Mercury Wet Deposition Research Articles

Wet and dry deposition fluxes of mercury in Japan

Wet and dry deposition fluxes of mercury were measured concurrently from December 2002 to November 2003 at 10 sites in Japan (nine sites for dry deposition measurements). Precipitation and dry deposition (gases and particles) were collected every half-month using an automatic wet and dry deposition sampler. This sampler is composed of a precipitation sampler and a water surface sampler for dry deposition. The results showed that wet deposition fluxes of mercury increase generally during summer when the precipitation amount increases. In contrast, the seasonal variations of the dry deposition fluxes were very small compared to those of the wet deposition fluxes. It was found that wet deposition plays a dominant role in mercury deposition in Japan, contributing fluxes ranging from 0.99 to 2.2 times (1.6 times on average at nine sites) those of the dry deposition fluxes. There was a high correlation between the annual wet deposition flux of mercury and annual precipitation amount (r2=0.73, P<0.01). Thus, about 70% of the variance of mercury wet deposition in Japan is explained by precipitation amount. This is probably because mercury wet deposition is dominated by the scavenging of reactive gaseous mercury (RGM) by precipitation via oxidation of gaseous elemental mercury (Hg0) in the gas and aqueous phases. In addition, a similar relationship between the annual wet deposition flux and precipitation amount (r2=0.55, P<0.001) was observed at the Mercury Deposition Network (MDN) sites in North America, suggesting that about 55% of the variance of mercury wet deposition is due to precipitation amount.

Long-term Atmospheric Mercury Wet Deposition at Underhill, Vermont

Section 112(m) of the 1990 Clean Air Act Amendments, referred to as the Great Waters Program, mandated an assessment of atmospheric deposition of hazardous air pollutants (HAPs) to Lake Champlain. Mercury (Hg) was listed as a priority HAP and has continued to be a high priority for a number of national and international programs. An assessment of the magnitude and seasonal variation of atmospheric Hg levels and deposition in the Lake Champlain basin was initiated in December 1992 which included event precipitation collection, as well as collection of vapor and particle phase Hg in ambient air. Sampling was performed at the Proctor Maple Research Center in Underhill Center, VT. The range in the annual volume-weighted mean concentration for Hg in precipitation was 7.8-10.5 ng/l for the 11-year sampling period and the average amount of Hg deposited with each precipitation event was 0.10 microg/m2. The average amount of Hg deposited through precipitation each year from 1993 to 2003 was 9.7 microg/m2/yr. A seasonal pattern for Hg in precipitation is clearly evident, with increased Hg concentrations and deposition observed during spring and summer months. While a clear trend in the 11-year event deposition record at Underhill was not observed, a significant decrease in the event max-to-monthly ratio was observed suggesting that a major source influence was controlled over time. Discrete precipitation events were responsible for significant fractions of the monthly and annual loading of Hg to the forested ecosystem in Vermont. Monthly-averaged temperatures were found to be moderately correlated with monthly volume-weighted mean Hg concentrations (r2 = 0.61) and Hg deposition (r2 = 0.67) recorded at the Vermont site. Meteorological analysis indicated the highest levels of Hg in precipitation were associated with regional transport from the west, southwest, and south during the warmer months.

Global source attribution for mercury deposition in the United States.

A multiscale modeling system that consists of a global chemical transport model (CTM) and a nested continental CTM was used to simulate the global atmospheric fate and transport of mercury and its deposition over the contiguous United States. The performance of the CTMs was evaluated against available data. The coefficient of determination (r2) for observed versus simulated annual mercury wet deposition fluxes over North America was 0.50 with average normalized error and bias of 25% and 11%, respectively. The CTMs were used to conduct a global source attribution for selected receptor areas. Three global emission scenarios were used that differed in their distribution of background emissions among direct natural emissions and re-emissions of natural and anthropogenic mercury. North American anthropogenic sources were calculated to contribute only from 25 to 32% to the total mercury deposition over the continental United States. At selected receptors, the contribution of North American anthropogenic emissions ranges from 9 to 81%; Asian anthropogenic emissions were calculated to contribute from 5 to 36%; natural emissions were calculated to contribute from 6 to 59%.

Divalent inorganic reactive gaseous mercury emissions from a mercury cell chlor-alkali plant and its impact on near-field atmospheric dry deposition

Abstract The emission of inorganic divalent reactive gaseous mercury (RGM) from a mercury cell chlor-alkali plant (MCCAP) cell building and the impact on near field (100 km) dry deposition was investigated as part of a larger collaborative study between EPA, University of Michigan, Oak Ridge National Laboratory, Chlorine Institute, and Olin Corporation in February 2000. Measurements in the cell building roof vent showed that RGM constituted 2.1±0.7% (median±variance) of the concurrently measured elemental gaseous mercury (Hg 0 ). This relationship was used to calculate an estimated RGM emission rate from the cell building roof vent of 10.4 g day −1 . The percentage of RGM/Hg 0 at ambient monitoring sites 350 m (1.5%) and 800 m (1.3%) away while being impacted by cell building emissions suggests the rapid deposition of RGM species. The observed 2% relative emission of RGM/Hg 0 was substantially lower than the 30% estimate utilized by EPA to model the impact of MCCAPs for the 1997 Mercury Report to Congress. However, the MCCAP was still found to present a significant impact on near field mercury atmospheric dry deposition. A Lagrangian transport and deposition modeling framework using only emissions from the MCCAP found the mean annualized dry deposition of mercury within a 10 km radius of the facility contributed the annual equivalent of 4.6 μg m −2 . For comparison, the total annual wet mercury deposition measured at the Savannah River National Mercury Deposition Network sampling site ∼30 km away was 9.8 μg m −2 .

Preliminary study of the distribution of gaseous mercury species in the air of Guiyang city, China

Total gaseous mercury (TGM) in ambient air consists of Hg 0 and reactive gaseous mercury (RGM) in general. Although RGM only constitutes a small portion of TGM in the air, it contributes the most to both dry and wet deposition of mercury from the atmosphere. TGM and RGM concentrations in ambient air at one site of Guiyang City were determined in March 2002. TGM concentrations were monitored using an automated mercury vapor analyzer Tekran2537A, and RGM in ambient air was sampled using KCl coated tubular denuders. The sampled RGM denuders were analyzed using thermal desorption coupled with CVAFS detection. The average concentrations of TGM and RGM are 7.09 ng/m 3 and 37.5 pg/m 3 respectively during the sampling period. The primary anthropogenic source for both Hg 0 and RGM is coal combustion in the study area. TGM concentrations are significantly elevated comparing to the global background values, whereas RGM concentrations are only slightly higher than the reported values in remote areas in Europe and US. RGM only constitutes 0.5% of TGM in the air at the sampling period. There is a significant negative correlation between RGM concentration and relative humidity (RH), with a coefficient correlation of 0.39 (α<0.01). High relative humidity during the sampling is responsible for the relatively low RGM concentrations observed.

Estimation of mercury wet deposition in the tributary sub-basins of the Negro river (Amazon-Brazil) using RS/GIS tools

Recent studies have shown high concentrations of Hg in fish, soil, lakes and rivers of the Negro river basin. These concentrations were surprisingly high when considering the scarcity of anthropogenic point sources in the region (Fadini and Jardim, 2001). In order to investigate the role of wet deposition in the mercury biogeochemistry cycle in this basin, Hg deposition was estimated for 18 tributary sub-basins of the Negro river, covering an area of nearly 700000 km 2 . Mercury wet deposition estimate was done by combining analytical data obtained from total Hg measurements in bulk precipitation (8 measurements between 1997 and 2002), Remote Sensoring (RS) and GIS (Geographic Information System) tools, with the help of orbital images from the JERS-1 SAR project (Global Rain Forest Mapping Project, South America- Amazon Basin), Amazon rainfall map (Sombroek, 2001) and SPRING (Geographic information of processing system) from INPE (Brazilian National Institute of Space Research). For each sub-basin, Hg wet deposition flux (ton/km 2 .yr) and the annual amount of Hg (ton/yr) deposited on the area were estimated. The result allowed a clear picture of each sub-basins, by looking for a relation between the wet deposition, the drainage characteristics of each sub-basin and the Hg concentration in the water column.

Simulation of the fate and transport of mercury in North America

A multiscale modeling system that includes a global model and a nested continental model is applied to simulate the global cycling of atmospheric mercury and its fate and transport over North America. The models show satisfactory performance with a coefficient of determination of 0.81 for mercury wet deposition over North America. The models are used to estimate source attribution of mercury deposition in the United States. On average, 73% of mercury deposited in the contiguous United States is calculated to originate from the global background.

Occurrence, emissions and deposition of mercury during coal combustion in the province Guizhou, China

Forty-eight coal samples from the major coal mines in Guizhou were collected by means of subterranean channel sampling. The average mercury content in coal from this Chinese province is 0.53 mg kg-1, which is substantially higher than coal produced in any other province of China. A strong link is proposed to exist between atmospheric mercury emissions and the combustion of coal. During the last two decades, the amount of mercury emitted from coal combustion in Guizhou has increased invariably to 8.3 tons in 1998. Being concentrated to the pyrite fraction in the coal, the implementation of physical coal cleaning is likely to be an effective way to reduce the mercury content. Total and fractionated mercury in air and precipitation was measured in the provincial capital. During a measurement campaign in October 1999, the reactive gaseous mercury (RGM) concentration averaged at 450 pg m-3, which is much higher than that in pristine area (less than 20 pg m-3). The average total mercury in rainwater of 1996 was estimated to be 33 ng L-1, and the total annual wet deposition of mercury in the area was 39 g km-2 in 1996.

Examining Source-Receptor Relationships for Mercury in Scandinavia Modelled and Empirical Evidence

The atmosphere remains the major source of mercuryin Swedish ecosystems. Since the late eighties,atmospheric emissions of mercury have drasticallydecreased in Europe. Wet deposition of mercury hasdecreased over the last decade but still exhibitsa clear south-to-north gradient, greatlyinfluenced by source areas in northern and centralEurope. The decreases in emissions can beattributed to both direct measures to close knownpoint sources and a declining economy and energyconsumption in many East European countries.Further reductions of mercury emissions willrequire that other source categories such asindirect emissions from mercury-containingproducts and crematories are be considered.

The Northeast States and Eastern Canadian Provinces mercury study: a framework for action: summary of the Canadian chapter

The objective of this paper is to give an overview of the findings of the Canadian chapter of the Northeast States and Eastern Canadian Provinces Mercury Study, which was conducted between 1995 and 1998. The Canadian chapter provided information on mercury emissions, sources and levels in air, water, biota and humans. Industry, governments and universities provided information for the Canadian chapter. The study showed that the Northeast States and Eastern Canadian Provinces (NES/ECP) is a region impacted by airborne mercury. Annual mercury emissions for the NES/ECP region are estimated to be approximately 19 t (12%) of the combined Canadian and US national anthropogenic mercury emissions of 155 t/year. 210Pb-dated lake sediment cores from Atlantic Canada showed a mercury enrichment factor of 2.5 for coastal sites with mercury increases starting in 1860. Regional mercury wet deposition for the NES/ECP region was 7–11 μg/m 2/year. Provincial and federal fish health advisories have been updated in the ECP for children and women of child-bearing age limiting the consumption of freshwater fish, as well as fresh or frozen shark, tuna or swordfish.

On artificial dilution of point source mercury emissions in a regional atmospheric model

Previously, we developed and applied a regional atmospheric mercury model to a domain covering most of North America at a horizontal grid resolution of 100 km. The implication of using this coarse resolution is that point sources of mercury emissions are instantaneously spread over a grid volume of horizontal dimensions 100×100 km 2 and a vertical dimension equal to the depth of the grid cell where the point source emissions are released. Since point sources comprise a significant majority of a regional mercury emissions inventory, it is important to understand what effect this artificial dilution may have on calculated mercury concentrations and deposition fluxes. To understand this effect, we conducted model simulations using a finer grid, embedded within the original coarse grid, over a sub-domain that includes over 50% of the largest mercury point sources in the north-eastern United States. The horizontal resolution of the fine grid is 20 km, i.e. it is five times smaller than that of the coarse grid. We compared short-term (daily) and long-term (annual) averaged mercury concentrations, and deposition (wet and dry) fluxes on the coarse and fine grids. As expected, the effect of grid resolution is more clearly seen in close proximity to point sources than at remote locations. For short-term averages near major point sources, the peak concentrations and dry deposition fluxes of mercury from the fine grid are almost a factor of two greater than the corresponding estimates from the coarse grid. At remote locations, however, the concentrations and dry deposition peaks estimated by the two model grid resolutions are more comparable. For total wet deposition of mercury, the distinction between the fine and the coarse grid model results is less significant, regardless of the location. This could be due to the redistribution of precipitation fields or the effect of mercury aqueous chemistry. The effect of grid resolution is more important when model estimates are averaged over short time periods, e.g. daily, as opposed to over long periods, e.g. seasonally and annually.

Modeling assessment of transport and deposition patterns of anthropogenic mercury air emissions in the United States and Canada

In December 1997, the U.S. Environmental Protection Agency submitted its mercury study report to Congress, which included a modeling assessment of the long-range transport and deposition of mercury from various residential and industrial sources within the United States, based on numerical simulations of elemental mercury gas, divalent mercury gas and particulate mercury, using a special version of the Regional Lagrangian Model of Air Pollution (RELMAP). Observations of the deposition of total precipitated mercury at several locations within the U.S. were compared to the modeling results in order to evaluate the accuracy of the RELMAP simulations. However, the lack of Canadian mercury emissions data in the RELMAP modeling limited the usefulness of this model evaluation at locations near the Canadian border. An inventory of Canadian mercury emissions obtained from Environment Canada has now been added to the RELMAP mercury modeling, and the previous simulations and evaluation of modeled wet deposition have been repeated. The results indicate that emissions of mercury from Canada, as represented by the new inventory, do not significantly impact simulated wet deposition over the United States, nor the general results of the previous model evaluation. Analyses of the simulated transport and deposition patterns of mercury emissions from both the United States and Canada are presented, along with the simulated fraction of total mercury wet deposition, separately attributable to sources within each nation.

Six-Year Trend (1990−1995) of Wet Mercury Deposition in the Upper Midwest, U.S.A.

Total wet mercury deposition was monitored weekly at six Upper Midwest, USA, sites for a period of six years, 1990--1995, to assess temporal and spatial patterns and contributions to surface waters. Annual wet mercury deposition averaged 7.4 {micro}g Hg/m{sup 2}{center{underscore}dot}yr and showed significant variations between sites and increased trends averaging 0.60 {micro}g Hg/m{sup 1}{center{underscore}dot}yr [8%/yr] over the period. Warm (rain) season wet mercury deposition was found to average 77% of total annual wet deposition. Warm (rain) and cold (snow) season trends showed increases of 0.31 [5.5%/yr] and 0.29 {micro}g Hg/m{sup 2}{center{underscore}dot}yr [17%/yr], respectively. Average annual precipitation depth showed a nonsignificant increase of 0.25 cm/yr [0.4%/yr] for the period. Differences in precipitation depth, mercury concentrations, and wet mercury deposition among sites were noted. Methylmercury wet deposition, measured in 36 weekly samples, averaged about 0.18 ng/L [1.5% of total mercury] in rain and strongly correlated with total mercury, major ions, and precipitation depth.

Sensitivity of simulated atmospheric mercury concentrations and deposition to model input parameters

Previously, we have simulated the atmospheric transport and fate of mercury emissions in North America and derived estimates of ambient concentrations and dry and wet deposition of mercury. In this study we quantify sensitivity of the derived estimates to model input parameters that we believe have the largest potential to influence model estimates. We vary five input parameters: emission speciation, Hg(II) dry deposition velocity, precipitation amount, concentration of redox species, and Hg(II) boundary conditions, within their plausible range of values. Our results show that emission speciation has the largest influence and Hg(II) boundary conditions have the smallest influence on the derived estimates. The sensitivity of simulated wet deposition to emission speciation and redox species concentration is non‐linear and varies by region. In regions with low wet deposition (5–15 μg m−2 yr−1), emission speciation and chemistry show comparable influence, whereas in regions with high wet deposition (15–30 μg m−2 yr−1), emission speciation shows greater influence than chemistry. The interregional differences in sensitivity suggest that different pathways control total wet deposition for different regions. While in our previous study we evaluated the modeling system against observations, the sensitivity studies described in this paper enabled us to obtain new insights on atmospheric mercury by focusing on the dynamics of the system, i.e., response of the system to variation in its inputs. This analysis is essential before model‐simulated results are used to investigate source‐receptor relationships. Our findings also indicate that there is a critical need to get additional data on mercury speciation of major emission sources.

Dry and wet deposition of mercury near a chlor-alkali plant

The dry and wet deposition near a Finnish chlor-alkali plant was estimated by using the moss-bag technique. The estimated net deposition was 130 ng g −1 per month or 480 μg m −2 per year. Two-thirds of the deposition was dry and one-third wet. The results emphasize the importance of the direct uptake of atmospheric mercury by vegetation.

Trends in atmospheric mercury concentrations at the summit of the Wank mountain, Southern Germany

Total gaseous mercury (TGM) has been monitored at the summit of the Wank mountain (1780 m a.s.l.) in the Bavarian Alps since March 1990. A statistical analysis of the data set until May 1996 consisting of 1670 individual TGM measurements shows a linear decrease of 0.169 ± 0.009 ng Hg m −3 yr −1, i.e. about 7% per year. The seasonal variation shows maximum TGM concentrations in March and minima in October–December. The frequency of occurrence of extremely high TGM concentrations and the amplitude of the seasonal variation decreased over the observation time. The observed decrease of the TGM concentration is in agreement with measurements in Scandinavia, indicating that the measurements at Wank are representative for the region of central and northern Europe. The decrease in TGM concentration of 23.3% between 1990 and 1994 was consistent with decreases of 20.4 and 21.2%, respectively, observed by us over the northern and the southern Atlantic Ocean. This and the observation of a decreasing trend in mercury wet deposition in the U.S.A. indicate the global significance of the TGM trends observed in Europe. Several causes may add up, but this 45% change in TGM concentrations observed over the period of 6 years cannot be plausibly explained without a substantial decrease of anthropogenic mercury emissions on both regional and global scales. Such decrease, however, is difficult to reconcile with most of the current anthropogenic emission inventories. This points to possible gaps in our understanding of the anthropogenic emission processes.

Simulation of the regional atmospheric transport and fate of mercury using a comprehensive eulerian model

This paper describes the development, testing and evaluation of a comprehensive mercury simulation model. The model was developed by starting with an existing model that simulates the sulfur/NO x/VOC system and then substituting modules specific to mercury (e.g. chemistry and scavenging). The transport and fate of mercury emissions in the contiguous United States was simulated with the mercury simulation model. We first tested the model by simulating the sulfur system using emissions from the 1990 U.S. EPA criteria pollutants inventory. This testing provided a measure of the uncertainties in the meteorological input data (e.g. gridded wind, cloud and precipitation fields) and model parameterizations (e.g. transport:) that are common to both the sulfur and mercury systems. The mercury simulation model was then evaluated by comparing model estimates of annual average concentrations and wet deposition amounts of mercury against published measurement data. The mercury evaluation showed that the model captured the range of observed values in most regions where observations were available. Moreover, observed spatial gradients in mercury wet deposition amounts and ambient concentrations were also seen in the model results. For the scenario considered here, the simulation results lead to an annual mercury wet deposition amount that is roughly twice the estimated annual dry deposition amount, for most regions of the modeling domain.

Atmospheric deposition of toxics onto Massachusetts Bay—I. Metals

Wet and dry atmospheric deposition of toxic metals was measured at biweekly intervals for one year, from i5 September i992 to i6 September i993 at two sites on Massachusetts Bay, Nahant, near Boston and Truro, near the tip of Cape Cod. Wet and dry deposition was measured using a conventional wet/dry collector, except that the dry bucket contained a layer of water in order to simulate the uptake of dry deposition onto a water surface. In addition, at Nahant, a dichotomous particle collector was used to measure metal concentrations on particles. Analytical methods were INAA and ICP-MS. Generally, dry deposition of metals was greater at Nahant than at Truro, and wet deposition was greater or equal at Truro than at Nahant. Averaging results from the two sites, the following deposition rates (wet + dry) were obtained for the Bay in μg m −2 yr −1: Al i02000, As i32, Cd 405, Co 58, Cr 2700, Cu 3500, Fe 140,000, Mn 4420, Ni 7200, Pb 2700, Sb i60, Se 264, Zn 7800. Preliminary results are also given for mercury wet deposition, which was measured for 6 weekly periods in the fall of 1993.

Wet deposition of mercury and ambient mercury concentrations at a site in the Lake Champlain basin

The “Great Waters” program, established in the 1990 Clean Air Act Amendments, mandated that atmospheric deposition of hazardous air pollutants to Lake Champlain (including Hg) be assessed. An assessment of the magnitude and seasonal variation of atmospheric Hg deposition in the Lake Champlain basin was initiated in December 1992 with one year of event precipitation collection, as well as collection of vapor and particle phase Hg in ambient air. Samples were collected at the Vermont Monitoring Cooperative air monitoring site at the Proctor Maple Research Center in Underhill Center, VT. The average volume-weighted concentration for Hg in precipitation was 8.3 ng/L for the sampling year and the average amount of Hg deposited with each precipitation event was 0.069 μg/m2. The total amount of Hg deposited through precipitation during 1993 was 9.26 μg/m2/yr. A seasonal pattern for Hg in precipitation was evident, with increased concentrations and deposition during spring and summer months. Meteorological analysis indicated the highest levels of Hg in precipitation were associated with regional transport from the south regardless of season, and with transport from the west, southwest and northwest during spring and summer months. Concentrations of ambient vapor phase Hg were typical of rural locations and consistent across seasons. Ambient particulate Hg concentrations averaged 11 pg/m3 with highest concentrations during the winter months.

Wet deposition of mercury and methylmercury from the atmosphere

The wet deposition of mercury and methylmercury was monitored for a period of 1 year at selected areas in the Federal Republic of Germany. These areas represented an industrial zone, an urban area, a rural area close to the industrial zone and other rural areas. The wet deposition of mercury was very much dependent on the collection area; the wet deposition of methylmercury (MM) was not area dependent. Maximum mercury was found as follows: industrial area > urban area > rural area close to the industrial zone > other rural areas. Methylmercury concentrations at all areas were almost uniform within analytical error. Methylmercury as a percentage of total mercury was 5–6% for rural areas and decreased to < 1% for industrial areas. Wet deposition of mercury increased in summer. Based on the experimental data the present burdens caused by the wet deposition of mercury and methylmercury are evaluated.