Atmospheric Gaseous Elemental Mercury Research Articles

Statistical exploration of gaseous elemental mercury (GEM) measured at Cape Point from 2007 to 2011

Abstract. The authors evaluated continuous high-resolution gaseous elemental mercury (GEM) data from the Cape Point Global Atmosphere Watch (CPT GAW) station with different statistical analysis techniques. GEM data were evaluated by cluster analysis and the results indicated that two clusters, separated at 0.904 ng m−3, existed. The air mass history for the two-cluster solution was investigated by means of back-trajectory analysis. The air mass back-trajectory net result showed lower GEM concentrations originating from the sparsely populated semi-arid interior of South Africa and the marine environment, whereas higher GEM concentrations originated predominately along the coast of South Africa that most likely coincide with trade routes and industrial activities in urban areas along the coast. Considering the net result from the air mass back-trajectories, it is evident that not all low GEM concentrations are from marine origin, and similarly, not all high GEM concentrations have a terrestrial origin. Equations were developed by means of multi-linear regression (MLR) analysis that allowed for the estimation and/or prediction of atmospheric GEM concentrations from other atmospheric parameters measured at the CPT GAW station. These equations also provided some insight into the relation and interaction of GEM with other atmospheric parameters. Both measured and MLR calculated data confirm a decline in GEM concentrations at CPT GAW over the period evaluated.

Observations of atmospheric mercury in China: a critical review

Abstract. China presently contributes the largest amount of anthropogenic mercury (Hg) emission into the atmosphere in the world. Over the past decade, numerous studies have been conducted to characterize the concentration and forms of atmospheric Hg in China, which provide insights into the spatial and temporal distributions of atmospheric Hg through ground-based measurements at widely diverse geographical locations and during cruise and flight campaigns. In this paper, we present a comprehensive review of the state of understanding in atmospheric Hg in China. Gaseous elemental mercury (GEM) and particulate-bound mercury (PBM) measured at the remote sites in China are substantially elevated compared to the background values in the Northern Hemisphere. In Chinese urban areas, the highly elevated GEM, PBM and gaseous oxidized mercury (GOM) were mainly derived from local anthropogenic Hg emissions, whereas regional anthropogenic emissions and long-range transport from domestic source regions are the primary causes of the elevated GEM and PBM concentrations at remote sites. Using 7–9 years of continuous observations at a remote site and an urban site, a slight increase in atmospheric GEM (2.4–2.5 % yr−1) was identified (paired samples test: p < 0.01), which is in agreement with the increasing domestic anthropogenic emissions. Anthropogenic GEM emission quantity in China estimated through the observed GEM / CO concentration ratios ranged from 632 to 1138 t annually over the past decade, 2–3 times larger than published values using emission activity data. Modeling results and filed measurements show dry deposition is the predominant process for removing Hg from the atmosphere, 2.5–9.0 times larger than wet deposition, due to the elevated atmospheric GEM and PBM concentrations that facilitate dry deposition to terrestrial landscapes. Further studies to reconcile the observed and simulated Hg concentrations, to understand the impact of domestic emission reduction on Hg concentration and deposition and to delineate the role of Hg emission and deposition of China in the global Hg biogeochemical cycle, are needed.

Atmospheric mercury deposition and its contribution of the regional atmospheric transport to mercury pollution at a national forest nature reserve, southwest China.

Atmospheric mercury deposition by wet and dry processes contributes to the transformation of mercury from atmosphere to terrestrial and aquatic systems. Factors influencing the amount of mercury deposited to subtropical forests were identified in this study. Throughfall and open field precipitation samples were collected in 2012 and 2013 using precipitation collectors from forest sites located across Mt. Jinyun in southwest China. Samples were collected approximately every 2 weeks and analyzed for total (THg) and methyl mercury (MeHg). Forest canopy was the primary factor on THg and MeHg deposition. Simultaneously, continuous measurements of atmospheric gaseous elemental mercury (GEM) were carried out from March 2012 to February 2013 at the summit of Mt. Jinyun. Atmospheric GEM concentrations averaged 3.8 ± 1.5 ng m(-3), which was elevated compared with global background values. Sources identification indicated that both regional industrial emissions and long-range transport of Hg from central, northeast, and southwest China were corresponded to the elevated GEM levels. Precipitation deposition fluxes of THg and MeHg in Mt. Jinyun were slightly higher than those reported in Europe and North America, whereas total fluxes of MeHg and THg under forest canopy on Mt. Jiuyun were 3 and 2.9 times of the fluxes of THg in wet deposition in the open. Highly elevated litterfall deposition fluxes suggest that even in remote forest areas of China, deposition of atmospheric Hg(0) via uptake by vegetation leaf may be a major pathway for the deposition of atmospheric Hg. The result illustrates that areas with greater atmospheric pollution can be expected to have greater fluxes of Hg to soils via throughfall and litterfall.

Eddy covariance flux measurements of gaseous elemental mercury using cavity ring-down spectroscopy.

A newly developed pulsed cavity ring-down spectroscopy (CRDS) system for measuring atmospheric gaseous elemental mercury (GEM) concentrations at high temporal resolution (25 Hz) was used to successfully conduct the first eddy covariance (EC) flux measurements of GEM. GEM is the main gaseous atmospheric form, and quantification of bidirectional exchange between the Earth's surface and the atmosphere is important because gas exchange is important on a global scale. For example, surface GEM emissions from natural sources, legacy emissions, and re-emission of previously deposited anthropogenic pollution may exceed direct primary anthropogenic emissions. Using the EC technique for flux measurements requires subsecond measurements, which so far has not been feasible because of the slow time response of available instrumentation. The CRDS system measured GEM fluxes, which were compared to fluxes measured with the modified Bowen ratio (MBR) and a dynamic flux chamber (DFC). Measurements took place near Reno, NV, in September and October 2012 encompassing natural, low-mercury (Hg) background soils and Hg-enriched soils. During nine days of measurements with deployment of Hg-enriched soil in boxes within 60 m upwind of the EC tower, the covariance of GEM concentration and vertical wind speed was measured, showing that EC fluxes over an Hg-enriched area were detectable. During three separate days of flux measurements over background soils (without Hg-enriched soils), no covariance was detected, indicating fluxes below the detection limit. When fluxes were measurable, they strongly correlated with wind direction; the highest fluxes occurred when winds originated from the Hg-enriched area. Comparisons among the three methods showed good agreement in direction (e.g., emission or deposition) and magnitude, especially when measured fluxes originated within the Hg-enriched soil area. EC fluxes averaged 849 ng m(-2) h(-1), compared to DFC fluxes of 1105 ng m(-2) h(-1) and MBR fluxes of 1309 ng m(-2) h(-1). This study demonstrated that a CRDS system can be used to measure GEM fluxes over Hg-enriched areas, with a conservative detection limit estimate of 32 ng m(-2) h(-1).

An approach estimating bidirectional air‐surface exchange for gaseous elemental mercury at AMNet sites

AbstractThe bidirectional air‐surface exchange for gaseous elemental mercury (GEM) and existing measurements of the compensation points over a variety of canopy types are reviewed. Deposition and emission of GEM are dependent on several factors such as the type of canopy, temperature, season, atmospheric GEM concentrations, and meteorological conditions, with compensation points varying between 0.5 and 33 ng m−3. Emissions tend to increase from the spring to summer seasons, as the GEM accumulates in the foliage of the vegetation. A strong dependence on solar radiation has been observed, with higher emissions under light conditions. A bidirectional air‐surface exchange flux model is proposed for estimating GEM fluxes at a two‐hourly time resolution for the National Atmospheric Deposition Program's, Atmospheric Mercury Network (AMNet) sites. Compared to the unidirectional dry deposition model used in Zhang et al. (2012), two additional parameters, stomatal and soil emission potential, were needed in the bidirectional model and were chosen based on knowledge gained in the literature review and model sensitivity test results. Application of this bidirectional model to AMNet sites have produced annual net deposition fluxes comparable to those estimated in Zhang et al. (2012) at the majority of the sites. In this study, the net GEM dry deposition has been estimated separately for each dominant land use type surrounding each site, and this approach is also recommended for future calculations for easy application of the results to assessments of the mercury effects on various ecosystems.

Parameterizing Soil Emission and Atmospheric Oxidation-Reduction in a Model of the Global Biogeochemical Cycle of Mercury

Using the GEOS-Chem atmosphere-land-ocean coupled mercury model, we studied the significances of two processes, soil emission and atmospheric oxidation-reduction, in the global biogeochemical cycling of mercury and their parametrization to improve model performance. Implementing an empirical equation for soil emission flux (Esoil) including soil mercury concentration, solar radiation, and surface air temperature as parameters enabled the model to reproduce the observed seasonal variations of Esoil, whereas the default setting, which uses only the former two parameters, failed. The modified setting of Esoil also increased the model-simulated atmospheric concentration in the summertime surface layer of the lower- and midlatitudes and improved the model reproducibility for the observations in Japan and U.S. in the same period. Implementing oxidation of atmospheric gaseous elemental mercury (Hg(0)) by ozone with an updated rate constant, as well as the oxidation by bromine atoms (Br) in the default setting, improved the model reproducibility for the dry deposition fluxes observed in Japan. This setting, however, failed to reproduce the observed seasonal variations of atmospheric concentrations in the Arctic sites due to the imbalance between oxidation and reduction, whereas the model with Br as the sole Hg(0) oxidant in the polar atmosphere could capture the variations.

A unique seasonal pattern in dissolved elemental mercury in the South China Sea, a tropical and monsoon‐dominated marginal sea

AbstractA unique seasonal pattern in dissolved elemental mercury (DEM) was observed in the tropical monsoon‐dominated South China Sea (SCS). The DEM concentration varied seasonally, with a high in summer of 160 ± 40 fM (net evasion 580 ± 120 pmol m−2 d−1, n = 4) and a low in winter of 60 ± 30 fM (net invasion −180 ± 110, n = 4) and showed a positive correlation with sea surface temperature (SST). The elevated DEM concentration in summer appears mainly abiologically driven. In winter, the SCS acts as a sink of atmosphere Hg0 as a result of low SST and high wind of the year, enhanced vertical mixing, and elevated atmospheric gaseous elemental mercury. Annually, the SCS serves as a source of Hg0 to the atmosphere of 300 ± 50 pmol m−2 d−1 (385 ± 64 kmol Hg yr−1, ~2.6% of global emission in ~1% of global ocean area), suggesting high regional Hg pollution impacts from the surrounding Mainland (mostly China).

Preliminary results from a continuous record of atmospheric gaseous mercury at the coastal station Dumont d’Urville in Antarctica

While the tropospheric reactivity of mercury (Hg) in the Arctic is more and more documented only a few attempts were made to study the Hg cycle in the Southern Polar Regions. The role of the Antarctic continent and its influence on the global geochemical cycle of mercury is unclear today, and is certainly under evaluated by current models. Here, we present the first continuous high-time-resolution measurements of atmospheric gaseous elemental mercury (GEM) in East Antarctica from February 2010 to March 2011 at the coastal research station Dumont d’Urville (DDU) (66°40’S, 140°01’E, 43 m asl). We report an annual mean level of 1.062 ± 0.321 ng/m3 with well-marked daily fluctuations from October to January. An intense reactivity originated from the atmospheric boundary layer of the Antarctic plateau under sunlight conditions is observed at DDU. Partly GEM-depleted air masses are exported from the continent and dramatically influence the GEM record at DDU. From November to January, surface waters of the Southern Ocean are an important source of GEM.

How relevant is the deposition of mercury onto snowpacks? – Part 2: A modeling study

Abstract. An unknown fraction of mercury that is deposited onto snowpacks is revolatilized to the atmosphere. Determining the revolatilized fraction is important since mercury that enters the snowpack meltwater may be converted to highly toxic bioaccumulating methylmercury. In this study, we present a new dynamic physically-based snowpack/meltwater model for mercury that is suitable for large-scale atmospheric models for mercury. It represents the primary physical and chemical processes that determine the fate of mercury deposited onto snowpacks. The snowpack/meltwater model was implemented in Environment Canada's atmospheric mercury model GRAHM. For the first time, observed snowpack-related mercury concentrations are used to evaluate and constrain an atmospheric mercury model. We find that simulated concentrations of mercury in both snowpacks and the atmosphere's surface layer agree closely with observations. The simulated concentration of mercury in both in the top 30 cm and the top 150 cm of the snowpack, averaged over 2005–2009, is predominantly below 6 ng L−1 over land south of 66.5° N but exceeds 18 ng L−1 over sea ice in extensive areas of the Arctic Ocean and Hudson Bay. The average simulated concentration of mercury in snowpack meltwater runoff tends to be higher on the Russian/European side (>20 ng L−1) of the Arctic Ocean than on the Canadian side (<10 ng L−1). The correlation coefficient between observed and simulated monthly mean atmospheric surface-level gaseous elemental mercury (GEM) concentrations increased significantly with the inclusion of the new snowpack/meltwater model at two of the three stations (midlatitude, subarctic) studied and remained constant at the third (arctic). Oceanic emissions are postulated to produce the observed summertime maximum in concentrations of surface-level atmospheric GEM at Alert in the Canadian Arctic and to generate the summertime volatility observed in these concentrations at both Alert and Kuujjuarapik on subarctic Hudson Bay, Canada. We find that the fraction of deposited mercury that is revolatilized from snowpacks increases with latitude from 39% between 30 and 45° N, to 57% from 45 to 60° N, 67% from 60 to 66.5° N, and 75% polewards of 66.5° N on an annual basis. Combining this latitudinal gradient with the latitudinally increasing coverage of snowpacks causes yearly net deposition as a fraction of gross deposition to decrease from 98% between 30 and 45° N to 89% between 45 and 60° N, 73% between 60 and 66.5° N, and 44% within the Arctic Circle. The yearly net deposition and net accumulation of mercury at the surface within the Arctic Circle north of 66.5° N are estimated at 153 and 117 Mg, respectively. We calculate that 58 and 50 Mg of mercury are deposited annually to the Arctic Ocean directly and indirectly via melting snowpacks, respectively. For terrestrial surfaces within the Arctic Circle, we find that 29 and 16 Mg of mercury are deposited annually directly and indirectly via melting snowpacks, respectively. Within the Arctic Circle, multi-season snowpacks on land and over sea ice gained, on average, an estimated 0.1 and 0.4 Mg yr−1 mercury, respectively, from 2000–2005. The developed snowpack/meltwater model can be used for investigating the impact of climate change on the snowpack/atmosphere exchange of mercury.

Speciated atmospheric mercury and its potential source in Guiyang, China

Abstract Speciated atmospheric mercury (Hg) including gaseous elemental mercury (GEM), particulate Hg (PHg), and reactive gaseous Hg (RGM) were continuously measured at an urban site in Guiyang city, southwest China from August to December 2009. The averaged concentrations for GEM, PHg, and RGM were 9.72 ± 10.2 ng m −3 , 368 ± 676 pg m −3 , and 35.7 ± 43.9 pg m −3 , respectively, which were all highly elevated compared to observations at urban sites in Europe and North America. GEM and PHg were characterized by similar monthly and diurnal patterns, with elevated levels in cold months and nighttime, respectively. In contrast, RGM did not exhibit clear monthly and diurnal variations. The variations of GEM, PHg, and RGM indicate the sampling site was significantly impacted by sources in the city municipal area. Sources identification implied that both residential coal burning and large point sources were responsible to the elevated GEM and PHg concentrations; whereas point sources were the major contributors to elevated RGM concentrations. Point sources played a different role in regulating GEM, PHg, and RGM concentrations. Aside from residential emissions, PHg levels was mostly affected by small-scale coal combustion boilers situated to the east of the sampling site, which were scarcely equipped or lacking particulate control devices; whereas point sources situated to the east, southeast, and southwest of the sampling played an important role on the distribution of atmospheric GEM and RGM.

Atmospheric gaseous elemental mercury (GEM) over a coastal/rural site downwind of East China: Temporal variation and long-range transport

Abstract Although much attention has been paid to the mercury pollution in China, limited field studies have been conducted to explore the atmospheric behavior of mercury. To investigate the temporal variation and long-range transport of atmospheric gaseous elemental mercury (GEM or Hg(0)), the GEM measurements covering four different seasons were performed at a coastal/rural site of the Yellow Sea downwind of East China. Hourly mean concentrations of GEM measured by RA–915+ mercury analyzer over the entire study (four different time periods between July 2007 and May 2009) were 2.31 ± 0.74 ng m−3 with a range of 1.12–7.01 ng m−3. The results showed moderate seasonal variations with high levels in cold seasons (winter: 2.53 ± 0.77 ng m−3 and spring: 2.34 ± 0.54 ng m−3) and low levels in warm seasons (summer: 2.28 ± 0.82 ng m−3 and fall: 2.16 ± 0.84 ng m−3). Over the each campaign a diurnal variation of GEM was observed consistently with peak levels in daytime and low levels in late night and early morning. The pollution rose and NOAA–HYSPLIT back-trajectory model analyses indicated that the elevated GEM was transported to the sampling site from the regional sources of East China and Korea peninsula–Japan. Air masses originated from the East China Sea and the regions of Continental East Asia with low emission strengths of atmospheric mercury (e.g., the east Russia, the north Inner Mongolia and the Bohai Sea) showed the decreased GEM levels.

Source, concentration, and distribution of elemental mercury in the atmosphere in Toronto, Canada

Atmospheric gaseous elemental mercury [GEM] at 1.8, 4, and 59 m above ground, in parking lots, and in indoor and outdoor air was measured in Toronto City, Canada from May 2008–July 2009. The average GEM value at 1.8 m was 1.89 ± 0.62 ng m −3. The GEM values increased with elevation. The average GEM in underground parking lots ranged from 1.37 to 7.86 ng m −3 and was higher than those observed from the surface parking lots. The GEM in the indoor air ranged from 1.21 to 28.50 ng m −3, was higher in the laboratories than in the offices, and was much higher than that in the outdoor air. All these indicate that buildings serve as sources of mercury to the urban atmosphere. More studies are needed to estimate the contribution of urban areas to the atmospheric mercury budget and the impact of indoor air on outdoor air quality and human health.

Ground and shipboard measurements of atmospheric gaseous elemental mercury over the Yellow Sea region during 2007–2008

Abstract The first ever shipboard measurements of atmospheric gaseous elemental mercury (GEM) over the Yellow Sea were carried out. Ground measurements were also performed at background and urban sites surrounding the Yellow Sea during 2007–2008. The GEM mean concentrations obtained from ground measurements at Ningbo, Chengshantou, and Deokjeok, and from shipboard measurements for the routes of Incheon–Qingdao, Incheon–Weihai, and Incheon–Jeju were 3.79 ± 1.29, 2.07 ± 0.91, 1.79 ± 0.80, 1.82 ± 0.51, 2.03 ± 0.66, and 2.43 ± 0.59 ng m−3, respectively. Compared with the GEM background concentration in the northern hemisphere, the slightly higher GEM regional background concentration of 2.08 ± 0.85 ng m−3 over the Yellow Sea region, based on shipboard measurements and ground measurements at background sites, gave implications for the impact of anthropogenic mercury sources surrounding the Yellow Sea. Shipboard measurements over the Yellow Sea showed a decrease of mercury concentration compared with aircraft measurements during ACE-ASIA campaign in 2001, though it was still generally higher than those from other seas or oceans around the world. The contrasting patterns in seasonal and diurnal variations of GEM concentration between background and urban sites were apparent due to the influence of different sources; for example, natural sources, such as vegetative and foliar emissions in background area, and local anthropogenic sources, such as coal combustion in urban area. The significantly elevated GEM concentrations at Deokjeok, a Korean background site, during the spring of 2008 were attributed to the long-range transport from the southern part of Liaoning province, one of the heaviest mercury-polluted areas in China.

ATMOSPHERIC MERCURY MEASUREMENTS AT CAPE POINT, SOUTH AFRICA

Over the 1995-2009 period the gaseous elemental mercury (GEM) concentrations have decreased by about 0.04 ng m-3 yr-1 -at Cape Point (CPT). A reduction of the same magnitude is indicated by measurements during intermittent ship cruises, implying a homogeneous distribution of GEM concentrations in the Southern Hemisphere (SH) and a 30% reduction of its atmospheric burden. Almost all GEM measurements in the Northern Hemisphere (NH) point to a substantial decrease but the trends are inhomogeneous, most likely due to a variable source distribution. However, measurements in the NH during ship cruises suggest a trend of similar magnitude. A decrease in the total atmospheric GEM burden by about 30% is inconsistent with the current mercury budgets. The most probable explanation for this is subsiding re-emissions from the legacy of large past emissions.
 High-resolution data since 2007 revealed depletion (DES) as well as pollution events (PEs). Both types are embedded in air masses ranging from marine background to continental. The DES observed at Cape Point are a local phenomenon (<100 km) and are the first mercury depletion events reported outside the Polar Regions. In contrast to polar DES, the DES at CPT are not accompanied by concurrent O3 depletion. They mostly appear at wind speeds < 10 m s-1 and their predominating occurrence between 11 and 18 hours suggests a photochemical destruction mechanism which could not be explained yet.
 GEM correlates with CO, C02, and CH4 during most PES at CPT (GEM levels > 1.3 ng m-3) and with 222Rn during about half the events. Most of the observed GEM/CO emission ratios are within the range bracketed by values reported for biomass burning and industrial/urban emissions, thus suggesting a mixture of both. No significant differences of GEM/CO and GEM/C02 could be found between different source regions defined by backward trajectories. This implies that exceptionally high emissions ascribed to the Gauteng region in global mercury inventories are overestimated.

Atmospheric gaseous elemental mercury (GEM) concentrations and mercury depositions at a high-altitude mountain peak in south China

Abstract. China is regarded as the largest contributor of mercury (Hg) to the global atmospheric Hg budget. However, concentration levels and depositions of atmospheric Hg in China are poorly known. Continuous measurements of atmospheric gaseous elemental mercury (GEM) were carried out from May 2008 to May 2009 at the summit of Mt. Leigong in south China. Simultaneously, deposition fluxes of THg and MeHg in precipitation, throughfall and litterfall were also studied. Atmospheric GEM concentrations averaged 2.80±1.51 ng m−3, which was highly elevated compared to global background values but much lower than semi-rural and industrial/urban areas in China. Sources identification indicates that both regional industrial emissions and long range transport of Hg from central, south and southwest China were corresponded to the elevated GEM level. Seasonal and diurnal variations of GEM were observed, which reflected variations in source intensity, deposition processes and meteorological factors. Precipitation and throughfall deposition fluxes of THg and MeHg in Mt. Leigong were comparable or lower compared to those reported in Europe and North America, whereas litterfall deposition fluxes of THg and MeHg were higher compared to Europe and North America. This highlights the importance of vegetation to Hg atmospheric cycling. In th remote forest ecosystem of China, deposition of GEM via uptake of foliage followed by litterfall was very important for the depletion of atmospheric Hg. Elevated GEM level in ambient air may accelerate the foliar uptake of Hg through air which may partly explain the elevated litterfall deposition fluxes of Hg observed in Mt. Leigong.

Mercury degassing from forested and open field soils in Rondônia, Western Amazon, Brazil

A Teflon ® dynamic flux chamber was used to characterize Gaseous Elemental Mercury (GEM) flux from forested and open field soils in a highly changing environment in Rondônia State, western Amazon. We simultaneously analyzed meteorological parameters at the soil level relating GEM fluxes to soil temperature, air humidity, soil moisture, solar radiation, and speed and wind direction. We also examined variations of atmospheric GEM concentration. GEM fluxes during the day and night in the open field site were significantly different (17 ± 14 ng m −2 h −1 and 0.9 ± 1.9 ng m −2 h −1, for day and night, respectively), but were similar within the forest site (4.8 ± 1.4 ng m −2 h −1 and 4.4 ± 1.8 ng m −2 h −1 for day and night periods, respectively). A comparison between 24-h periods averages in the two sites showed much larger emission from the open field site. GEM fluxes at the open field site were positively correlated with soil moisture, solar irradiation and soil temperature and inversely correlated with air humidity. At the forest site GEM fluxes showed no correlation with meteorological variables. At the open field site GEM concentrations significantly correlated with GEM flux, at least during the day. At night in the open field site and during the day and night at the forest site no correlation was found between GEM fluxes and GEM concentrations in the ambient air. Higher emissions from the open field site support earlier studies showing larger Hg remobilization following forest conversion to pasture.

Annual atmospheric mercury species in Downtown Toronto, Canada

Real-time concentrations of atmospheric gaseous elemental mercury (GEM), reactive gaseous mercury (RGM), and mercury associated with particles having sizes <2.5 microm (P-Hg < 2.5) were simultaneously measured in downtown Toronto from December 2003 to November 2004. The annual mean concentrations of GEM, P-Hg < 2.5 and RGM were 4.5 +/- 3.1 ng m(-3) (99.2%), 21.5 +/- 16.4 pg m(-3) (0.5%) and 14.2 +/- 13.2 pg m(-3) (0.3%), respectively. The concentrations for all the measured Hg species were highly variable throughout the year and were lower in winter than in the other three seasons. The maximum concentrations of Hg species were observed in June and were a result of the high number of Hg spikes (using [GEM] >10 ng m(-3) as an indicator) that occurred in the month. Nighttime (between 9pm-6am) concentrations of Hg species were higher than those of daytime. The results revealed: (1) an urban area is a continuous source of Hg species that have the potential to pose impacts on local, regional and global scales; (2) local/regional anthropogenic sources contributed significantly to the levels and the distributions of the Hg species in the urban atmosphere. More studies are needed to identify and quantify the anthropogenic sources of Hg and the Hg species emitted from these sources; (3) surface emission and photochemical reactions (including the reactions involving ozone) did not have significant influence on the levels of Hg species and their distribution in the urban atmosphere.

Atmospheric gaseous elemental mercury in downtown Toronto

Continuous measurements of gaseous elemental mercury (GEM) in downtown Toronto were conducted from June 2001–February 2002. Ambient air was sampled at 3.5 and 7 m above ground in a canopy over a sidewalk. The quarter hourly mean concentrations were found at 2.39±2.05 ng m −3 ( N=10,658) for the lower sampling level, and 2.57±2.39 ng m −3 ( N=10,628) for the upper sampling level. The average of both sampling levels (2.48 ng m −3) was 60% higher than the average of Canadian background emission (1.55 ng m −3, Alert). Seasonal concentrations showed the effects of the temperature on the volatilization of Hg 0. Higher GEM was found in the summer time (20 June–19 September) at 3.03±2.13 ng m −3 (lower level) and 3.31±2.56 ng m −3 (upper level) while lower values were observed in the fall (20 September–19 December) at 1.84±0.87 ng m −3 (lower level) and 1.97±1.38 ng m −3 (upper level). Log normal probability distribution of the GEM concentration was verified and the double peak hourly average diurnal distribution of GEM concentration was observed in our study.

Different mercury species in the atmosphere over the municipal solid waste landfills

China and its afect on the global scale.thus.remain largely unknown.This paper describes the on—going projects on the studies of background mercury species in the atmosphere on the Tibet Plateau an d Changbai Mounmin , the efect of human activities on mercury distribution in urban environm ent and industrial areas.A fuly automated mercury speciation system (Tekran.Toronto. Canada1 is used to study mercury species in the atm osphere.This system employs specially designed devices for selective colection of gaseous elemental mercury(GEM),gaseous oxidized inorganic mercury(GOIM),and mercury associated with fine particles.The colected mercury species are thermaly desorbed and analyzed by cold vapor atomic fluorescence spectrometry(CVAFS).Mercury species in the samples of river water,wel water,atm ospheric precipitate,river sediment,soil,an d fruits were measured folowing USEPA methods.Preliminary results showed that the atm ospheric background GEM leve1.