Mercury Deposition Network Research Articles

대기 중 수은의 습식 침적 평가: 소양호를 중심으로

The important source of the mercury in water-column is the influx of atmosphere mercury, via dry and wet deposition. In this study, wet deposition of mercury was estimated to be during 15 months at the Lake Soyang, which is a little higher than those observed in the several rural US Mercury Deposition Network (MDN) sites with similar precipitation depth. The mercury concentration in precipitation did not show a positive correlation with atmospheric RGM (reactive gaseous mercury) concentration, while maintaining good correlation with atmospheric at Soyang Dam. This result suggests that the contribution of particulate Hg to the total Hg wet deposition should be more significant than that of RGM. In this study, both precipitation depth and precipitation type affected the amount of wet deposition and the concurrent mercury levels in precipitation. There was generally an inverse relationship between precipitation depth and Hg concentration in precipitation. Precipitation type was another factor that exerted controls on the Hg concentration in precipitation. As a result, the highest concentration of Hg was observed in snow, followed by in mixture (snow+rain) and in rain.

Modelling Mercury Deposition Through Latent Space–Time Processes

This paper provides a space-time process model for total wet mercury deposition. Key methodological features introduced include direct modeling of deposition rather than of expected deposition, the utilization of precipitation information (there is no deposition without precipitation) without having to construct a precipitation model, and the handling of point masses at 0 in the distributions of both precipitation and deposition. The result is a specification that enables spatial interpolation and temporal prediction of deposition as well as aggregation in space or time to see patterns and trends in deposition.We use weekly deposition monitoring data from the NADP/MDN (National Atmospheric Deposition Program/Mercury Deposition Network) for 2003 restricted to the eastern U.S. and Canada. Our spatio-temporal hierarchical model allows us to interpolate to arbitrary locations and, hence, to an arbitrary grid, enabling weekly deposition surfaces (with associated uncertainties) for this region. It also allows us to aggregate weekly depositions at coarser, quarterly and annual, temporal levels.

A comparison of winter mercury accumulation at forested and no-canopy sites measured with different snow sampling techniques

Atmospheric mercury (Hg) is delivered to ecosystems via rain, snow, cloud/fog, and dry deposition. The importance of snow, especially snow that has passed through the forest canopy (throughfall), in delivering Hg to terrestrial ecosystems has received little attention in the literature. The snowpack is a dynamic system that links atmospheric deposition and ecosystem cycling through deposition and emission of deposited Hg. To examine the magnitude of Hg delivery via snowfall, and to illuminate processes affecting Hg flux to catchments during winter (cold season), Hg in snow in no-canopy areas and under forest canopies measured with four collection methods were compared: (1) Hg in wet precipitation as measured by the Mercury Deposition Network (MDN) for the site in Acadia National Park, Maine, USA, (2) event throughfall (collected after snowfall cessation for accumulations of >8 cm), (3) season-long throughfall collected using the same apparatus for event sampling but deployed for the entire cold season, and (4) snowpack sampling. Estimates (mean ± SE) of Hg deposition using these methods during the 91-day cold season in 2004–2005 at conifer sites showed that season-long throughfall Hg flux (1.80 μg/m2) < snowpack Hg (2.38 ± 0.68 μg/m2) < event throughfall flux (5.63 ± 0.38 μg/m2). Mercury deposition at the MDN site (0.91 μg/m2) was similar to that measured at other no-canopy sites in the area using the other methods, but was 3.4 times less than was measured under conifer canopies using the event sampling regime. This indicates that snow accumulated under the forest canopy received Hg from the overstory or exhibited less re-emission of Hg deposited in snow relative to open areas. The soil surface of field-scale plots were sprayed with a natural rain water sample that contained an Hg tracer (202Hg) just prior to the first snowfall to explore whether some snowpack Hg might be explained from soil emissions. The appearance of the 202Hg tracer in the snowpack (0–64% of the total Hg mass in the snowpack) suggests that movement of Hg from the soil into the snowpack is possible. However, as with any tracer study the 202Hg tracer may not precisely represent the reactivity and mobility of natural Hg in soils.

Scientific uncertainties in atmospheric mercury models III: Boundary and initial conditions, model grid resolution, and Hg(II) reduction mechanism

In this study, the model response in terms of simulated mercury concentration and deposition to boundary condition (BC), initial condition (IC), model grid resolution (12 km versus 36 km), and two alternative Hg(II) reduction mechanisms, was investigated. The model response to the change of gaseous elemental mercury (GEM) concentration from 0 to 2 ng m −3 in IC/BC is found to be very linear ( r 2>0.99) based on the results of sensitivity simulations in July 2001. An increase of 1 ng m −3 of GEM in BC resulted in an increase of 0.81 ng m −3 in the monthly average of total mercury concentration, and 1270 ng m −2 in the monthly total deposition. IC has similar but weaker effects compared to those of BC. An increase of 1 ng m −3 of GEM in IC resulted in an increase of 0.14 ng m −3 in the monthly average of total mercury concentration, and 250 ng m −2 in the monthly total deposition. Varying reactive gaseous mercury (RGM) or particulate mercury (PHg) in BC/IC has much less significant impact. Simulation results at different grid resolutions show good agreement (slope=0.950–1.026, r=0.816–0.973) in mercury concentration, dry deposition, and total deposition. The agreement in wet deposition is somewhat weaker (slope=0.770–0.794, r=0.685–0.892) due to the difference in emission dilution and simulated precipitation that subsequently change reaction rates in the aqueous phase. Replacing the aqueous Hg(II)-HO 2 reduction by either RGM reduction by CO (5×10 −18 cm 3 molecule −1 s −1) or photoreduction of RGM (1×10 −5 s −1) gives significantly better model agreement with the wet deposition measured by Mercury Deposition Network (MDN). Possible ranges of the reduction rates are estimated based on model sensitivity results. The kinetic estimate requires further verification by laboratory studies.

Regional precipitation mercury trends in the eastern USA, 1998–2005: Declines in the Northeast and Midwest, no trend in the Southeast

Mercury emissions in the USA declined between the 1990s and the beginning of this decade, largely due to the closure of municipal and medical waste incinerators. Declines in emissions have been greater in the Northeastern (NE) than the Midwestern (MW), and Southeastern (SE) regions of the eastern USA. During this time, global emissions of mercury have declined in Europe but have not declined in Asia and Africa. We have examined the patterns and trends in annual volume-weighted mean precipitation concentration for 33 Mercury Deposition Network (MDN) sites in the eastern USA, for the period 1998–2005. Individual linear regressions indicate that, 11 of 12 sites in the NE and all nine sites in the MW show declining patterns in mercury concentration, but only nine of these 21 sites show statistically significant downward trends ( p<0.10). For the SE, seven of 12 sites show a decreasing pattern, but only two sites show significant downward trends ( p<0.10). Random coefficient models were used to test the trends in mercury concentration for each of the three regions as a whole. These results for the NE and the MW are statistically significant ( p<0.01), and show annual declines of −1.70±0.51% (S.E.) per year, and −3.52±0.74% per year for the NE and MW, respectively. The SE region as a whole shows no significant trend in mercury concentration during the same period. Different mercury transformation and deposition processes in the SE may account for these results. A comprehensive mercury emissions record was not available for the same 1998–2005 time period as the precipitation concentration analysis. Therefore, while the empirical relation between changing regional mercury emissions and changing precipitation mercury concentrations is suggestive, it cannot be confidently assessed at this time.

Speciation of atmospheric mercury at two sites in northern Nevada, USA

Gaseous elemental mercury (Hg 0), reactive gaseous mercury (RGM), and mercury bound to particles (Hg p) were measured during seasonal 1- or 2-week data collection campaigns at two Mercury Deposition Network sites (NV02 and NV99) in northern Nevada, USA. The sites are rural but are located in an area of diverse natural and anthropogenic mercury sources that include undisturbed and mining mercury-disturbed enriched substrates, coal-fired power plants, ore processing facilities, and industrial facilities. Concentrations of Hg 0 averaged over all campaigns were 3.0±1.7 ng m −3 at NV02 and 2.5±3.1 ng m −3 at NV99, higher than has been reported for other rural sites. Hg 0 concentrations at the sites were found to be influenced by both local substrate emission and transport from regional source areas. Concentrations of RGM and Hg p were within ranges reported for other rural sites (13±18 and 9±7 pg m −3 at NV02, 7±8 and 13±12 pg m −3 at NV99, respectively). Mercury wet deposition rates measured over 3 years (2003–2005) were similar to other sites in the arid West (3.0±0.7 μg m −2 yr −1 at NV02, 3.9±0.4 μg m −2 yr −1 at NV99).

Development and Application of a Multipollutant Model for Atmospheric Mercury Deposition

Abstract A multipollutant model, the Community Multiscale Air Quality model paired with the Model of Aerosol Dynamics, Reaction, Ionization, and Dissolution (CMAQ-MADRID), is extended to include a comprehensive treatment of mercury processes and is applied to the simulation of the atmospheric deposition of sulfate and mercury over the United States during 1996. Model performance is evaluated first by comparison with annual sulfate wet deposition data from the National Atmospheric Deposition Program’s National Trends Network; the coefficient of determination r 2 is 0.77, and the model normalized error and bias are 53% and −8%, respectively. When actual precipitation data are used to scale the deposition fluxes, r 2 improves to 0.91 and the error and bias change to 42% and −41%, respectively. The scaled results underscore a tendency of the model to underestimate sulfate wet deposition. Model performance for mercury wet deposition is then evaluated by comparison with data from the Mercury Deposition Network. For annual mercury wet deposition, r 2 is 0.28 and the normalized error and bias are 81% and 73%, respectively, when the modeled precipitation data are used. Model performance improves when actual precipitation data are used to scale deposition fluxes: r 2 increases to 0.41 and the error and bias decrease to 40% and 29%, respectively. The model reproduces the spatial pattern of sulfate wet deposition adequately with an increasing gradient from the upper Midwest to the Northeast, that is, from upwind to downwind of large sulfur dioxide sources in the Ohio River Valley. However, the model tends to overestimate mercury wet deposition in the Northeast downwind of these sources that also emit significant amounts of mercury. This “Pennsylvania anomaly” may be due to a partial misrepresentation of the mercury reduction–oxidation cycle, uncertainties in the dry deposition of divalent gaseous mercury HgII, incorrect speciation of mercury emissions, and/or uncharacterized emissions in the upper Midwest.

Trend, seasonal and multivariate analysis study of total gaseous mercury data from the Canadian atmospheric mercury measurement network (CAMNet)

Long-term monitoring data of total gaseous mercury (TGM) concentrations from the Canadian Atmospheric Mercury Measurement Network (CAMNet) were analysed for temporal trends, seasonality and comparability within the network and compared to other network and model results. Data collected from 11 Canadian measurement sites between 1995 and 2005 were analysed. Sites within CAMNet were characterized by principle component analysis (PCA) into four main categories. For the first time since automated TGM measurements have been made within CAMNet, this paper reveals statistically significant decreasing TGM concentrations from rural locations in Canada during this time period. The largest declines were observed close to the urban areas of Toronto and Montreal, where levels fell by 17% at Point Petre, and 13% at St. Anicet, respectively. Many of the TGM changes are comparable with the overall trends observed in total mercury concentrations in precipitation, for similar time periods, at co-located or nearby National Atmospheric Deposition programme's Mercury Deposition Network (NADP-MDN) sites. The results show that these changes are mostly driven by local or regional changes in mercury emissions. Other sites within CAMNet reflect reported changes in hemispherical global background concentrations of airborne mercury, where slight decreases or no statistically significant trend in TGM concentrations exist over the same time period.

Estimation of Dry Deposition of Atmospheric Mercury in Nevada by Direct and Indirect Methods

Atmospheric models and limited measurements indicate that dry deposition of atmospheric mercury is an important process by which mercury is input to ecosystems. To begin to fill the measurement data gap, multiple methods were used simultaneously during seasonal campaigns conducted in 2005 and 2006 to estimate dry deposition of atmospheric mercury at two Mercury Deposition Network (MDN) sites in rural Nevada and in Reno, Nevada. Gaseous elemental mercury (Hg0), reactive gaseous mercury (RGM), and particulate-bound mercury (Hgp) concentrations were measured using Tekran 2537A/1130/ 1135 systems. These speciated measurements were combined with on-site meteorological measurements to estimate depositional fluxes of RGM and Hgp using dry deposition models. Modeled fluxes were compared with more direct measurements obtained using polysulfone cation-exchange membranes and foliar surfaces. Dynamic flux chambers were used to measure soil mercury exchange. RGM concentrations were higher during warmer months at all sites, leading to seasonal variation in the modeled importance of RGM as a component of total depositional load. The ratio of dry to wet deposition was between 10 and 90%, and varied with season and with the methods used for dry deposition approximations. This work illustrates the variability of mercury dry deposition with location and time and highlights the need for direct dry deposition measurements.

Modeling of mercury emission, transport and deposition in North America

Most studies on the atmospheric behaviour of mercury in North America have excluded a detailed treatment of natural mercury emissions. The objective of this work is to report a detailed simulation of the atmospheric mercury in a domain that covers a significant part of North America and includes not only anthropogenic mercury emissions but also those from natural sources including vegetation, soil and water. The simulations were done using a natural mercury emission model coupled with the US EPA's SMOKE/CMAQ modelling system. The domain contained 132×90 grid cells at a resolution of 36 km, covering the continental United States, and major parts of Canada and Mexico. The simulation was carried out for 2002, using boundary conditions from a global mercury model. Estimated total natural mercury emission in the domain was 230 tonnes (1 tonne=1000 kg) and the ratio of natural to anthropogenic emissions varied from 0.7 in January to 3.2 in July. Average total gaseous mercury (TGM) concentration ranged between 1 and 4 ng m −3. Good agreement was found between the modelled results and measurements at three Ontario sites for ambient mercury concentrations, and at 72 mercury deposition network sites in the domain for wet deposition. The correlation coefficient between the simulated and the measured values of the daily average TGM at three monitoring sites varied between 0.48 and 0.64. When natural emissions were omitted, the correlation coefficients dropped to between 0.15 and 0.40. About 335 tonnes of mercury were deposited in the domain during the simulation period but overall, it acted as a net source of mercury and contributed about 21 tonnes to the global pool. The net deposition of mercury to the Great Lakes was estimated to be about 2.4 tonnes. The estimated deposition values were similar to those reported by other researchers.

Predicting mercury wet deposition in Florida: A simple approach

Atmospheric mercury deposition is currently simulated using complex models that incorporate known transport and transformation processes. Though comprehensive, significant errors still exist between simulated and measured Mercury Deposition Network (MDN) data. The goal of this work was to develop a simpler approach to predict mercury deposition. Weekly precipitation sampling in Orlando, FL was conducted from September 2003 and presently continues. Rainfall and mercury deposition data were gathered from this site and 7 others located in and around Florida, to investigate spatial and seasonal patterns. Approximately 80% of Florida's rainfall and mercury deposition occur during the wet season. Regional wet and dry season equations were developed to predict mercury deposition from rainfall depth. A positive linear relationship was observed between rainfall depth and mercury deposition ( R 2 = 0.80 ). Model results were validated with MDN measurements at the Orlando site. This tool can be applied to predict mercury deposition at any location in Florida using local rainfall data.

IDENTIFICATION OF POSSIBLE MERCURY SOURCES AND ESTIMATION OF MERCURY WET DEPOSITION FLUX IN LAKE ONTARIO FROM LAKE ONTARIO ATMOSPHERIC DEPOSITION STUDY (LOADS)

Total gas phase mercury (TGM) concentrations and event wet-only precipitation for Hg were collected for nine months (from April, 2002 to Dec., 2002) at Sterling, NY on the shoreline of Lake Ontario. TGM concentrations measured in this study () were in somewhat high range compared to other background sites. Using simplified quantitative transport bias analysis (SQTBA) possible sources affecting high Hg concentration in Sterling was identified, and they are coal-fired power plants located in southern NY and Pennsylvania. Wet deposition measured at Mercury Deposition Network (MDN) sites including Pt. Petre and Egbert, ON were compared with data obtained at the Sterling to estimate the total mercury wet deposition flux to Lake Ontario. The wet deposition flux was calculated to be the highest at the Sterling site ( from April, 2002 to Dec. 2002) and the lowest at the Egbert (), due to the both the difference in precipitation depth and Hg concentration in the precipitation. The deposition measured at the Sterling site is similar to Lake Michigan deposition of (converted for ninth months) measured for Lake Michigan Mass Balance Study (LMMBS).

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.

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 .

Contributions of global and regional sources to mercury deposition in New York State

A modeling system that includes a global chemical transport model (CTM) and a nested continental CTM (TEAM) was used to simulate the atmospheric transport, transformations and deposition of mercury (Hg). Three scenarios were used: (1) a nominal scenario, (2) a scenario conducive to local deposition and (3) a scenario conducive to long-range transport. Deposition fluxes of Hg were analyzed at three receptor locations in New York State. For the nominal scenario, the anthropogenic emission sources (including re-emission of deposited Hg) in New York State, the rest of the contiguous United States, Asia, Europe, and Canada contributed 11–21, 25–49, 13–19, 5–7, and 2–5%, respectively to total Hg deposition at these three receptors. Natural sources contributed 16–24%. The results from the local deposition and long-range transport scenarios varied only slightly from these results. However, there are still uncertainties in our understanding of the atmospheric chemistry of Hg that are likely to affect these estimates of local, regional and global contributions. Comparison of model simulation results with data from the Mercury Deposition Network suggests that local and regional contributions may currently be overestimated.

Multiscale modeling of the atmospheric fate and transport of mercury

A numerical simulation of the atmospheric fate and transport of mercury (Hg) was conducted using a multiscale approach. Two different spatial scales were used to simulate (1) the global cycling of atmospheric Hg and (2) the atmospheric deposition of Hg in potentially sensitive areas. The global simulation was conducted using an updated version of our global Hg chemical transport model (CTM). The imbedded continental simulation was conducted using an updated version of the regional/continental CTM, TEAM. Simulations were conducted using 1998 meteorology and 1998/1999 emission inventories. Model simulation results show improved performance compared to earlier simulations. For example, the global simulation shows background concentrations of Hg species, interhemispheric gradients, and vertical gradients that are consistent with available measurements. The comparison of simulated Hg wet deposition fluxes with data from the Mercury Deposition Network in the United States shows a coefficient of determination (r2) of 0.75, little bias (−3%), and an average gross error of 21%. The major remaining sources of uncertainties, which include speciation of Hg emissions, Hg atmospheric chemistry, and dry and wet deposition processes for Hg species, are discussed.

The need for integrated linkages and long-term monitoring of mercury in Canada.

A nation-wide ecosystem science network for Canada was formed in 1994. At that time, mercury was a re-emerging issue in Canada and the Coordinating Office for the network sought collaboration to assess the issue. The key mechanisms by which the network has added value in addressing this issue are: 1) Information Dissemination, the network has organised, facilitated and co-hosted a number of regional. national and international mercury events (meetings, conferences and workshops) which have served to bring the expertise together, the network also disseminates information on it's web page. and the Coordinating Office hosts an annual National Science Conference: 2) Collaborative Mercury Monitoring, network partners advocated the need for a single hemispheric mercury network which resulted in the development of a compatible Canada-U.S. mercury deposition network, which may also be expanded into Mexico, and 3) Environmental Reporting, the network has collaborated with others to report on current mercury findings through initiatives such as the 1998 Northeast States and Eastern Canadian Mercury Study, a 1999 Mercury Case Study and is presently a partner in the University of Quebec's proposal to form a Collaborative Mercury Ecosystem Research Network in Canada.

Workshop on sampling mercury in precipitation for the national atmospheric deposition program

Several actions have been undertaken within the National Atmospheric Deposition Program (NADP) to implement a regional mercury deposition network. This paper reports on the general findings of a National Atmospheric Deposition Program workshop on sampling mercury in precipitation, which has led to several conclusions important to the design of a regional sampling network for mercury.

Field tests for a regional mercury deposition network—sampling design and preliminary test results

A number of actions have been undertaken within the National Atmospheric Deposition Program (NADP) to implement a regional mercury deposition network. This paper describes a field test designed to evaluate a collector design and protocol for implementation within a new Hg network. The collector chosen for evaluation is a “dual-orifice” collector, designed to sample precipitation for mercury and other metals simultaneously. The method chosen for Hg analysis was cold vapour atomic fluorescence spectroscopy (CVAFS). The weekly precipitation Hg concentrations range between 4.29 and 17.88 ng ℓ −1, with a volume-weighted mean of 10 ng ℓ −1 comparable to those reported in other ongoing studies in North America and Europe. Calculated deposition flux ranges from 43 to 358 ng m −2 week −1, with a mean of 186 ng m −2 week −1.