Mercury Wet Deposition Research Articles

Unexpectedly high wet mercury deposition observed in the Yarlung Tsangpo Grand canyon

Situated in the south edge of the Tibetan Plateau, the Himalayas is expected to receive direct anthropogenic Hg perturbations from South Asia, yet the measurements of atmospheric Hg deposition in the Himalayan region remain scarce. Here we report wet Hg deposition measured in the Yarlung Tsangpo Grand Canyon of the Eastern Himalayas, which is the deepest and longest canyon on earth. The precipitation Hg concentration (56.3 ng L−1) and wet Hg deposition flux (84.7 μg m−2 yr−1) from the Motuo station were observed among the highest ever reported for the Tibetan Plateau. Together with analysis of principal component suggesting Hg was mainly clustered with anthropogenic ions and backward trajectories indicating 88.8% of air masses came from South Asia, our results show that transboudary pollution influences from South Asia could be largely responsible for the unexpectedly high levels of wet Hg deposition. Moreover, the wet Hg flux measurements (84.7 μg m−2 yr−1) are found an order of magnitude (∼13 times) higher than the GEOS-Chem estimates (6.8 μg m−2 yr−1), most likely due to the underestimation of transboundary Hg pollution influence by this model. Our study has important implications for better understanding Hg dynamics and verifying atmospheric Hg models in the Tibetan Plateau and Himalayas region.

Atmospheric wet deposition of mercury in urban Jinan, eastern China: Speciation, scavenging process and potential sources

Understanding the speciation and related influence factors of Hg in wet deposition is important to predict the fate and transport of mercury in the atmosphere. In this study, event-based samples of rainwater were collected for one year in Jinan, a northern city in eastern China. The volume-weighted mean concentration of total mercury (THg) in rainwater was 34.8 ng L−1, comparable to levels in some inland cities in China and were significantly higher than those in North America, Korea and Japan. Most of the Hg in rainwater was associated with particulates, accounted for 15.2–92.9% of THg with a mean of 66.9%, which might be attributed to the scavenging effects of high particulate-bound mercury concentrations in ambient air in urban Jinan. Dissolved mercury (DHg) accounted for 33.1% of THg, in which Hg(OH)2, HgClOH, HgCl2 and Hg(NH3)22+ are the dominant species based on the chemical equilibrium modeling simulations. THg concentrations in rainwater decreased as the rainfall amount increased owing to the dilution effect and 5 mm rainfall might be a threshold for the full wash-out capability of atmospheric Hg. For a continuous rain event, the proportion of DHg in THg could increase from 7.1% to 84.8% with the rainfall processing, especially for the species of HgClOH and HgCl2 under the influence of rainwater pH. Positive matrix factorization (PMF) analysis suggested that the major sources of Hg in rainwater were combustion emissions, marine sources, industrial emissions, as well as complexation process, which contributed to 51.4%, 24.7%, 12.2%, and 11.7% of the THg, respectively. For the specific species, the main sources varied with different Hg species, in which combustion emissions contributed one third to one half of each species sum to particulate mercury (PHg), HgClOH, HgCl2, HgBrOH and HgBrCl followed by marine sources and industrial emissions. Cluster analysis of backward trajectories revealed that polluted air masses, transported from southeast Shandong, Anhui and Jiangsu Provinces, as well as Beijing-Tianjin-Hebei region, contributed to high Hg concentration in rainwater in Jinan.

Modeling the high-mercury wet deposition in the southeastern US with WRF-GC-Hg v1.0

Abstract. High-mercury wet deposition in the southeastern United States has been noticed for many years. Previous studies came up with a theory that it was associated with high-altitude divalent mercury scavenged by convective precipitation. Given the coarse resolution of previous models (e.g., GEOS-Chem), this theory is still not fully tested. Here we employed a newly developed WRF-GEOS-Chem (WRF-GC; WRF: Weather Research Forecasting) model implemented with mercury simulation (WRF-GC-Hg v1.0). We conduct extensive model benchmarking by comparing WRF-GC with different resolutions (from 50 to 25 km) to GEOS-Chem output (4∘ × 5∘) and data from the Mercury Deposition Network (MDN) in July–September 2013. The comparison of mercury wet deposition from two models presents high-mercury wet deposition in the southeastern United States. We divided simulation results by heights (2, 4, 6, 8 km), different types of precipitation (large-scale and convective), and combinations of these two variations together and find most mercury wet deposition concentrates on higher level and is caused by convective precipitation. Therefore, we conclude that it is the deep convection that caused enhanced mercury wet deposition in the southeastern United States.

Mercury wet depositions study during plum rain, regular precipitations and near typhoon periods

This study analyzed the rainwater collected in Central Taiwan during the near typhoon period. Mercury (Hg) was analyzed and the Hg volume weighted mean concentrations (VWM) and wet depositions were calculated during the near typhoon period. In addition, the Hg wet depositions, VWM and precipitation values obtained were compared with Plum rain and regular precipitation periods. The relationship between wet Hg depositions, VWM and precipitations were also discussed. Wet Hg depositions, VWM and precipitations were also compared with the precipitation collected from other parts of the world during 2009 to 2021. The results indicated that the precipitations, VWM and wet Hg depositions in the near typhoon period were 152.5 mm, 0.82 ng/L, and 0.29 μg/m2, respectively. The Hg precipitation ratio values of this study to the plum rain and regular precipitation periods were 3.70 and 6.63, respectively. The Hg VWM ratios values of this study to the plum rain and regular precipitation periods were 12,852.56 and 1.56, respectively. Moreover, the wet Hg deposition ratios values of this study to the plum rain and regular precipitation periods (near typhoon period) were 105.97 and 9.90, respectively. The results further indicated that the Hg VWM and wet depositions obtained in the near typhoon period showed the lowest values when compared with plum rain and regular precipitations periods. Compared with Hg(p) VWM and Fw values obtained from plum season, regular precipitation, this study (typhoon period) demonstrated it has the average lowest VWM and Fw values among these three sampling periods. The correlation coefficient of precipitation and the mercury wet deposition was 0.72051 which was significant in this study. The correlation coefficient for the VWM of mercury was 0.0826 which displayed insignificant relationship in this study. Finally, when comparing the Hg VWM, wet deposition and precipitation values from various studies, the results further indicated that the near typhoon period has the lowest average Hg VWM, wet deposition and precipitation values.

Contrasting changes in long-term wet mercury deposition and socioeconomic development in the largest city of Tibet

Information about the long-term trends of wet mercury (Hg) deposition is important for assessing the impact of atmospheric pollution on environmental health. As the most populated and capital city of Tibet, Lhasa is isolated far away from the heavily-polluted urban clusters in China. In this study, a 10-year observation was conducted in Lhasa to establish the long-term trend of wet Hg deposition and investigate the possible causes of this variation trend. Our study showed no significant increase in wet Hg deposition while Lhasa has achieved rapid population and economic growth during the study period. The contrasting changes in long-term wet Hg deposition and socioeconomic development (e.g., GDP growth) could be greatly attributed to the efforts in preventing and controlling air pollution at regional and local levels. This trend in Lhasa differs greatly from those observed by a rapid increase of Hg trend in the remote areas of the Tibetan Plateau. Our findings indicate that the remote cryospheric areas over the Tibetan Plateau are prone to be affected by transboundary Hg pollution, and more attention should be paid to its environmental and health effects for future study.

Wet Deposition of Mercury and Dissolved Organic Carbon during Pre-Monsoon and Monsoon Periods at Sitapuri Site in Delhi (India)

This rainwater chemistry study was carried out during monsoon and pre-monsoon seasons in 2018. The rainwater samples were collected in the residential area of Sitapuri which is situated the southwest zone of city Delhi. The rainwater samples were collected with the help of the funnel and bottle assembly on event basis. To refrain any contamination from the ground, the assembly was mounted at 5m above the ground level on a terrace. The assembly was always installed on the onset of rain and retrieved soon after the rain stopped. The collected samples were filtered. The samples were analyzed for Mercury (Hg0), Total Nitrogen (TN) and Dissolved Organic Carbon (DOC). The Hg(o) determination was done using Differential Pulse Anodic Stripping Voltammetry through standard addition methods and DOC species and TN species were determined using DOC/TN analyzer (Shimadzu model LCPH/CPN). The average concentration of Hg0 was recorded as 54.9 μg/l, while that of DOC and TN as 160.2 mg/l and 12.6 mg/l respectively. The study indicated that Hg0 and DOC were not contributed by common emission sources. Also, the study indicated that pre-monsoon air was more contaminated with Hg (0), TN and DOC as compared to the monsoon season.

Previously unaccounted atmospheric mercury deposition in a midlatitude deciduous forest

Mercury is toxic to wildlife and humans, and forests are thought to be a globally important sink for gaseous elemental mercury (GEM) deposition from the atmosphere. Yet there are currently no annual GEM deposition measurements over rural forests. Here we present measurements of ecosystem-atmosphere GEM exchange using tower-based micrometeorological methods in a midlatitude hardwood forest. We measured an annual GEM deposition of 25.1 µg ⋅ m-2 (95% CI: 23.2 to 26.7 1 µg ⋅ m-2), which is five times larger than wet deposition of mercury from the atmosphere. Our observed annual GEM deposition accounts for 76% of total atmospheric mercury deposition and also is three times greater than litterfall mercury deposition, which has previously been used as a proxy measure for GEM deposition in forests. Plant GEM uptake is the dominant driver for ecosystem GEM deposition based on seasonal and diel dynamics that show the forest GEM sink to be largest during active vegetation growing periods and middays, analogous to photosynthetic carbon dioxide assimilation. Soils and litter on the forest floor are additional GEM sinks throughout the year. Our study suggests that mercury loading to this forest was underestimated by a factor of about two and that global forests may constitute a much larger global GEM sink than currently proposed. The larger than anticipated forest GEM sink may explain the high mercury loads observed in soils across rural forests, which impair water quality and aquatic biota via watershed Hg export.

Hydrobiochemical balance of total mercury in a forest catchment area at former cinnabar mining locality

Abstract We studied the hydrobiochemical balance of total mercury (THg) in a forest ecosystem covering an area affected by mining activity in the past (14th – 18th cent.) in the Kremnické vrchy Mts. (central Slovakia). A reference plot was located in an undisturbed area very close to primeval forest of Badínsky prales natural reserve. We analysed THg in bulk precipitation, throughfall, litterfall, forest floor percolate, forest soil and assimilatory organs of tree species. Results pointed out to high wet mercury deposition at both plots (51 μg·m−2·yr−1 an area near a cinnabar mining (MP1) and 37 μg·m−2·yr−1, in a reference catchment area near the protected primary forest (MP2)) as well as high THg deposition by throughfall (74 μg·m−2·yr−1 and 51 μg·m−2·yr−1, respectively in MP1 and MP2). Litterfall does not represent the main THg flux into forest soil but together with throughfall doubles the THg input compared to open space deposition. Forest ecosystem has ability to capture atmospheric Hg and thus makes new sources of mercury inputs (throughfall and litterfall) into soil.

Long-Term Trends in Regional Wet Mercury Deposition and Lacustrine Mercury Concentrations in Four Lakes in Voyageurs National Park

Although anthropogenic mercury (Hg) releases to the environment have been substantially lowered in the United States and Canada since 1990, concerns remain for contamination in fish from remote lakes and rivers where atmospheric deposition is the predominant source of mercury. How have aquatic ecosystems responded? We report on one of the longest known multimedia data sets for mercury in atmospheric deposition: aqueous total mercury (THgaq), methylmercury (MeHgaq), and sulfate from epilimnetic lake-water samples from four lakes in Voyageurs National Park (VNP) in northern Minnesota; and total mercury (THg) in aquatic biota from the same lakes from 2001–2018. Wet Hg deposition at two regional Mercury Deposition Network sites (Fernberg and Marcell, Minnesota) decreased by an average of 22 percent from 1998–2018; much of the decreases occurred prior to 2009, with relatively flat trends since 2009. In the four VNP lakes, epilimnetic MeHgaq concentrations declined by an average of 44 percent and THgaq by an average of 27 percent. For the three lakes with long-term biomonitoring, temporal patterns in biotic THg concentrations were similar to patterns in MeHgaq concentrations; however, biotic THg concentrations declined significantly in only one lake. Epilimnetic MeHgaq may be responding both to a decline in atmospheric Hg deposition as well as a decline in sulfate deposition, which is an important driver of mercury methylation in the environment. Results from this case study suggest that regional- to continental-scale decreases in both mercury and sulfate emissions have benefitted aquatic resources, even in the face of global increases in mercury emissions.

Gaseous Elemental Mercury Concentrations along the Northern Gulf of Mexico Using Passive Air Sampling, with a Comparison to Active Sampling

Mercury is a toxic element that is dispersed globally through the atmosphere. Accurately measuring airborne mercury concentrations aids understanding of the pollutant’s sources, distribution, cycling, and trends. We deployed MerPAS® passive air samplers (PAS) for ~4 weeks during each season, from spring 2019 to winter 2020, to determine gaseous elemental mercury (GEM) levels at six locations along the northern Gulf of Mexico, where the pollutant is of particular concern due to high mercury wet deposition rates and high concentrations in local seafood. The objective was to (1) evaluate spatial and seasonal trends along the Mississippi and Alabama coast, and (2) compare active and passive sampling methods for GEM at Grand Bay National Estuarine Research Reserve, an Atmospheric Mercury Network site. We observed higher GEM levels (p < 0.05) in the winter (1.53 ± 0.03 ng m−3) compared to other seasons at all sites; with the general pattern being: winter > spring > summer ≈ fall. Average GEM levels (all deployment combined) were highest at Bay St. Louis (1.36 ± 0.05 ng m−3), the western-most site nearest the New Orleans metropolitan area, and lowest at Cedar Point (1.07 ± 0.09 ng m−3), a coastal marsh with extensive vegetation that can uptake GEM. The MerPAS units compared reasonably well with the established active monitoring system, but gave slightly lower concentrations, except in the winter when the two methods were statistically similar. Both the passive and active sampling methods showed the same seasonal trends and the difference between them for each season was <15%, acceptable for evaluating larger spatial and temporal trends. Overall, this work demonstrates that PASs can provide insight into GEM levels and the factors affecting them along coastal regions.

Mercury wet depositions study at suburban, agriculture and traffic sampling sites.

This study aimed to measure and discuss the relationship of ambient air precipitations with respect to mercury wet depositions at suburban, agriculture and traffic three characteristic sampling sites during the year of 2019. In addition, the mercury volume weighted mean concentrations (VWM) at three characteristic sampling sites were also calculated. Finally, the ambient mercury wet depositions data obtained in this study to various world sampling sites were also compared and discussed in this study. The results indicated that the average mercury wet depositions for suburban, agriculture and traffic areas were 0.62, 0.55 and 2.32ng/m2min, respectively. And the average mercury VWM values were 0.9, 0.72 and 1.85ng/m2min for suburban, agriculture and traffic sites, respectively. In addition, the highest VWM and wet depositions for mercury both occurred in March at traffic and suburban areas. And the mercury wet depositions displayed a declined trend when the month was moved from March to July at both traffic and suburban sampling sites. In addition, the relationship between wet depositions and precipitations was low to moderate correlated in traffic area, while the relationship between wet depositions and precipitations was insignificant at both suburban and agriculture areas. Moreover, the average highest mercury wet deposition occurred in Nepal when compared to the other world sites. In addition, the average value of mercury wet depositions in Nepal was about 17.23 times to that of data obtained in this study during the period of 2007-2019. Finally, the average highest VWM (ng/L) occurred in the China. In addition, the average value mercury VWM in China was about 14.82 times to that of data obtained in this study during the period of 2007-2019.

Long-Term Observations of Atmospheric Speciated Mercury at a Coastal Site in the Northern Gulf of Mexico during 2007–2018

Atmospheric mercury species (gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particulate-bound mercury (PBM)), trace pollutants (O3, SO2, CO, NO, NOY, and black carbon), and meteorological parameters have been continuously measured since 2007 at an Atmospheric Mercury Network (AMNet) site that is located on the northern coast of the Gulf of Mexico in Moss Point, Mississippi. For the data that were collected between 2007 and 2018, the average concentrations and standard deviations are 1.39 ± 0.22 ng m−3 for GEM, 5.1 ± 10.2 pg m−3 for GOM, 5.9 ± 13.0 pg m−3 for PBM, and 309 ± 407 ng m−2 wk−1 for mercury wet deposition, with interannual trends of −0.009 ng m−3 yr−1 for GEM, −0.36 pg m−3 yr−1 for GOM, 0.18 pg m−3 yr−1 for PBM, and 2.8 ng m−2 wk−1 yr−1 for mercury wet deposition. The diurnal variation of GEM shows lower concentrations in the early morning due to GEM depletion, likely due to plant uptake in high humidity events and slight elevation during the day, likely due to downward mixing to the surface of higher concentrations of GEM in the air aloft. The seasonal variation of GEM shows higher levels in winter and spring and lower levels in summer and fall. Diurnal variations of both GOM and PBM show broad peaks in the afternoon likely due to the photochemical oxidation of GEM. Seasonally, PBM measurements exhibit higher levels in winter and early spring and lower levels in summer with rising levels in fall, while GOM measurements show high levels in late spring/early summer and late fall and low levels in winter. The seasonal variation of mercury wet deposition shows higher values in summer and lower values in winter, due to larger rainfall amounts in summer than in winter. As expected, anticorrelation between mercury wet deposition and the sum of GOM and PBM, but positive correlation between mercury wet deposition and rainfall were observed. Correlation among GOM, ozone, and SO2 suggests possible different GOM sources: direct emissions and photochemical oxidation of GEM, with the possible influence of boundary layer dynamics and seasonal variability. This study indicates that the monitoring site experiences are impacted from local and regional mercury sources as well as large scale mercury cycling phenomena.

Mercury and trace metal wet deposition across five stations in Alaska: controlling factors, spatial patterns, and source regions

Abstract. A total of 1360 weeks of mercury (Hg) wet deposition data were collected by the state of Alaska Department of Environmental Conservation and the U.S. National Park Service across five stations spanning up to 8 years. Here, we analyze concentration patterns, source regions, and seasonal and annual Hg deposition loadings across these five sites in Alaska, along with auxiliary trace metals including Cr, Ni, As, and Pb. We found that Hg concentrations in precipitation at the two northernmost stations, Nome (64.5∘ N) along the coast of the Bering Sea and the inland site of Gates of the Arctic (66.9∘ N), were statistically higher (average of 5.3 and 5.5 ng L−1, respectively) than those at the two lowest-latitude sites, Kodiak Island (57.7∘ N, 2.7 ng L−1) and Glacier Bay (58.5∘ N, 2.6 ng L−1). These differences were largely explained by different precipitation regimes, with higher precipitation at the lower-latitude stations leading to dilution effects. The highest annual Hg deposition loads were consistently observed at Kodiak Island (4.80±1.04 µg m−2), while the lowest annual deposition was at Gates of the Arctic (2.11±0.67 µg m−2). Across all stations and collection years, annual precipitation strongly controlled annual Hg deposition, explaining 73 % of the variability in observed annual Hg deposition. The data further showed that annual Hg deposition loads across all five Alaska sites were consistently among the lowest in the United States, ranking in the lowest 1 % to 5 % of over 99 monitoring stations. Detailed back-trajectory analyses showed diffuse source regions for most Hg deposition sites suggesting largely global or regional Hg sources. One notable exception was Nome, where we found increased Hg contributions from the western Pacific Ocean downwind of East Asia. Analysis of other trace elements (As, Cr, Cu, Ni, Pb, Se, Zn) from Dutch Harbor, Nome, and Kodiak Island showed generally higher trace metal concentrations at the northern station Nome compared to Kodiak Island further to the south, with concentrations at Dutch Harbor falling in between. Across all sites, we find two distinct groups of correlating elements: Cr and Ni and As and Pb. We attribute these associations to possibly different source origins, whereby sources of Ni and Cr may be derived from crustal (e.g., dust) sources while As and Pb may include long-range transport of anthropogenic pollution. Hg was not strongly associated with either of these two groups.

Four-year Measurements of Wet Mercury Deposition at a Tropical Mountain Site in Central Taiwan

ABSTRACT Rainwater samples were collected between 2010 and 2013 at Lulin Atmospheric Background Station (LABS) to study the distribution and characteristics of wet mercury (Hg) deposition, and possible driving mechanisms. Sample Hg concentrations ranged from 0.8 to 35.1 ng L–1 with an overall volume-weighted mean (VWM) concentration of 9.2 ng L–1. Annual wet Hg deposition fluxes ranged between 24.4 and 48.9 µg m–2 with a mean value of 32.3 µg m–2. This mean annual wet flux was about 1.5–6.0 times the values measured at 15 sites in the U.S. and 4–16 times the values reported from mountain and high-elevation sites in China. Both rainwater Hg concentration and rainfall amount contributed to this geographical difference, but rainfall amount played a more important role. This indicated that tropical mountains in East and Southeast Asia, especially the windward maritime slopes with abundant rainfall, could be hot spots of wet Hg deposition. Wet Hg deposition flux was high in summer because of elevated rainwater Hg concentrations and high rainfall. The seasonal pattern of rainwater Hg concentrations was different from that of the East Asian air pollutant export, indicating other factors, e.g., rainfall type, were also influencing rainwater Hg concentrations. A clear difference in seasonal frequency distribution of rainfall types was observed, with rain events associated with the Pacific high pressure type (PH) occurring more frequently in summer months. PH rainfall type had the highest VWM Hg concentration (13.5 ng L–1), 2.3–6.2 ng L–1 greater than those of the other rainfall types. Because of intense surface heating under summer PH conditions, precipitation systems usually form locally due to strong convection, resulting in afternoon shower. Therefore, the elevated rainwater Hg levels in summer at LABS were likely due to the scavenging of free tropospheric gaseous oxidized Hg (GOM) by deep convection.

Primary effects of changes in meteorology vs. anthropogenic emissions on mercury wet deposition: A modeling study

In this study we investigated the respective contributions of changing meteorology and anthropogenic emissions to Hg wet deposition in New York State (NYS), which illustrated quantitatively how the variations in meteorological conditions modified the response of Hg wet deposition to anthropogenic emission reductions in NYS. A regional chemical transport model, CMAQ-newHg-Br (Ye et al., 2018), was employed driven by four sets of meteorological fields (2004, 2005, 2007, and 2010) and two anthropogenic emission inventories (NEI, 2005 and 2011). Four major findings emerged from this study. First, simulated Hg wet deposition flux in NYS was greatly affected by variation in meteorological conditions, ranging from a 91% decrease to a factor of 5 increase in monthly Hg wet deposition, whereas it hardly responded (2%) to a near doubling of emissions in the northeastern U.S. Second, the precipitation amount dominated interannual and seasonal variations of Hg wet deposition over all other meteorological variables, with total (= convective + non-convective) precipitation explained 60% of Hg wet deposition variance in an urban environment compared to convective precipitation alone explaining 65% in a rural area. Third, large-scale atmospheric circulation influenced regional transport greatly leading to out-of-state anthropogenic emissions explaining at least 80% of Hg wet deposition changes in a NYS urban environment. Fourth, higher Hg concentrations in precipitation and higher atmospheric reactive mercury concentrations in urban areas were related to calm conditions due likely to regional build-up of emissions, whereas in rural areas photochemical oxidation of gaseous elemental mercury was a more important source of reactive mercury. Solar radiation variance was found to explain 41–55% of the variance in simulated reactive mercury concentrations. Given that more than 95% of the US is rural lands and the majority of water bodies occur in rural areas, a realistic chemical mechanism for photochemical gaseous elemental mercury oxidation is paramount to accurate simulation of reactive mercury formation and Hg wet deposition in the US.

Mercury wet deposition and speciated mercury air concentrations at rural and urban sites across New York state: Temporal patterns, sources and scavenging coefficients

Measurements of ambient speciated mercury (Hg) concentrations and Hg wet deposition were made at two urban sites (Bronx, NY and Rochester, NY) and one rural site (Potsdam, NY) in New York State in 2013 and 2014 to: 1) determine the factors influencing Hg wet deposition concentrations, 2) identify the contribution of gaseous oxidized Hg (GOM) and particulate bound Hg (PBM) scavenging to Hg wet deposition concentrations, and 3) identify potential source areas associated with high concentration events. The Bronx had the highest mean gaseous elemental Hg (GEM) and GOM concentrations, Rochester had the highest mean PBM and the lowest GOM concentrations, and Potsdam had the lowest mean GEM and PBM concentrations. The annual volume weighted mean (VWM) Hg concentrations and Hg wet deposition fluxes in the Bronx, Rochester, and Potsdam were significantly different with mean values of 10.3 ± 8.16, 10.2 ± 9.06, and 5.07 ± 1.79 ngL−1 and 8.45 ± 0.64, 6.65 ± 0.21, and 5.25 ± 0.49 μg/m2 year−1, respectively. Hg wet deposition flux and precipitation depth were positively correlated at all three sites as were Hg concentration in precipitation and weekly GOM concentrations at the Bronx and Potsdam sites. Scavenging coefficients (SC) of 680, 630, 850 for GOM and 410, 320, and 410 for PBM at Bronx, Rochester, and Potsdam, respectively, suggest GOM is responsible for most of the scavenged Hg. Measured GOM and PBM concentrations were relatively constant before precipitation events and Hg concentrations in precipitation did not vary significantly during precipitation events implying the scavenging process mainly occurred in clouds. VWM Hg concentrations, monthly accumulated Hg flux, and SCs for GOM and PBM were higher at the urban sites and significantly different for non-snow and snow events. Local sources appeared more important at the rural site while regional sources affected high urban concentrations.

Understanding factors influencing the detection of mercury policies in modelled Laurentian Great Lakes wet deposition.

We used chemical transport modelling to better understand the extent to which policy-related anthropogenic mercury emissions changes (a policy signal) can be statistically detected in wet deposition measurements in the Great Lakes region on the subdecadal scale, given sources of noise. In our modelling experiment, we consider hypothetical regional (North American) and global (rest of the world) policy changes, consistent with existing policy efforts (Δglobal = -18%; Δregional = -30%) that divide an eight-year period. The magnitude of statistically significant (p < 0.1) pre- and post-policy period wet deposition differences, holding all else constant except for the policy change, ranges from -0.3 to -2.0% for the regional policy and -0.8 to -2.7% for the global policy. We then introduce sources of noise-trends and variability in factors that are exogenous to the policy action-and evaluate the extent to which the policy signals can still be detected. For instance, technology-related variability in emissions magnitude and speciation can shift the magnitude of differences between periods, in some cases dampening the policy effect. We have found that the interannual variability in meteorology has the largest effect of the sources of noise considered, driving deposition differences between periods to ±20%, exceeding the magnitude of the policy signal. However, our simulations suggest that gaseous elemental mercury concentration may be more robust to this meteorological variability in this region, and a stronger indicator of local/regional emissions changes. These results highlight the potential challenges of detecting statistically significant policy-related changes in Great Lakes wet deposition within the subdecadal scale.

Wet deposition of mercury in Qingdao, a coastal urban city in China: Concentrations, fluxes, and influencing factors

Mercury (Hg) is a global pollutant of public concern because of its high toxicity and capability for worldwide distribution via long-range atmospheric transportation. Wet atmospheric deposition is an important source of Hg in both terrestrial and aquatic environments. Concentrations of various Hg species in precipitation were monitored from March 2016 to February 2017 in a coastal urban area of Qingdao, and their wet deposition fluxes were estimated. The results showed that the volume-weighted mean (VWM) concentrations of total mercury (THg), reactive mercury (RHg), dissolved THg (DTHg), particulate THg (PTHg), total methylmercury (TMeHg), and dissolved and particulate MeHg (DMeHg and PMeHg) in Qingdao's precipitation were 13.6, 1.5, 5.4, 8.2, 0.38, 0.15, and 0.22 ng L−1, respectively, and their annual deposition fluxes were estimated to be 5703.0 (THg), 666.6 (RHg), 2304.0 (DTHg), 3470.4 (PTHg), 161.6 (TMeHg), 64.0 (DMeHg), and 95.7 (PMeHg) ng m−2 y−1, respectively. A relatively high proportion of MeHg in THg was observed in precipitation (3.0 ± 2.6%) possibly due to higher methylation and contributions from an oceanic source to MeHg in the precipitation. Obvious seasonal variations in Hg concentrations and deposition fluxes were observed in the precipitation in Qingdao. Correlation analyses and multiple regression analyses showed that SO2, pH, and NO3− were the controlling factors for THg in precipitation, whereas the MeHg concentration was primarily controlled by the SO2, WS, Cl−, and THg concentrations. PM2.5 and Cl− were the major controlling factors for PMeHg/TMeHg, whereas the TMeHg/THg ratio was mainly influenced by Cl−. The THg and MeHg fluxes were primarily controlled by precipitation, whereas Cl− was also an important factor for the MeHg wet deposition flux. The results of a 72-h backward trajectory analysis in the study region with the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model indicated that Hg deposition in Qingdao mainly originated from four major sources, i.e., the local area, northwestern China, southeastern China and an oceanic source. This oceanic source is an important source of Hg (especially MeHg) in the precipitation in Qingdao.

Atmospheric wet deposition of mercury to the Athabasca Oil Sands Region, Alberta, Canada

Event-based wet deposition of mercury, Hg, was collected in a study from 2010 to 2012 at the AMS 6 site 30 km from the nearest oil sands industrial facilities in Fort McMurray, AB, Canada. For the entire study period (21 months), volume weighted mean, VWM, concentration was 11.2 ng L−1 while total Hg wet deposition was 2.3 μg m−2. Mercury enrichment factors ranged from 10 to 5419 in rainfall, 45–599 in mixed precipitation and 73–266 in snowfall samples. This suggests that emissions from local anthropogenic sources of mercury were available for scavenging especially in rainfall. During a 3-day period in June 2011, there was a 5 to 24-fold increase in mercury enrichment in rainfall samples compared to previous samples. Meteorological analysis during this period provides evidence that mercury containing emissions in smoke from forest fires were transported by winds and subsequently deposited in rainfall received at the sampling site thereby causing enrichment. The magnitude of mercury wet deposition at the AMS 6 site was one of the lowest observed fluxes compared to measurements made elsewhere in the United States and Canada, most likely limited by the low precipitation depths that occurred at this semi-arid location. The reduced wet deposition suggests that mercury dry deposition may be significant in the Athabasca Oil Sands Region, AOSR, and should be addressed in future studies.

Atmospheric mercury in the Southern Hemisphere tropics: seasonal and diurnal variations and influence of inter-hemispheric transport

Abstract. Mercury is a toxic element of serious concern for human and environmental health. Understanding its natural cycling in the environment is an important goal towards assessing its impacts and the effectiveness of mitigation strategies. Due to the unique chemical and physical properties of mercury, the atmosphere is the dominant transport pathway for this heavy metal, with the consequence that regions far removed from sources can be impacted. However, there exists a dearth of long-term monitoring of atmospheric mercury, particularly in the tropics and Southern Hemisphere. This paper presents the first 2 years of gaseous elemental mercury (GEM) measurements taken at the Australian Tropical Atmospheric Research Station (ATARS) in northern Australia, as part of the Global Mercury Observation System (GMOS). Annual mean GEM concentrations determined at ATARS (0.95 ± 0.12 ng m−3) are consistent with recent observations at other sites in the Southern Hemisphere. Comparison with GEM data from other Australian monitoring sites suggests a concentration gradient that decreases with increasing latitude. Seasonal analysis shows that GEM concentrations at ATARS are significantly lower in the distinct wet monsoon season than in the dry season. This result provides insight into alterations of natural mercury cycling processes as a result of changes in atmospheric humidity, oceanic/terrestrial fetch, and convective mixing, and invites future investigation using wet mercury deposition measurements. Due to its location relative to the atmospheric equator, ATARS intermittently samples air originating from the Northern Hemisphere, allowing an opportunity to gain greater understanding of inter-hemispheric transport of mercury and other atmospheric species. Diurnal cycles of GEM at ATARS show distinct nocturnal depletion events that are attributed to dry deposition under stable boundary layer conditions. These cycles provide strong further evidence supportive of a multi-hop model of GEM cycling, characterised by multiple surface depositions and re-emissions, in addition to long-range transport through the atmosphere.