experiments using ambient urban air with 2–6 ng Hg m−3 confirm the process at elevated O3 concentrations. At ambient O3 concentrations competitive reactions become important, e.g. O3 consumption by SO2, hydrocarbons etc., and even some reduction of Hg2+ could occur. The atmospheric oxidation of Hg(0) by O3 in water is thus considered important at high O3 levels in regionally polluted or remote areas.
This article describes an improved technique for making in situ measurements of gaseous tropospheric formaldehyde (CH2O). The new technique is based on nebulization/reflux principles that have proved very effective in quantitatively scrubbing water soluble trace gases (e.g. CH2O) into aqueous mediums, which are subsequently analyzed. Atmospheric formaldehyde extractions and analyses have been performed with the nebulization/reflux concentrator using an acidified dinitrophenylhydrazine solution that indicate that quantitative analysis of CH2O at global background levels (∼ 0.1 ppbv) is feasible with 20-min extractions. Analysis of CH2O, once concentrated, is accomplished using high performance liquid chromatography (HPLC) with ultraviolet photometric detection. The CH2O-hydrazone derivative, produced by the reaction of 2,4-dinitrophenylhydrazine in H2SO4 acidified aqueous solution, is detected as CH2O.
A new concentration technique for the extraction and enrichment of water-soluble atmospheric trace gases has been developed. The gas scrubbing technique efficiently extracts soluble gases from a large volume flow rate of air sample into a small volume of refluxed trapping solution. The gas scrubber utilizes a small nebulizing nozzle that mixes the incoming air with an aqueous extracting solution to form an air/droplet mist. The mist provides excellent interfacial surface areas for mass transfer. The resulting mist sprays upward through the reaction chamber until it impinges upon a hydrophobic membrane that virtually blocks the passage of droplets but offers little resistance to the existing gas flow. Droplets containing the scrubbed gases coalesce on the membrane and drip back into the reservoir for further refluxing. After a suitable concentration period, the extracting solution containing the analyte can be withdrawn for analysis. The nebulization-reflex concentration technique is more efficient (maximum flow of gas through the minimum volume of extractant) than conventional bubbler/impinger gas extraction techniques and is offered as an alternative method.
During June 1986, eight systems for measuring vapor phase and four for measuring particulate phase concentrations of formic acid (HCOOH) and acetic acid (CH3COOH) were intercompared in central Virginia. HCOOH and CH3COOH vapors were sampled by condensate, mist, Chromosorb 103 GC resin, NaOH-coated annular denuders, NaOH-impregnated quartz filters, K2CO3 and NaCO3-impregnated cellulose filters, and Nylasorb membranes. Atmospheric aerosol was collected on Teflon and Nuclepore filters using both hi-vol and lo-vol systems to measure particulate phase concentrations. Performances of the mist chamber and K2CO3-impregnated filter techniques were evaluated using zero air and ambient air spiked with HCOOH(g) and CH3COOH(g), and formaldehyde from permeation sources. The advantages and drawbacks of these methods are reported and discussed.
A series of laboratory and field measurements was performed to evaluate the mist chamber technique for determining tropospheric HNO3 concentrations. Both the mist chamber and standard Nylon filter techniques exhibit high collection efficiency and excellent agreement measuring HNO3 vapors from a permeation source. When simultaneously sampling ambient air in eastern Virginia, the Nylon filter measured an average of 70 percent higher HNO3 concentration than the mist chamber technique. The results indicate that O3 causes a low-level positive artifact interference in HNO3 measurements performed with the filter technique. This O3-induced error is small, however, compared to the large difference between atmospheric HNO3 concentrations determined with the two techniques. It is hypothesized that unidentified (organic?) nitrogen species in the atmosphere react for form NO3(-) on the filter and this phenomenon may interfere with Nylon filter measurements of HNO3 vapor. These potential interferences did not appear to affect measurements of HNO3 with the mist chamber method.
A new method for measuring tropospheric sulfur dioxide concentrations is proposed which is based on the mist chamber sampling method. At the present stage of development, the detection limit of the method is approximately 20 parts per trillion for a 45-min sampling time, with lower concentrations detectable with lower precision. The overall reproducibility of the method (+/-95 percent confidence intervals) is estimated at +/-10 percent. The technique is relatively simple, inexpensive, and lightweight, making it ideally suited for numerous field applications in atmospheric chemistry and biogeochemical studies from both ground-based and airborne platforms.
To test whether any photochemical process is occurring within the chamber, several tests were carded out in which the chamber was covered with aluminum foil during sampling. Paired sequential samples, with & without foil, showed no statistically-significant difference in concentrations of Hg(II)
- Photochemical
Photochemical effects. To test whether any photochemical process is occurring within the chamber, several tests were carded out in which the chamber was covered with aluminum foil during sampling. Paired sequential samples, with & without foil, showed no statistically-significant difference in concentrations of Hg(II).
LINDBERG either impossible or could, at the same time, remove some unknown portion of Hg(II)
- W J Stratton
W.J. STRATTON AND S. E. LINDBERG either impossible or could, at the same time, remove some unknown portion of Hg(II).
II) in excess of either artifact Hg(II) created within the mist chamber or particulate-Hg(II) extracted in the chamber, we now turn to a brief discussion of the assembled data At our study sites, the total gaseous Hg (designated as Hg ~ was generally in the range of 2 to 6 ng
- N S Bloom
- W F Fitzgerald
SUMMARY OBSERVATIONS ABOUT ATMOSPHERIC Hg SPECIES. Having tentatively concluded that we are measuring Hg(II) in excess of either artifact Hg(II) created within the mist chamber or particulate-Hg(II) extracted in the chamber, we now turn to a brief discussion of the assembled data. At our study sites, the total gaseous Hg (designated as Hg ~ was generally in the range of 2 to 6 ng/m 3, with a tendency for References Bloom, N.S. and Fitzgerald, W.F.: 1987, Anal. chim, Acta. 208, 151. Bloom, N.C.: 1992, paper presented at the International Conference on Mercury as a Global Pollutant, Monterey, CA, June 1992. Brosset, C. and Lord, E.:1991, Water, Air, and Soil Pollution, 56, 493. Cofer, W. R., and Edahl, R. A., :1986, Atm. Environ, 20, 979-984.
C.: 1992, paper presented at the International Conference on Mercury as a Global Pollutant
- N Bloom
Model Studies on the Atmospheric Transport and Deposition of Mercury
- G Petersen
- D Eppel
- H Grassl
- A Iverfeldt
- P K Misra
- R Bloxam
- S Wong
- Wh Schroeder
- E Voldner
- J Pacyna
International Conference on Mercury as an Environmental Pollutant, Abstract Collection
- C J Watras
Mercury Atmospheric Processes: A Synthesis Report
- R H Osa
Water Air and Soil Pollution, this volume
- E M Prestbo
- N S Bloom