Mercury Wet Scavenging and Deposition Differences by Precipitation Type

Kaulfus, Aaron; Nair, U. S.; Holmes, Christopher D.; Landing, William M.

doi:10.1021/acs.est.6b04187

Cited by 20 publications

(15 citation statements)

References 51 publications

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“…Precipitation amounts and the contribution of UT and MT together explain 55 % of the spatial variation in the observed Hg flux, while individually they explain 25 and 42 % of the spatial variation, respectively. This is consistent with previous studies that have shown higher Hg wet deposition flux in convective thunderstorms that can scavenge Hg(II) present at high altitudes (Guentzel et al, 2001;Shanley et al, 2015;Holmes et al, 2016;Kaulfus et al, 2017).…”

Section: Tagged Tracer Contributions At Mdn and Amnet Sitessupporting

confidence: 93%

“…During the Nitrogen, Oxidants, Mercury, and Aerosol Distributions, Sources, and Sinks (NOMADSS) aircraft campaign, the highest Hg(II) concentrations (300-680 pg m −3 ) were observed in clean and dry air (CO < 75 ppbv and relative humidity (RH) < 35 %) originating in the subsiding air masses of the Pacific and the Atlantic subtropical anticyclones Shah et al, 2016). Furthermore, higher concentrations of Hg in precipitation are observed in thunderstorms reaching higher altitudes (Guentzel et al, 2001;Shanley et al, 2015;Holmes et al, 2016;Kaulfus et al, 2017), and higher Hg wet and dry deposition fluxes are associated with transport from the free troposphere Gustin et al, 2012;Huang and Gustin, 2012;Sheu and Lin, 2013).…”

Section: Introductionmentioning

confidence: 99%

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Subtropical subsidence and surface deposition of oxidized mercury produced in the free troposphere

Shah

Jaeglé

2017

Atmos. Chem. Phys.

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Abstract. Oxidized mercury (Hg(II)) is chemically produced in the atmosphere by oxidation of elemental mercury and is directly emitted by anthropogenic activities. We use the GEOS-Chem global chemical transport model with gaseous oxidation driven by Br atoms to quantify how surface deposition of Hg(II) is influenced by Hg(II) production at different atmospheric heights. We tag Hg(II) chemically produced in the lower (surface-750 hPa), middle (750-400 hPa), and upper troposphere (400 hPa-tropopause), in the stratosphere, as well as directly emitted Hg(II). We evaluate our 2-year simulation (2013)(2014) against observations of Hg(II) wet deposition as well as surface and free-tropospheric observations of Hg(II), finding reasonable agreement. We find that Hg(II) produced in the upper and middle troposphere constitutes 91 % of the tropospheric mass of Hg(II) and 91 % of the annual Hg(II) wet deposition flux. This large global influence from the upper and middle troposphere is the result of strong chemical production coupled with a long lifetime of Hg(II) in these regions. Annually, 77-84 % of surface-level Hg(II) over the western US, South America, South Africa, and Australia is produced in the upper and middle troposphere, whereas 26-66 % of surface Hg(II) over the eastern US, Europe, and East Asia, and South Asia is directly emitted. The influence of directly emitted Hg(II) near emission sources is likely higher but cannot be quantified by our coarse-resolution global model (2 • latitude × 2.5 • longitude). Over the oceans, 72 % of surface Hg(II) is produced in the lower troposphere because of higher Br concentrations in the marine boundary layer. The global contribution of the upper and middle troposphere to the Hg(II) dry deposition flux is 52 %. It is lower compared to the contribution to wet deposition because dry deposition of Hg(II) produced aloft requires its entrainment into the boundary layer, while rain can scavenge Hg(II) from higher altitudes more readily. We find that 55 % of the spatial variation of Hg wet deposition flux observed at the Mercury Deposition Network sites is explained by the combined variation of precipitation and Hg(II) produced in the upper and middle troposphere. Our simulation points to a large role of the dry subtropical subsidence regions. Hg(II) present in these regions accounts for 74 % of Hg(II) at 500 hPa over the continental US and more than 60 % of the surface Hg(II) over high-altitude areas of the western US. Globally, it accounts for 78 % of the tropospheric Hg(II) mass and 61 % of the total Hg(II) deposition. During the Nitrogen, Oxidants, Mercury, and Aerosol Distributions, Sources, and Sinks (NOMADSS) aircraft campaign, the contribution of Hg(II) from the dry subtropical regions was found to be 75 % when measured Hg(II) exceeded 250 pg m −3 . Hg(II) produced in the upper and middle troposphere subsides in the anticyclones, where the dry conditions inhibit the loss of Hg(II). Our results highlight the importance the subtropical anticyclones as the primary conduits for t...

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Section: Tagged Tracer Contributions At Mdn and Amnet Sitessupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Subtropical subsidence and surface deposition of oxidized mercury produced in the free troposphere

Shah

Jaeglé

2017

Atmos. Chem. Phys.

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“…Other research attributed substantial contributions from local and regional Hg emissions sources to precipitation-Hg deposition in the Midwestern USA [19,20,54,55]. According to Holmes et al [56] and Kaulfus et al [57], warm weather, convective thunderstorms are believed to increase Hg deposition and this may be the case for many of the extreme episodes examined in this study. Such storms can incorporate additional GOM formed in the troposphere from GEM originating at local and regional sources [55], in addition to effective below-cloud and in-cloud scavenging of GOM, as described by Lynam et al [58].…”

Section: Percentage Ofmentioning

confidence: 49%

Spatial Patterns and Temporal Changes in Atmospheric-Mercury Deposition for the Midwestern USA, 2001–2016

Risch

Kenski²

2018

Atmosphere

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Spatial patterns and temporal changes in atmospheric-mercury (Hg) deposition were examined in a five-state study area in the Midwestern USA where 32% of the stationary sources of anthropogenic Hg emissions in the continental USA were located. An extensive monitoring record for wet and dry Hg deposition was compiled for 2001-2016, including 4666 weekly precipitation samples at 13 sites and 27 annual litterfall-Hg samples at 7 sites. This study is the first to examine these Hg data for the Midwestern USA. The median annual precipitation-Hg deposition at the study sites was 10.4 micrograms per square meter per year (µg/m 2 /year) and ranged from 5.8 µg/m 2 /year to 15.0 µg/m 2 /year. The median annual Hg concentration was 9.4 ng/L. Annual litterfall-Hg deposition had a median of 16.1 µg/m 2 /year and ranged from 9.7 to 23.4 µg/m 2 /year. Isopleth maps of annual precipitation-Hg deposition indicated a recurring spatial pattern similar to one revealed by statistical analysis of weekly precipitation-Hg deposition. In that pattern, high Hg deposition in southeastern Indiana was present each year, frequently extending to southern Illinois. Most of central Indiana and central Illinois had similar Hg deposition. Areas with comparatively lower annual Hg deposition were observed in Michigan and Ohio for many years and frequently included part of northern Indiana. The area in southern Indiana where high Hg deposition predominated had the highest number of extreme episodes of weekly Hg deposition delivering up to 15% of the annual Hg load from precipitation in a single week. Modeled 48-h back trajectories indicated air masses for these episodes often arrived from the south and southwest, crossing numerous stationary sources of Hg emissions releasing from 23 to more than 300 kg Hg per year. This analysis suggests that local and regional, rather than exclusively continental or global Hg emissions were likely contributing to the extreme episodes and at least in part, to the spatial patterns of precipitation-Hg deposition in the study area. Statistically significant temporal decreases in weekly precipitation-Hg concentrations in the study area between the periods 2001-2013 and 2014-2016 were observed, coinciding with reported reductions in Hg emissions in the USA required by implementation of national Hg emissions-control rules. These decreases in atmospheric-Hg concentrations are believed to have resulted in the reduced atmospheric-Hg deposition recorded because precipitation depths between the two periods were not significantly different. The Hg-monitoring data for the study area identified an atmospheric deposition response to decreased local and regional Hg emissions.

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“…Event-based wet precipitations (rain and snow) were collected for mercury (Hg) and trace element analyses. Though weekly collections are much more common, event-based precipitation samples provide the best opportunity to study how mercury is scavenging from the atmosphere [49]. The type of precipitation and meteorological conditions (start and end time of precipitation collection, air temperature during precipitation, wind direction, humidity, etc.)…”

Section: Sample Collection and Analytical Proceduresmentioning

confidence: 99%

Assessment of Mercury Concentrations and Fluxes Deposited from the Atmosphere on the Territory of the Yamal-Nenets Autonomous Area

2021

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The problem of mercury input and its further distribution in the Arctic environment is actively debated, especially in recent times, due to the observed processes of permafrost thawing causing the enhanced release of mercury into the Arctic atmosphere and further distribution in the terrestrial and aquatic ecosystem. The atmospheric mercury deposition occurs via dry deposition and wet scavenging by precipitation events. Here we present a study of Hg in wet precipitation on the remote territory of the Russian Arctic; the data were obtained at the monitoring stations Nadym and Salekhard in 2016–2018. Mercury pollution of the Salekhard atmosphere in cold time is mainly determined by regional and local sources, while in Nadym, long-range transport of mercury and local fuel combustion are the main sources of pollutants in the cold season, while internal regional sources have a greater impact on the warm season. Total mercury concentrations in wet precipitation in Nadym varied from <0.5 to 63.3 ng/L. The highest Hg concentrations in the springtime were most likely attributed to atmospheric mercury depletion events (AMDE). The contributions of wet atmospheric precipitation during the AMDE period to the annual Hg deposition were 16.7% and 9.8% in 2016/2017 and 2017/2018, respectively. The average annual volume-weighted Hg concentration (VWC) in the atmospheric precipitation in Nadym is notably higher than the values reported for the remote regions in the Arctic and comparable with the values obtained for the other urbanized regions of the world. Annual Hg fluxes in Nadym are nevertheless close to the average annual fluxes for remote territories of the Arctic zone and significantly lower than the annual fluxes reported for unpolluted sites of continental-scale monitoring networks of the different parts of the world (USA, Europe, and China). The increase of Hg deposition flux with wet precipitation in Nadym in 2018 might be caused by regional emissions of gas and oil combustion, wildfires, and Hg re-emission from soils due to the rising air temperature. The 37 cm increase of the seasonally thawed layer (STL) in 2018 compared to the 10-year average reflects that the climatic changes in the Nadym region might increase Hg(0) evasion, considering a great pool of Hg is contained in permafrost.

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Mercury Wet Scavenging and Deposition Differences by Precipitation Type

Cited by 20 publications

References 51 publications

Subtropical subsidence and surface deposition of oxidized mercury produced in the free troposphere

Subtropical subsidence and surface deposition of oxidized mercury produced in the free troposphere

Spatial Patterns and Temporal Changes in Atmospheric-Mercury Deposition for the Midwestern USA, 2001–2016

Assessment of Mercury Concentrations and Fluxes Deposited from the Atmosphere on the Territory of the Yamal-Nenets Autonomous Area

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