Gaseous Elemental Mercury Concentrations Research Articles

Spatial and temporal distribution of gaseous elemental mercury in Chongqing, China

In order to investigate the spatial and temporal variability of atmospheric mercury (Hg) in Chongqing, China, gaseous elemental mercury (GEM) was measured from August 2006 to September 2007, using Lumex multifunctional mercury analyzer RA-915(+) (Lumex Ltd., Russia). The mean GEM concentration was 6.74 +/- 0.37 ng m(-3) in Chongqing, much higher than the accepted global background values (1.5-2 ng m(-3)). The GEM concentrations were different in different function areas. GEM in transport, industrial and commercial areas were 7.07 +/- 1.04, 7.05 +/- 0.96 and 6.71 +/- 1.10 ng m(-3), respectively, while GEM was 6.14 +/- 1.30 and 4.32 +/- 1.04 in the educational/recreational and nature conservation areas, suggesting that Hg emissions from mobile vehicles and industrial sources (specially coal combustion) were the most important contributors to atmospheric Hg in Chongqing. Mean Hg concentrations also had monthly variations with highest in November (8.24 +/- 0.50 ng m(-3)) and lowest values in August (5.36 +/- 0.70 ng m(-3)). Additionally, the diurnal variation of GEM concentrations was dependent on the local/regional atmospheric conditions. At Jinyun Mountain site (natural conservation area), hourly GEM concentrations had much higher values in daytime than at night. At Power Plant site, however, the hourly GEM concentrations were lower in daytime than at night. GEM concentrations in the air were correlated significantly with meteorological parameters except for barometric pressure.

Airborne mercury pollution from a large oil spill accident on the west coast of Korea

Atmospheric mercury pollution was recognized after a large oil spill on the west coast of Korea on 7 December 2007. In this study, the concentrations of gaseous elemental mercury (GEM: Hg 0) in air were measured both shortly after the oil spill (∼100 h) and 1 month after the accident near the accident site. When the Hg concentration levels were compared between two seashore sites and two parallel sites offshore, the values tend to decrease further offshore. The unusual rise in Hg concentration levels observed on the seashore area shortly after the accident (mean of 16.4 ± 9.85 ng m −3) dropped dramatically after 1 month with active cleanup activities (2.99 ± 1.40 ng m −3). Because of the connection between crude oil and Hg (one of the major impurities), the unusual rise in the atmospheric Hg after the oil spill can be explained by the active evasion of Hg from the spilled crude oil. Although Hg levels determined a few days after the accident did not exceed the reference exposure limits (REL) proposed by several agencies, the early build-up of elemental mercury level due to the oil spill might have exerted certain impacts on the surrounding environments.

Reactive and particulate mercury in the Asian marine boundary layer

The variability of atmospheric mercury in elemental, reactive, and particulate forms has been studied at a remote site (Cape Hedo Observatory, CHO) at Okinawa Island (Japan) March 23 to May 2, 2004, downwind of the major Asian source regions. Under prevailing meteorological conditions, episodes of higher levels of atmospheric mercury and other atmospheric species are observed at CHO. The mean (±1 σ) concentrations of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particulate-bound mercury (PHg) are 2.04 ± 0.38 ng m −3, 4.5 ± 5.4 pg m −3 and 3.0 ± 2.5 pg m −3, respectively. In Asian outflow the combined contribution of RGM and PHg constitutes less than 1% of the GEM in the boundary layer, which indicates that most mercury export in the marine boundary layer is due to the GEM form, and direct outflow of RGM and PHg is very low. While the data from Okinawa suggest minimal export of RGM and PHg, this does not preclude greater export of these species at higher elevations. Based on the correlations of PHg and submicron aerosol mass (SAM), we found a ΔPHg/ΔSAM ratio of 0.20 μg g −1 ( R = 0.58, p < 0.01), which we believe to be characteristic of East Asian industrial aerosols during outflow. A diurnal variation is observed in RGM with a peak near noon. Using a rate constant of 9 × 10 −14 cm 3 molecule −1 s −1 for the OH oxidation rate (Sommar, J., Gardfeldt, K., Stromberg, D., Feng, X., 2001. A kinetic study of the gas phase reaction between the hydroxyl radical and atomic mercury. Atmospheric Environment 35, 3049–3054; Pal, B., Ariya, P.A., 2004a. Gas-phase HO center dot-initiated reactions of elemental mercury: kinetics, product studies, and atmospheric implications. Environmental Science and Technology 38 (21), 5555–5566.) and a typical OH concentration of 1–5 × 10 6 cm −3 would result in RGM production rates of 0.6–3.0 pg m −3 h −1. Although OH may not be the sole oxidant, this is consistent with the observed change in concentration during daytime of 1.4 ± 1.5 pg m −3 h −1. A significant correlation is found between GEM and CO; GEM and SAM; and PHg and SAM. Lower ΔSAM/ΔCO and ΔGEM/ΔCO are observed for transport events with rainfall and for air parcels remaining in the mixed layer. Back trajectory analysis along with the correlation study suggests that the air from China has a higher GEM concentration compared to the air coming from southern Japan.

Fumarole compositions and mercury emissions from the Tatun Volcanic Field, Taiwan: Results from multi-component gas analyser, portable mercury spectrometer and direct sampling techniques

Gas emissions from Tatun volcanic group, northern Taiwan, were studied for the first time using a multi-component gas analyser system (Multi-GAS) in combination with Giggenbach flask methods at fumaroles and mud pools at Da-you-keng (DYK) and Geng-tze-ping (GZP). CO 2/S molar ratios observed at DYK ranged from 3–17, similar ratios were observed using a Multi-GAS sensor box of 8–16. SO 2 at GZP was low, higher concentrations were observed at DYK where SO 2/H 2S ratios were close to 1 for both methods. A lower CO 2/H 2S ratio was measured via Giggenbach flask sampling (7.2) than was found in the plume using the gas sensor at GZP (9.2). This may reflect rapid oxidation of H 2S as it mixes with background air. Gaseous elemental mercury (GEM) levels were observed in the fumarole gases using a portable mercury spectrometer. These are the first such measurements of mercury at Tatun. Mean GEM concentrations in the fumarole plumes were ∼ 20 ng m − 3 , with much higher concentrations observed close to the ground (mean [GEM] 130 and 290 ng m − 3 at DYK and GZP, respectively). The GEM in the fumarole plume was elevated above concentrations in industrial/urban air in northern Taiwan and the increase in GEM observed when the instrument was lowered suggests high levels of mercury are present in the surrounding ground surface. The GEM/CO 2 (10 − 8 ) and GEM/S (10 − 6 ) ratios observed in the fumarole gases were comparable to those observed at other low-temperature fumaroles. Combining the Hg/CO 2 ratio with a previous CO 2 flux value for the area, the annual GEM flux from the Tatun field is estimated as 5–50 kg/year.

Modeling Dynamic Exchange of Gaseous Elemental Mercury at Polar Sunrise

At polar sunrise, gaseous elemental mercury (GEM) undergoes an exceptional dynamic exchange in the air and at the snow surface during which GEM can be rapidly removed from the atmosphere (the so-called atmospheric mercury depletion events (AMDEs)) as well as re-emitted from the snow within a few hours to days in the Polar Regions. Although high concentrations of total mercury in snow following AMDEs is well documented, there is very little data available on the redox transformation processes of mercury in the snow and the fluxes of mercury at the air/snow interface. Therefore, the net gain of mercury in the Polar Regions as a result of AMDEs is still an open question. We developed a new version of the global mercury model, GRAHM, which includes for the first time bidirectional surface exchange of GEM in Polar Regions in spring and summer by developing schemes for mercury halogen oxidation, deposition, and re-emission. Also for the first time, GOME satellite data-derived boundary layer concentrations of BrO have been used in a global mercury model for representation of halogen mercury chemistry. Comparison of model simulated and measured atmospheric concentrations of GEM at Alert, Canada, for 3 years (2002-2004) shows the model's capability in simulating the rapid cycling of mercury during and after AMDEs. Brooks et al. (1) measured mercury deposition, reemission, and net surface gain fluxes of mercury at Barrow, AK, during an intensive measurement campaign for a 2 week period in spring (March 25 to April 7, 2003). They reported 1.7, 1.0 +/- 0.2, and 0.7 +/- 0.2 microg m(-2) deposition, re-emission, and net surface gain, respectively. Using the optimal configuration of the model, we estimated 1.8 microg m(-2) deposition, 1.0 microg m(-2) re-emission, and 0.8 microg m(-2) net surface gain of mercury for the same time period at Barrow. The estimated net annual accumulation of mercury within the Arctic Circle north of 66.5 degrees is approximately 174 t with +/-7 t of interannual variability for 2002-2004 using the optimal configuration. We estimated the uncertainty of the model results to the Hg/Br reaction rate coefficient to be approximately 6%. Springtime is clearly demonstrated as the most active period of mercury exchanges and net surface gain (approximately 46% of annual accumulation) in the Arctic.

A synthesis of atmospheric mercury depletion event chemistry in the atmosphere and snow

Abstract. It was discovered in 1995 that, during the spring time, unexpectedly low concentrations of gaseous elemental mercury (GEM) occurred in the Arctic air. This was surprising for a pollutant known to have a long residence time in the atmosphere; however conditions appeared to exist in the Arctic that promoted this depletion of mercury (Hg). This phenomenon is termed atmospheric mercury depletion events (AMDEs) and its discovery has revolutionized our understanding of the cycling of Hg in Polar Regions while stimulating a significant amount of research to understand its impact to this fragile ecosystem. Shortly after the discovery was made in Canada, AMDEs were confirmed to occur throughout the Arctic, sub-Artic and Antarctic coasts. It is now known that, through a series of photochemically initiated reactions involving halogens, GEM is converted to a more reactive species and is subsequently associated to particles in the air and/or deposited to the polar environment. AMDEs are a means by which Hg is transferred from the atmosphere to the environment that was previously unknown. In this article we review Hg research taken place in Polar Regions pertaining to AMDEs, the methods used to collect Hg in different environmental media, research results of the current understanding of AMDEs from field, laboratory and modeling work, how Hg cycles around the environment after AMDEs, gaps in our current knowledge and the future impacts that AMDEs may have on polar environments. The research presented has shown that while considerable improvements in methodology to measure Hg have been made but the main limitation remains knowing the speciation of Hg in the various media. The processes that drive AMDEs and how they occur are discussed. As well, the role that the snow pack and the sea ice play in the cycling of Hg is presented. It has been found that deposition of Hg from AMDEs occurs at marine coasts and not far inland and that a fraction of the deposited Hg does not remain in the same form in the snow. Kinetic studies undertaken have demonstrated that bromine is the major oxidant depleting Hg in the atmosphere. Modeling results demonstrate that there is a significant deposition of Hg to Polar Regions as a result of AMDEs. Models have also shown that Hg is readily transported to the Arctic from source regions, at times during springtime when this environment is actively transforming Hg from the atmosphere to the snow and ice surfaces. The presence of significant amounts of methyl Hg in snow in the Arctic surrounding AMDEs is important because this species is the link between the environment and impacts to wildlife and humans. Further, much work on methylation and demethylation processes has occurred but these processes are not yet fully understood. Recent changes in the climate and sea ice cover in Polar Regions are likely to have strong effects on the cycling of Hg in this environment; however more research is needed to understand Hg processes in order to formulate meaningful predictions of these changes.

A comparison of speciated atmospheric mercury at an urban center and an upwind rural location

Gaseous elemental mercury (GEM), particulate mercury (PHg) and reactive gaseous mercury (RGM) were measured every other hour at a rural location in south central Wisconsin (Devil's Lake State Park, WI, USA) between April 2003 and March 2004, and at a predominantly downwind urban site in southeastern Wisconsin (Milwaukee, WI, USA) between June 2004 and May 2005. Annual averages of GEM, PHg, and RGM at the urban site were statistically higher than those measured at the rural site. Pollution roses of GEM and reactive mercury (RM; sum of PHg and RGM) at the rural and urban sites revealed the influences of point source emissions in surrounding counties that were consistent with the US EPA 1999 National Emission Inventory and the 2003-2005 US EPA Toxics Release Inventory. Source-receptor relationships at both sites were studied by quantifying the impacts of point sources on mercury concentrations. Time series of GEM, PHg, and RGM concentrations were sorted into two categories; time periods dominated by impacts from point sources, and time periods dominated by mercury from non-point sources. The analysis revealed average point source contributions to GEM, PHg, and RGM concentration measurements to be significant over the year long studies. At the rural site, contributions to annual average concentrations were: GEM (2%; 0.04 ng m(-3)); and, RM (48%; 5.7 pg m(-3)). At the urban site, contributions to annual average concentrations were: GEM (33%; 0.81 ng m(-3)); and, RM (64%; 13.8 pg m(-3)).

Atmospheric mercury near Salmon Falls Creek Reservoir in southern Idaho

Abstract Gaseous elemental mercury (GEM) and reactive gaseous mercury (RGM) were measured over 2-week seasonal field campaigns near Salmon Falls Creek Reservoir in south-central Idaho from the summer of 2005 through the fall of 2006 and over the entire summer of 2006 using automated Tekran Hg analyzers. GEM, RGM, and particulate Hg (HgP) were also measured at a secondary site 90 km to the west in southwestern Idaho during the summer of 2006. The study was performed to characterize Hg air concentrations in the southern Idaho area for the first time, estimate Hg dry deposition rates, and investigate the source of observed elevated concentrations. High seasonal variability was observed with the highest GEM (1.91 ± 0.9 ng m −3 ) and RGM (8.1 ± 5.6 pg m −3 ) concentrations occurring in the summer and lower values in the winter (1.32 ± 0.3 ng m −3 , 3.2 ± 2.9 pg m −3 for GEM, RGM, respectively). The summer-average HgP concentrations were generally below detection limit (0.6 ± 1 pg m −3 ). Seasonally averaged deposition velocities calculated using a resistance model were 0.034 ± 0.032, 0.043 ± 0.040, 0.00084 ± 0.0017 and 0.00036 ± 0.0011 cm s −1 for GEM (spring, summer, fall and winter, respectively) and 0.50 ± 0.39, 0.40 ± 0.31, 0.51 ± 0.43 and 0.76 ± 0.57 cm s −1 for RGM. The total annual RGM + GEM dry deposition estimate was calculated to be 11.9 ± 3.3 μg m −2 , or about 2/3 of the total (wet + dry) deposition estimate for the area. Periodic elevated short-term GEM (2.2–12 ng m −3 ) and RGM (50–150 pg m −3 ) events were observed primarily during the warm seasons. Back-trajectory modeling and PSCF analysis indicate predominant source directions to the SE (western Utah, northeastern Nevada) and SW (north-central Nevada) with fewer inputs from the NW (southeastern Oregon and southwestern Idaho).

Diurnal production of gaseous mercury in the alpine snowpack before snowmelt

In March 2005, an extensive mercury study was performed just before snowmelt at Col de Porte, an alpine site close to Grenoble, France. Total mercury concentration in the snowpack ranged from 80 ± 08 to 160 ± 15 ng l−1, while reactive mercury was below detection limit (0.2 ng l−1). We observed simultaneously a production of gaseous elemental mercury (GEM) in the top layer of the snowpack and an emission flux from the snow surface to the atmosphere. Both phenomena were well correlated with solar irradiation, indicating photo‐induced reactions in the snow interstitial air (SIA). The mean daily flux of GEM from the snowpack was estimated at ∼9 ng m−2 d−1. No depletion of GEM concentrations was observed in the SIA, suggesting no occurrence of oxidation processes. The presence of liquid water in the snowpack clearly enhanced GEM production in the SIA. Laboratory flux chamber measurements enabled us to confirm that GEM production from this alpine snowpack was first driven by solar radiation (especially UVA and UVB radiation), and then by liquid water in the snowpack. Finally, a large GEM emission from the snow surface occurred during snowmelt, and we report total mercury concentrations in meltwater of about 72 ng l−1.

Sequential variation of atmospheric mercury in Tokai‐mura, seaside area of eastern central Japan

Concentrations of gaseous elemental mercury (GEM) were continuously measured from October 2005 to August 2006 in Tokai‐mura (36.27°N, 140.36°E), a small city on the Pacific side of central Japan. The concentration of atmospheric mercury in summer and autumn is higher than in winter and spring, and an 11‐month average of 1‐hour measurements is 3.78 ± 1.62 ng/m3 (n = 7551). Our results showed that changes in the GEM level in Tokai‐mura are largely determined by temperature and relative humidity, but are independent of wind speed and direction. Two contrary patterns were observed in the daily cycle of GEM concentrations: the most frequent pattern of lower concentrations at noon and a pattern of higher concentrations at noon, which was only observed in November. Our results showed that two nearby potential anthropogenic sources of mercury, a coal‐fired power plant and incineration facility, have only little effect on the gaseous elemental mercury (GEM) in Tokai‐mura based on only GEM measurements.

Atmospheric mercury over the NE Pacific during spring 2002: Gradients, residence time, upper troposphere lower stratosphere loss, and long‐range transport

Gaseous elemental mercury (GEM) was measured over the North Pacific and coastal California, Oregon and Washington in spring 2002 during the Intercontinental Transport and Chemical Transformation Experiment–2002 (ITCT2K2). Observations were made from the NOAA WP3 on 11 flights which spanned an altitude range of 0–8 km and latitudes between 35 and 55°N. GEM was determined using a Tekran 2537A mercury instrument modified for airborne use to collect and analyze samples every 2.5 min under variable ambient temperature and pressure conditions. GEM concentrations were in general at the low end of previous measurements made over continents and in fresh continental outflow over the ocean. They showed (1) a significant vertical gradient in GEM between the lower sample altitudes and the upper altitudes, with median concentrations decreasing from 1.2 to 0.5 ng m−3; (2) GEM was depleted in upper troposphere lower stratospheric air and indicated this region is a sink for GEM; (3) GEM concentrations were ∼1/2 at the surface to ∼1/4 at midaltitudes of those observed immediately downwind of Asia during ACE‐Asia, however; (4) highest GEM concentrations (∼4 ng m−3) were found in plume layers at concentrations comparable to those observed off the Asian coast in ACE‐Asia; and (5) the observed variance in GEM suggested a lifetime on the order of 100 days, which was shorter than the previously accepted nominal lifetime of 1 year.

Introduction

Observations of atmospheric mercury over the Southern Ocean and Antarctica are still limited. We performed a ship cruise from Cape Point, South Africa, to the Indian Bharati station, Prydz Bay, Antarctica (42.72°S 24.52°E to 69.41°S 76.19°E, 2015.01.18–27) and subsequently stationed the ship near the Bharati till 2015.02.19. We report relatively constant values of gaseous elemental mercury (GEM) concentration during the cruise (1.08 ± 0.08 ng/m3, n = 541) and highly variable values at the coast (0.96 ± 0.36 ng/m3, n = 1050). Meteorological parameters: relative humidity, temperature and solar radiation had almost negligible effect on GEM concentration (adjusted R2 = 0.09 in multiple linear regression model) during the ship cruise and a limited effect on GEM (adjusted R2 = 0.34) during the ship stay at Bharati. Analysis of NOAA-HYSPLIT 24-h back trajectories showed that all trajectories were extremely shallow during the ship cruise and therefore results likely were affected by the marine boundary layer rather than long-range transport. On the other hand, highly variable values of GEM near Bharati station were explained as a result of interplay of shallow and descending air masses coming from the Antarctic coast and from the terrain. These factors together with temperature dependency indicated that the coast of Antarctica acted as a temperature-driven source of GEM during the austral summer. Measurements were performed with a portable atomic absorption (CVAAS) mercury analyzer model Gardis-5. In our knowledge, this was the first time the CVAAS method was successfully applied for the background Antarctic observations.

Springtime atmospheric mercury speciation in the McMurdo, Antarctica coastal region

This paper describes springtime atmospheric mercury (Hg) speciation and snow pack mercury concentration measurements in the McMurdo/Ross Island sea ice region of Antarctica. Near-surface gaseous elemental mercury (GEM) depletions (to concentrations below our detection limit, <0.01 ng m −3), similar to those shown to occur in the springtime Arctic, were observed and reactive gaseous mercury (RGM) and fine particulate mercury (FPM) were produced in significant quantities (average 116 and 49 pg(Hg) m −3, respectively). GEM concentrations in the near-surface air were significantly enhanced during brief afternoon terrestrial snowmelt events. Snow pack total mercury was significantly elevated (40–430 ng l −1), with a maximum at the northern extent of the fast-ice (adjacent to the grease ice/freezing ocean surface), and lesser values towards the coast and on Ross Island, suggesting that, similarly again to recent Arctic results, marine halogens, released by the freezing sea surface, induce localized mercury depletion events. A possible secondary contributing source of local halogens and mercury are direct emissions from the active Ross Island volcano, Mt. Erebus.

GEM fluxes and atmospheric mercury concentrations (GEM, RGM and [formula omitted]) in the Canadian Arctic at Alert, Nunavut, Canada (February–June 2005)

Five months of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particle bound mercury ( Hg p ) concentrations as well as fluxes of GEM were measured at Alert, Nunavut, Canada above the Arctic snow pack. The study spanned February to June of 2005 to capture the effects of polar night, the transition period between night and day as well as polar day on the behaviour of mercury in the near surface atmosphere. A micrometeorological approach was used to infer the flux of GEM using a continuous two-level sampling system to measure the GEM concentration gradient. The required turbulent transfer coefficients were derived from meteorological parameters measured on site. The flux of GEM was approximately zero during atmospheric mercury depletion events (AMDEs) demonstrating that mercury is not being deposited as GEM to the snow pack. Following AMDEs, there was no evidence of a net emission of GEM. The highest depositional fluxes of GEM occurred during polar night and the largest emission occurred when the tundra was first visible, followed by significant emission and deposition fluxes during the snow melt. Fluxes continued until the snow had completely melted ( ∼ JD 170) before returning to near zero. Average concentrations of RGM ( 44.4 ± 49.8 pg m - 3 ) , Hg p ( 102.6 ± 124.9 pg m - 3 ) and GEM ( 1.0 ± 0.4 ng m - 3 ) were variable throughout the study due to the dynamic nature of atmospheric mercury during AMDEs. Increases in Hg p preceded elevated levels of RGM during AMDEs by 60 days, yielding peak levels at 694 and 344 pg m - 3 , respectively. Elevated concentrations of Hg p typically occurred when the specific humidity dropped below 0.75 g kg - 1 , winds were light ( < 3 m s - 1 ) and the air temperature dropped below - 20 ∘ C . Increased levels of RGM were also noted when the winds were light ( < 3 m s - 1 ) but when the temperature increased above - 10 ∘ C and the specific humidity was in the range of 1 and 3 g kg - 1 . As different environmental conditions were observed for the elevated concentrations of Hg p versus RGM at Alert, it suggests that the formation mechanisms for each species may be different but tied to the atmospheric temperature and water content. Total mercury (TM) levels in fresh snow measured approximately 5– 10 ng l - 1 during AMDEs and reached nearly 80 ng l - 1 outside of depletion events, suggesting that wet deposition may not be a significant removal mechanism of GEM during depletion events. An unusually high concentration of TM was measured during a non-depletion event which coincided with the transitional period where atmospheric loading of RGM exceeded levels of Hg p .

Scientific uncertainties in atmospheric mercury models II: Sensitivity analysis in the CONUS domain

In this study, we present the response of model results to different scientific treatments in an effort to quantify the uncertainties caused by the incomplete understanding of mercury science and by model assumptions in atmospheric mercury models. Two sets of sensitivity simulations were performed to assess the uncertainties using modified versions of CMAQ-Hg in a 36-km Continental United States domain. From Set 1 Experiments, it is found that the simulated mercury dry deposition is most sensitive to the gaseous elemental mercury (GEM) oxidation product assignment, and to the implemented dry deposition scheme for GEM and reactive gaseous mercury (RGM). The simulated wet deposition is sensitive to the aqueous Hg(II) sorption scheme, and to the GEM oxidation product assignment. The inclusion of natural mercury emission causes a small increase in GEM concentration but has little impact on deposition. From Set 2 Experiments, it is found that both dry and wet depositions are sensitive to mercury chemistry. Change in model mercury chemistry has a greater impact on simulated wet deposition than on dry deposition. The kinetic uncertainty of GEM oxidation by O 3 and mechanistic uncertainty of Hg(II) reduction by aqueous HO 2 pose the greatest impact. Using the upper-limit kinetics of GEM–O 3 reaction or eliminating aqueous Hg(II)–HO 2 reaction results in unreasonably high deposition and depletion of gaseous mercury in the domain. Removing GEM–OH reaction is not sufficient to balance the excessive mercury removal caused by eliminating the HO 2 mechanism. Field measurements of mercury dry deposition, better quantification of mercury air-surface exchange and further investigation of mercury redox chemistry are needed for reducing model uncertainties and for improving the performance of atmospheric mercury models.

Intercomparison study of atmospheric mercury models: 1. Comparison of models with short-term measurements

Five regional scale models with a horizontal domain covering the European continent and its surrounding seas, one hemispheric and one global scale model participated in an atmospheric mercury modelling intercomparison study. Model-predicted concentrations in ambient air were compared against mercury species observed at four monitoring stations in Central and Northern Europe and a station on the Irish west coast. The modelled concentrations of total particulate mercury (TPM) were generally consistent with the measurements at all sites. The models exhibited significant ability to simulate concentrations of gaseous elemental mercury (GEM), but some of the short-duration peaks at the Central European stations could not be consistently reproduced. Possible reasons for these discrepancies include (1) errors in the anthropogenic emissions inventory utilized; (2) coarse spatial resolution of the models; and (3) uncertainty of natural and re-emitted mercury sources. The largest discrepancies between measurements and modelled concentrations were found for reactive gaseous mercury (RGM). For these models, the uncertainty in predicting short-term (two-week episode) variations of mercury species in air can be characterized by the following overall statistics: 90% of the results for TGM are within a factor of 1.35 of the measurements; for TPM, 90% are within a factor of 2.5; and for RGM, 90% are within a factor of 10.

Socioeconomic Consequences of Mercury Use and Pollution

In the past, human activities often resulted in mercury releases to the biosphere with little consideration of undesirable consequences for the health of humans and wildlife. This paper outlines the pathways through which humans and wildlife are exposed to mercury. Fish consumption is the major route of exposure to methylmercury. Humans can also receive toxic doses of mercury through inhalation of elevated concentrations of gaseous elemental mercury. We propose that any effective strategy for reducing mercury exposures requires an examination of the complete life cycle of mercury. This paper examines the life cycle of mercury from a global perspective and then identifies several approaches to measuring the benefits of reducing mercury exposure, policy options for reducing Hg emissions, possible exposure reduction mechanisms, and issues associated with mercury risk assessment and communication for different populations.

Gaseous elemental mercury concentration in atmosphere at urban and remote sites in China

An investigation of gaseous elemental mercury concentration in atmosphere was conducted at Beijing and Guangzhou urban. Yangtze Delta regional sites and China Global Atmosphere Watch Baseline Observatory (CGAWBO) in Mt. Waliguan of remote continental area of China. High temporal resolved data were obtained using automated mercury analyzer RA-915 +. Results showed that the overall hourly mean Hg 0 concentrations in Mt. Waliguan were 1.7±1.1 ng/m 3 in summer and 0.6±0.08 ng/m 3 in winter. The concentration in Yangtze Delta regional site was 5.4±4.1 ng/m 3, which was much higher than those in Waliguan continental background area and also higher than that found in North America and Europe rural areas. In Beijing urban area the overall hourly mean Hg 0 concentrations were 8.3±3.6 ng/m 3 in winter, 6.5±5.2 ng/m 3 in spring, 4.9±3.3 ng/m 3 in summer, and 6.7±3.5 ng/m 3 in autumn, respectively, and the concentration was 13.5±7.1 ng/m 3 in Guangzhou site. The mean concentration reached the lowest value at 14:00 and the highest at 02:00 or 20:00 in all monitoring campaigns in Beijing and Guangzhou urban areas, which contrasted with the results measured in Yangtze Delta regional site and Mt. Waliguan. The features of concentration and diurnal variation of Hg 0 in Beijing and Guangzhou implied the importance of local anthropogenic sources in contributing to the high Hg 0 concentration in urban areas of China. Contrary seasonal variation patterns of Hg 0 concentration were found between urban and remote sites. In Beijing the highest Hg 0 concentration was in winter and the lowest in summer, while in Mt. Waliguan the Hg 0 concentration in summer was higher than that in winter. These indicated that different processes and factors controlled Hg 0 concentration in urban, regional and remote areas.

Measurements of GEM fluxes and atmospheric mercury concentrations (GEM, RGM and Hg p) from an agricultural field amended with biosolids in Southern Ont., Canada (October 2004–November 2004)

Five weeks of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particle bound mercury (Hg p) concentrations as well as fluxes of GEM were measured at Maryhill, Ontario, Canada above a biosolids amended field. The study occurred during the autumn of 2004 (October–November) to capture the effects of cool weather conditions on the behaviour of mercury in the atmosphere. The initial concentration of total mercury (Hg) in the amended soil was relatively low (0.4 μg g −1±10%). A micrometeorological approach was used to infer the flux of GEM using a continuous two-level sampling system with inlets at 0.40 and 1.25 m above the soil surface to measure the GEM concentration gradient. The required turbulent transfer coefficients were derived from meteorological parameters measured on site. The average GEM flux over the study was 0.1±0.2 ng m −2 h −1(±one standard deviation). The highest averaged hourly GEM fluxes occurred when the averaged net radiation was highest, although the slight diurnal patterns observed were not statistically significant for the complete flux data series. GEM emission fluxes responded to various local events including the passage of a cold front when the flux increased to 2 ng m −2 h −1 and during a biosolids application event at an adjacent field when depositional fluxes peaked at −3 ng m −2 h −1. Three substantial rain events during the study kept the surface soil moisture near field capacity and only slightly increased the GEM flux. Average concentrations of RGM (2.3±3.0 pg m −3), Hg p (3.0±6.2 pg m −3) and GEM (1.8±0.2 ng m −3) remained relatively constant throughout the study except when specific local events resulted in elevated concentrations. The application of biosolids to an adjacent field produced large increases in Hg p (25.8 pg m −3) and RGM (21.7 pg m −3) concentrations only when the wind aligned to impact the experimental equipment. Harvest events (corn) in adjacent fields also corresponded to higher concentrations of GEM and Hg p but with no elevated peaks in RGM concentrations. Diurnal patterns were not statistically significant for RGM and Hg p at Maryhill.

Performance of a new diffusive sampler for Hg0 determination in the troposphere

Environmental context. Mercury is of concern to both the public and to the scientific community because it is found at high levels in some marine predators, prompting the US EPA and others to make guidelines restricting the consumption of some species. Most mercury in the environment is emitted to the atmosphere, but it is not known how it is transferred from the atmosphere to the marine environment. Therefore, it is important to study the connection between emission of mercury, its transport and removal from the atmosphere. We have developed a new sampler that is inexpensive, easy to use and with a sufficiently high detection limit that it can be used to measure the low mercury concentrations in the atmosphere at a reasonable time resolution. Abstract. Mercury behaves uniquely in the atmosphere due to its volatility and long lifetime. The existing methods for measuring atmospheric mercury are either expensive or labour intensive. The present paper presents a new measurement technique, the diffusive sampler, that is portable, inexpensive, easy to use, and does not need a power supply. The sampler is sufficiently sensitive that it can measure mercury at low ambient levels with an exposure time of 1 to 3 days. The sampler is based on the Radiello diffusive sampler, which was used to collect volatile organic compounds. In the present paper, the method is validated under controlled laboratory conditions. The uptake rate of the Radiello diffusive sampler is determined using known concentrations of gaseous elemental mercury, and is measured as a function of wind speed, relative humidity and temperature. The Radiello sampler has a detection limit of 0.14 ng m–3 for 1 day of exposure and thus can be used to measure mercury concentrations at the low levels found in ambient air. The Radiello sampler is therefore useful for mapping concentrations close to sources and sinks, in addition to ambient concentrations. For example, the sampler can be used to describe the geographical extent of Arctic mercury depletion episodes where gaseous elemental mercury is removed and stays close to 0 ng m–3 for days, and it can be a powerful tool for mapping gradients around point sources and other areas of interest.