Gaseous Oxidized Mercury Concentrations Research Articles

Pollution status and source resolution of atmospheric mercury in the intersectional region of Northern Philippines, southern Taiwan, and northern South China Sea

A four-season sampling of speciated atmospheric mercury (SAM) was employed in East Asia. Three mercury species including gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particulate mercury (PHg) were measured at three background sites. This study explored the temporal variation, spatial distribution, gas-solid partition, transport routes, and source resolution of SAM. The yearly average concentrations of GEM, GOM, and PHg were 2.76 ± 0.36 ng/m3, 23.14 ± 8.67 pg/m3, and 0.23 ± 0.058 ng/m3. The highest GEM and PHg concentrations occurred at Laoag (northern Philippines) in spring, while that of GOM was observed at Laoag but in summer. The lowest GEM and PHg concentrations always occurred at Dongsha Islands (northern South China Sea) in summer, while that of GOM was also observed at Dongsha Islands but in fall. SAM was partition as showed 92.64–96.72% of total gas-phase mercury (TGM) and 3.28–7.36% of solid phase mercury. Eight clustered transport routes were resolved by a HYSPLIT model with polluted air parcels originating from Central/North China. Routes from Indochina Peninsula and South China showed the highest GEM concentration. Moreover, air parcels transported from West Pacific Ocean and South China Sea (SCS) had the lowest concentration of GEM. High concentrations of SAM in the region were mainly attributed to long-range transport (LRT) from Asian continental outflows (ACOs). We further revealed that GEM was positively correlated to SO2, CO, NOx, and PM2.5, but negatively correlated to O3. GOM was positively correlated to SO2, O3, NOx, and PM2.5, but negatively correlated to CO, While, PHg was positively correlated to SO2, CO, O3, NOx, and PM2.5.

Long-range transport of atmospheric speciated mercury from the eastern waters of Taiwan Island to northern South China Sea

This study explored the temporospatial distribution, gas-particle partition, and pollution sources of atmospheric speciated mercury (ASM) from the eastern offshore waters of the Taiwan Island (TI) to the northern South China Sea (SCS). Both gaseous and particulate mercury were simultaneously sampled at three remote sites in four seasons. The average concentrations of gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particulate bound mercury (PBM) were 2.05 ± 0.45 ng/m3, 19.17 ± 5.39 pg/m3, and 0.11 ± 0.06 ng/m3, respectively. The concentrations of GEM and PBM in the cold seasons were higher than those in the warm seasons, but those of GOM had an opposite trend. In terms of gas-solid partition, ASM was apportioned as 91.3–97.3% of GEM and 2.7–8.7% of GOM and PBM. The average concentrations of GEM, GOM, and PBM at the Green Island (GI) were 2.21 ± 0.47 ng/m3, 22.31 ± 5.35 pg/m3, and 0.12 ± 0.06 ng/m3; those at the Kenting Peninsula (KT) were 2.11 ± 0.43 ng/m3, 20.57 ± 4.38 pg/m3, and 0.11 ± 0.06 ng/m3; and those at the Dongsha Islands (DS) were 1.84 ± 0.40 ng/m3, 15.19 ± 3.58 pg/m3, and 0.08 ± 0.05 ng/m3, respectively. Overall, the spatial distribution of ASM concentrations showed the order as: GI > KT > DS. Air masses blown mainly from the West Pacific Ocean (WPO) and SCS in summer showed the lowest ASM concentrations. Oppositely, high ASM concentrations were commonly observed in spring and winter when polluted air masses were blown by Asian Northeastern Monsoons (ANMs). The transport routes of polluted air masses were originated mainly from North China, Central China, Northeast China, Korea and Japan, and mostly passed through the urban and industrial regions in the northeastern Asian countries.

Seasonal variation and source identification of atmospheric speciated mercury in an industrial harbor area in East Asia

In this study, the pollution characteristics, spatiotemporal variation, and potential sources of atmospheric speciated mercury (ASM) in an industrial harbor area were explored. Gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particle-bound mercury (PBM) were sampled by a self-designed manual system at three harbor sites in four seasons. The yearly average concentrations of GEM, GOM, and PBM were 6.7 ± 2.0 ng/m3, 244 ± 70 pg/m3, and 410 ± 105 pg/m3, respectively. The seasonal average ASM concentration was in the order of: winter > fall > spring > summer. In terms of species, GEM dominated ASM, while reactive mercury (RM = GOM + PBM) accounted for 6.0–15.7%of ASM, implying that ASM was governed by anthropogenic sources in the harbor area. The highest ASM concentrations were observed at Site Zhonghe (ZH), which is mainly influenced by both ship exhausts and industrial emissions, and positively correlated with CO, NOx, and SO2. In particular, GOM was positively correlated with O3, and negatively correlated with air temperature and relative humidity, showing high impact from atmospheric photochemical reactions. Air masses transporting westerly in spring were mainly from ship exhausts. In summer, air masses transporting from the south were from utility power plants and machinery exhausts. In fall and winter, air masses were transported mainly from the north, blowing by the long-range transport of polluted air masses originated from the north. Both principal component analysis and positive matrix factorization results indicate that coal burning, industrial emissions, and vehicular exhausts are the main contributors to ASM. Site Zhongdao (ZD) was close to the bulk carrier loading and unloading zones and was highly influenced by mobile sources, while Site ZH was mainly influenced by the neighboring industrial complex.

Dynamics of gaseous oxidized mercury at Villum Research Station during the High Arctic summer

Abstract. While much research has been devoted to the subject of gaseous elemental mercury (GEM) and gaseous oxidized mercury (GOM) in the Arctic spring during atmospheric mercury depletion events, few studies have examined the behavior of GOM in the High Arctic summer. GOM, once deposited and incorporated into the ecosystem, can pose a threat to human and wildlife health, though there remain large uncertainties regarding the transformation, deposition, and assimilation of mercury into the food web. Therefore, to further our understanding of the dynamics of GOM in the High Arctic during the late summer, we performed measurements of GEM and GOM, along with meteorological parameters and atmospheric constituents, and utilized modeled air mass history during two summer campaigns in 2019 and 2020 at Villum Research Station (Villum) in northeastern Greenland. Seven events of enhanced GOM concentrations were identified and investigated in greater detail. In general, the common factors associated with event periods at ground level were higher levels of radiation and lower H2O mixing ratios, accumulated precipitation, and relative humidity (RH), although none were connected with cold temperatures. Non-event periods at ground level each displayed a different pattern in one or more parameters when compared to event periods. Generally, air masses during event periods for both campaigns were colder and drier, arrived from higher altitudes, and spent more time above the mixed layer and less time in a cloud compared to non-events, although some events deviated from this general pattern. Non-event air masses displayed a different pattern in one or more parameters when compared to event periods, although they were generally warmer and wetter and arrived from lower altitudes with little radiation. Coarse-mode aerosols were hypothesized to provide the heterogenous surface for halogen propagation during some of the events, while for others the source is unknown. While these general patterns were observed for event and non-event periods, analysis of individual events showed more specific origins. Five of the seven events were associated with air masses that experienced similar conditions: transported from the cold, dry, and sunlit free troposphere. However, two events experienced contrasting conditions, with air masses being warm and wet with surface layer contact under little radiation. Two episodes of extremely high levels of NCoarse and BC, which appear to originate from flaring emissions in Russia, did not contribute to enhanced GOM levels. This work aims to provide a better understanding of the dynamics of GOM during the High Arctic summer.

Development of an Understanding of Reactive Mercury in Ambient Air: A Review

This review focuses on providing the history of measurement efforts to quantify and characterize the compounds of reactive mercury (RM), and the current status of measurement methods and knowledge. RM collectively represents gaseous oxidized mercury (GOM) and that bound to particles. The presence of RM was first recognized through measurement of coal-fired power plant emissions. Once discovered, researchers focused on developing methods for measuring RM in ambient air. First, tubular KCl-coated denuders were used for stack gas measurements, followed by mist chambers and annular denuders for ambient air measurements. For ~15 years, thermal desorption of an annular KCl denuder in the Tekran® speciation system was thought to be the gold standard for ambient GOM measurements. Research over the past ~10 years has shown that the KCl denuder does not collect GOM compounds with equal efficiency, and there are interferences with collection. Using a membrane-based system and an automated system—the Detector for Oxidized mercury System (DOHGS)—concentrations measured with the KCl denuder in the Tekran speciation system underestimate GOM concentrations by 1.3 to 13 times. Using nylon membranes it has been demonstrated that GOM/RM chemistry varies across space and time, and that this depends on the oxidant chemistry of the air. Future work should focus on development of better surfaces for collecting GOM/RM compounds, analytical methods to characterize GOM/RM chemistry, and high-resolution, calibrated measurement systems.

Isotopic composition of total gaseous mercury at a high-altitude tropical forest site influenced by air masses from the East Asia continent and the Pacific Ocean

Gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), particulate-bound mercury (PBM), and the isotopic composition of total gaseous mercury (TGM = GEM + GOM) were measured at the Lulin Atmospheric Background Station (LABS), a mountain background site downwind of the East Asia continent, from February 2015 to January 2016. Mean (±S.D.) concentrations of GEM, GOM, and PBM were 1.54 ± 0.34 ng m−3, 14.0 ± 27.8 pg m−3, and 2.6 ± 3.7 pg m−3, respectively. Concentration-Weighted Trajectory (CWT) analysis indicated that East and coastal China were the main source regions of elevated GEM observed at LABS. Weekly integrated TGM showed significant variations in δ202HgTGM (−0.42 to 0.41‰) and Δ199HgTGM (−0.31 to −0.13‰). Both δ202HgTGM and Δ199HgTGM showed clear seasonal variations, but the seasonal pattern of δ202HgTGM was different from that of Δ199HgTGM. The lowest mean δ202HgTGM was observed in spring (−0.15‰), while the lowest mean Δ199HgTGM was observed in summer (−0.24‰). A significant positive correlation (R2 = 0.38, p < 0.01) existed between δ202HgTGM and normalized difference vegetation index (NDVI), suggesting vegetation activity was an important factor controlling the seasonal variation of δ202HgTGM. In contrast, air mass transport path, which influences the source region of TGM to LABS, was likely the driver for the seasonal variations of Δ199HgTGM. Furthermore, results from the air mass classification showed distinguishable Δ199HgTGM signature for different air mass source regions, with air masses from South China Sea and western Pacific Ocean being characterized by more negative Δ199HgTGM (−0.25 ± 0.04‰). Results of this research demonstrated a clear difference in isotopic compositions of atmospheric Hg between continental and marine air masses.

Spatiotemporal distribution and long-range transport of atmospheric speciated mercury at three remote islands in Taiwan Strait and South China Sea

This study investigated the spatiotemporal distribution and long-range transport of atmospheric speciated mercury at three remote islands in the Taiwan Strait and the South China Sea. The field measured speciated mercury in the atmosphere was then correlated with criteria air pollutants and meteorological parameters. Air mass trajectory simulation and global fire map were further used to explore potential source regions. Field measurement results showed that the yearly average concentration of gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particulate mercury (PHg) in the target seas were 2.09±0.61 ng/m3, 20.93±7.81 pg/m3, and 150±70 pg/m3, respectively. The highest GEM, GOM, and PHg concentrations were always observed at the Penghu Islands in all seasons. Total gaseous mercury (TGM = GEM+GOM) was the dominant mercury species in the atmosphere, apportioned as 92.46– 96.17% TGM and 3.83– 8.70% PHg, respectively. The seasonal variation of GEM and PHg concentrations were ordered as: spring>winter>fall>summer, while GOM showed different seasonal trends. The lowest concentration of total atmospheric mercury (TAM) was observed in summer since clean air masses were blown mainly from the Pacific Ocean and the Philippines Islands. Air masses came mainly from Central China, North China, and Japan/Korea with the TAM concentrations of 2.90 ± 0.63, 2.68 ± 0.65, and 2.16 ± 0.45 ng/m3, and the frequencies of 19.3%, 18.3%, and 14.3%, respectively. Atmospheric speciated mercury positively correlated to O3, PM2.5, SO2, and NOx, implying that they were consistently emitted from anthropogenic sources in the upwind polluted regions. Overall, the concentrations of atmospheric speciated mercury measured at the three remote islands in the Taiwan Strait and the South China Sea were commonly higher than those in the United States and European countries, but lower than those in Asian countries, with the exception of Japan.

Comparison of 4 Methods for Measurement of Reactive, Gaseous Oxidized, and Particulate Bound Mercury.

The atmosphere is an important (1) pathway by which mercury (Hg) is transported around the globe and (2) source of Hg to ecosystems. Thus, understanding Hg atmospheric chemistry is critical for understanding the biogeochemical cycle and impacts to human and ecosystem health. Work over the past 13 years has demonstrated that the standard instrument used to measure atmospheric Hg does not accurately quantify gaseous oxidized mercury (GOM) or particulate bound mercury (PBM). This study focused on comparing four methods for quantifying atmospheric Hg and identifying Hg(II) compounds. Data from two automated systems, the Tekran 2537/1130 system and the University of Nevada, Reno-Dual Channel System (DCS), were compared with two University of Nevada, Reno-Reactive Mercury Active Systems (RMAS 2.0). One RMAS 2.0 included cation exchange membranes (CEMs) and nylon membranes, and the second included a polytetrafluoroethylene (PTFE) membrane upstream of the CEM and nylon membranes. The Tekran system and the DCS underestimated GOM concentrations with respect to that measured using the RMAS 2.0. The RMAS 2.0 with the upstream PTFE provided a means of distinguishing GOM and PBM. Thermal desorption of nylon membrane data identified a variety of GOM and PBM compounds present.

Characteristics of atmospheric mercury at a suburban site in northern Taiwan and influence of trans-boundary haze events

Concentrations of gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particle-bound mercury (PBM) were measured at a suburban site in northern Taiwan between October 2017 and September 2018. Mean concentrations of GEM, GOM, and PBM were 2.61 ± 6.47 ng m−3, 12.1 ± 34.3 pg m−3, and 18.7 ± 86.8 pg m−3, respectively. On 35% of the days, elevated atmospheric mercury (Hg) concentration occurred between midnight and early morning when local wind direction shifted and came from sectors between SSW and S, indicating influence of local anthropogenic emission sources. As such, a diurnal pattern with nighttime peaks was observed for GEM, GOM, and PBM. However, elevated GOM values were also observed around noon on 87 occasions, coinciding with peak O3 and solar radiation, suggesting additional contribution from in situ photochemical reactions. Seasonally, atmospheric Hg concentrations were higher in spring than in the other seasons. Besides the contribution from local emissions and the East Asian outflow, lower wind speed, cumulative rainfall, and days of rain in spring suggesting poor air dispersion and inefficient pollutant removal, hence leading to the accumulation of atmospheric Hg and thus higher concentrations. Two trans-boundary haze events from China were encountered during this study. Concentrations of GEM and PBM were enhanced on haze days, with particularly significant enhancement in PBM. Comparison of the maximum PBM values during these haze events to respective pre-event PBM values showed enhancements of 378% and 1438%, whereas enhancements of 100% and 147% were observed for GEM. GOM remained relatively low and stable during haze events, which could be due to the favored partitioning of GOM toward solid phase under high PM2.5 concentrations and the lack of sunlight to fuel the photochemical production of GOM. Backward trajectories indicated that Hg emissions in east China likely contributed to the enhancements in atmospheric Hg concentrations measured at the suburban site in northern Taiwan during these two trans-boundary haze events.

Long-Term Observation of Atmospheric Speciated Mercury during 2007–2018 at Cape Hedo, Okinawa, Japan

The concentrations of atmospheric gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particle-bound mercury (particles with diameter smaller than 2.5 μm; PBM2.5) were continuously observed for a period of over 10 years at Cape Hedo, located on the north edge of Okinawa Island on the border of the East China Sea and the Pacific Ocean. Regional or global scale mercury (Hg) pollution affects their concentrations because no local stationary emission sources of Hg exist near the observation site. Their concentrations were lower than those at urban and suburban cities, as well as remote sites in East Asia, but were slightly higher than the background concentrations in the Northern Hemisphere. The GEM concentrations exhibited no diurnal variations and only weak seasonal variations, whereby concentrations were lower in the summer (June–August). An annual decreasing trend for GEM concentrations was observed between 2008 and 2018 at a rate of −0.0382 ± 0.0065 ng m−3 year−1 (−2.1% ± 0.36% year−1) that was the same as those in Europe and North America. Seasonal trend analysis based on daily median data at Cape Hedo showed significantly decreasing trends for all months. However, weaker decreasing trends were observed during the cold season from January to May, when air masses are easily transported from the Asian continent by westerlies and northwestern monsoons. Some GEM, GOM, and PBM2.5 pollution events were observed more frequently during the cold season. Back trajectory analysis showed that almost all these events occurred due to the substances transported from the Asian continent. These facts suggested that the decreasing trend observed at Cape Hedo was influenced by the global decreasing GEM trend, but the rates during the cold season were restrained by regional Asian outflows. On the other hand, GOM concentrations were moderately controlled by photochemical production in summer. Moreover, both GOM and PBM2.5 concentrations largely varied during the cold season due to the influence of regional transport rather than the trend of atmospheric Hg on a global scale.

Factors influencing concentrations of atmospheric speciated mercury measured at the farthest island West of South Korea

East Asia is the largest emitter of mercury (Hg) in the world, but only a few studies of speciated Hg have been carried out in South Korea. In this study, total gaseous mercury (TGM), gaseous oxidized mercury (GOM), and particulate bound mercury (PBM) were measured at one of the most northwestern islands of South Korea. Concentrations of TGM and GOM were similar to those measured in other regions of Korea; however, PBM was found in much higher concentrations during cold months, most likely from coal and biomass burning in North Korea. Sources outside Korea significantly affected TGM and PBM, and GOM increased as air masses transported from domestic coal-burning power plants. During the warm months, GOM increased as gaseous elemental mercury (GEM) decreased when air masses were confined within the ocean area with minimal influence from anthropogenic emissions. This implies that there is an efficient process for the oxidation of GEM and GOM production in the marine boundary layer. The concentrations of ozone also decreased as an increase in GOM was observed, suggesting that halogens are primarily responsible for GEM oxidation.

First measurement of atmospheric mercury species in Qomolangma Natural Nature Preserve, Tibetan Plateau, and evidence oftransboundary pollutant invasion

Abstract. Located in the world's “third pole” and a remote region connecting the Indian plate and the Eurasian plate, Qomolangma National Nature Preserve (QNNP) is an ideal region to study the long-range transport of atmospheric pollutants. In this study, gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM) and particle-bound mercury (PBM) were continuously measured during the Indian monsoon transition period in QNNP. A slight increase in the GEM concentration was observed from the period preceding the Indian summer monsoon (1.31±0.42 ng m−3) to the Indian summer monsoon period (1.44±0.36 ng m−3), while significant decreases were observed in the GOM and PBM concentrations, with concentrations decreasing from 35.2±18.6 to 19.3±10.9 pg m−3 (p &lt; 0.001) for GOM and from 30.5±12.5 to 24.9±19.8 pg m−3 (p &lt; 0.001) for PBM. A unique daily pattern was observed in QNNP with respect to the GEM concentration, with a peak value before sunrise and a low value at noon. Relative to the (low) GEM concentrations, GOM concentrations (with a mean value of 21.4±13.4 pg m−3, n=1239) in this region were relatively high compared with the measured values in some other regions of China. A cluster analysis indicated that the air masses transported to QNNP changed significantly at different stages of the monsoon, and the major potential mercury (Hg) sources shifted from northern India and western Nepal to eastern Nepal and Bangladesh. As there is a large area covered in glaciers in QNNP, local glacier winds could increase the transboundary transport of pollutants and transport polluted air masses to the Tibetan Plateau. The atmospheric Hg concentration in QNNP in the Indian summer monsoon period was influenced by transboundary Hg flows. This highlights the need for a more specific identification of Hg sources impacting QNNP and underscores the importance of international cooperation regarding global Hg controls.

Isotopic Composition of Gaseous Elemental Mercury in the Marine Boundary Layer of East China Sea

AbstractCharacterizing the speciation and isotope signatures of atmospheric mercury (Hg) downwind of mainland China is critical to understanding the outflow of Hg emission and the contributing sources. In this study, we measured the concentrations of gaseous elemental mercury (GEM), particulate bound mercury, gaseous oxidized mercury, and the GEM isotopic composition in the marine boundary layer of East China Sea from October 2013 to January 2014. Mean (±1σ) GEM, particulate bound mercury, and gaseous oxidized mercury concentrations were 2.25 ± 1.03 ng/m3, 26 ± 38 pg/m3, and 8 ± 10 pg/m3, respectively. Most events of elevated GEM are associated with the outflow of Hg emissions in mainland China. The 24‐ and 48‐hr integrated GEM samples showed large variations in both δ202Hg (−1.63‰ to 0.34‰) and Δ199Hg (−0.26‰ to −0.02‰). GEM δ202Hg and Δ199Hg were negatively and positively correlated to its atmospheric concentrations, respectively, suggesting a binary physical mixing of regional background GEM and Hg emissions in mainland China. Using a binary mixing model, highly negative δ202Hg (−1.79 ± 0.24‰, 1σ) and near‐zero Δ199Hg (0.02 ± 0.04‰, 1σ) signatures for China GEM emissions are predicted. Such isotopic signatures are significantly different from those found in North America and Europe and the background global/regional atmospheric GEM pool. It is likely that emissions from industrial and residential coal combustion (lacking conventional air pollutant control devices), cement and mercury production, biomass burning, and soil emissions contributed significantly to the estimated isotope signatures of GEM emissions in China.

Atmospheric Mercury Temporal Trends in the Northeastern United States from 1992 to 2014: Are Measured Concentrations Responding to Decreasing Regional Emissions?

Long-term atmospheric mercury measurements at Underhill, VT (VT99), and Huntington Forest, NY (NY20), from 1992 to 2014 and 2005 to 2014, respectively, were used to determine concentration trends using Mann–Kendall’s tau test with Sen’s slope estimator. These data, measured generally downwind of large Hg sources in the Midwestern United States, provide the longest record of ambient Hg concentrations available in the United States. At VT99, concentrations of gaseous element mercury (GEM), gaseous oxidized mercury (GOM), and particle-bound mercury (PBM) declined at rates of −1.8, −3.2, and −6.7%/year, respectively. At NY20, GEM and GOM concentrations declined at rates of −1.6 and −7.8%/year, respectively; however, PBM concentrations increased at a rate of 2.0%/year, which is likely related to winter wood burning. A trajectory ensemble analysis using the potential source contribution function indicates the source locations associated with high mercury concentrations changed from Toronto–Buffalo and Pennsylva...

Atmospheric mercury speciation in Shanghai, China

GEM (Gaseous elemental mercury), fine fraction (<2.5μm) PBM (Particle-bound mercury) and GOM (Gaseous oxidized mercury) were continuously monitored from Jun 1 to Dec 31 2014 at a suburban site in Shanghai. The average concentrations of GEM, PBM and GOM were 4.19±9.13ng·m−3, 197±877pg·m−3, 21±100pg·m−3, respectively, which were all much higher than those at urban sites in Europe and North America and rural areas of China, but lower than those at urban sites of China. The concentrations of the three mercury species were all found with the highest concentration in December than those in summer. Overall, GEM varied little and PBM exhibited higher level during the night, while GOM typically peaked in the noon and afternoon which is consistent with that of ozone, indicating that GOM may depend on the stronger photochemical reactions during the daytime. Despite of the weak correlations of GEM with SO2 (r=0.14, p<0.0001) and NOX (r=0.17, p<0.0001), GEM, PBM, SO2 and NOx exhibited similar diurnal trend, suggesting that coal combustion might be the important sources of mercury in Shanghai because there is no mercury mining companies and few mercuric manufacturers in Shanghai. The strong correlation of PBM with GEM and GOM showed that directly anthropogenic emission was an important source of GEM and PBM, but the gas-particle partitioning of GOM and GEM might be also another source of PBM. The lower GEM/CO ratio of 3.9 (ng·m−3·ppmv−1) in Shanghai than that for mainland China and non-ferrous smelting factories were related to the few non-ferrous smelting factories around Shanghai. The results from the potential source contribution function (PSCF) model furtherly illustrated that in Shanghai the concentration of GEM in summer and autumn might be highly impacted by the local and regional source but wasn't heavily affected by long-range transport.

Speciated atmospheric mercury on haze and non-haze days in an inland city in China

Abstract. Long-term continuous measurements of speciated atmospheric mercury were conducted from July 2013 to June 2014 in Hefei, a midlatitude inland city in eastern central China that experiences frequent haze pollution. The mean concentrations (±standard deviation) of gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM) and particle-bound mercury (PBM) were 3.95 ± 1.93 ng m−3, 2.49 ± 2.41 and 23.3 ± 90.8 pg m−3, respectively, on non-haze days, and 4.74 ± 1.62 ng m−3, 4.32 ± 8.36 and 60.2 ± 131.4 pg m−3, respectively, on haze days. Potential source contribution function (PSCF) analysis suggested that atmospheric mercury pollution on haze days was caused primarily by local emissions, instead of via long-range transport. The poorer mixing conditions on haze days also favored the accumulation of atmospheric mercury. Compared to GEM and GOM, PBM was especially sensitive to haze pollution. The mean PBM concentration on haze days was 2.5 times that on non-haze days due to elevated concentrations of particulate matter. PBM also showed a clear seasonal trend; its concentration was the highest in fall and winter, decreased rapidly in spring and was the lowest in summer, following the same order in the frequency of haze days in different seasons. On both non-haze and haze days, GOM concentrations remained low at night, but increased rapidly just before sunrise, which could be due to diurnal variation in air exchange between the boundary layer and free troposphere. However, non-haze and haze days showed different trends in daytime GEM and GOM concentrations. On non-haze days, GEM and GOM declined synchronously through the afternoon, probably due to the retreat of the free tropospheric air as the height of the atmospheric boundary layer increases. In contrast, on haze days, GOM and GEM showed opposite trends with the highest GOM and lowest GEM observed in the afternoon, suggesting the occurrence of photochemical oxidation. This is supported by simple box-model calculations, which showed that oxidation of GEM to GOM does occur and that the transport of free tropospheric GOM alone is not large enough to account for the observed increase in daytime GOM. Our results further postulate that NO2 aggregation with the HgOH intermediate may be a potential mechanism for the enhanced production of GOM during daytime.

Atmospheric mercury speciation dynamics at the high-altitude Pic du Midi Observatory, southern France

Abstract. Continuous measurements of atmospheric gaseous elemental mercury (GEM), particulate bound mercury (PBM) and gaseous oxidized mercury (GOM) at the high-altitude Pic du Midi Observatory (PDM Observatory, 2877 m a.s.l.) in southern France were made from November 2011 to November 2012. The mean GEM, PBM and GOM concentrations were 1.86 ng m−3, 14 pg m−3 and 27 pg m−3, respectively and we observed 44 high PBM (peak PBM values of 33–98 pg m−3) and 61 high GOM (peak GOM values of 91–295 pg m−3) events. The high PBM events occurred mainly in cold seasons (winter and spring) whereas high GOM events were mainly observed in the warm seasons (summer and autumn). In cold seasons the maximum air mass residence times (ARTs) associated with high PBM events were observed in the upper troposphere over North America. The ratios of high PBM ARTs to total ARTs over North America, Europe, the Arctic region and Atlantic Ocean were all elevated in the cold season compared to the warm season, indicating that the middle and upper free troposphere of the Northern Hemisphere may be more enriched in PBM in cold seasons. PBM concentrations and PBM ∕ GOM ratios during the high PBM events were significantly anti-correlated with atmospheric aerosol concentrations, air temperature and solar radiation, suggesting in situ formation of PBM in the middle and upper troposphere. We identified two distinct types of high GOM events with the GOM concentrations positively and negatively correlated with atmospheric ozone concentrations, respectively. High GOM events positively correlated with ozone were mainly related to air masses from the upper troposphere over the Arctic region and middle troposphere over the temperate North Atlantic Ocean, whereas high GOM events anti-correlated with ozone were mainly related to air masses from the lower free troposphere over the subtropical North Atlantic Ocean. The ARTs analysis demonstrates that the lower and middle free troposphere over the North Atlantic Ocean was the largest source region of atmospheric GOM at the PDM Observatory. The ratios of high GOM ARTs to total ARTs over the subtropical North Atlantic Ocean in summer were significantly higher than those over the temperate and sub-arctic North Atlantic Ocean as well as that over the North Atlantic Ocean in other seasons, indicating abundant in situ oxidation of GEM to GOM in the lower free troposphere over the subtropical North Atlantic Ocean in summer.

Source attribution and process analysis for atmospheric mercury in eastern China simulated by CMAQ-Hg

Abstract. The contribution from different emission sources and atmospheric processes to gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), particulate bound mercury (PBM) and mercury deposition in eastern China were quantified using the Community Multi-scale Air Quality (CMAQ-Hg) modeling system run with a nested domain. Natural sources (NAT) and six categories of anthropogenic mercury sources (ANTH) including cement production (CEM), domestic life (DOM), industrial boilers (IND), metal production (MET), coal-fired power plants (PP) and traffic (TRA) were considered for source apportionment. NAT were responsible for 36.6 % of annual averaged GEM concentration, which was regarded as the most important source for GEM in spite of obvious seasonal variation. Among ANTH, the influence of MET and PP on GEM were most evident especially in winter. ANTH dominated the variations of GOM and PBM concentrations with contributions of 86.7 and 79.1 %, respectively. Among ANTH, IND were the largest contributor for GOM (57.5 %) and PBM (34.4 %) so that most mercury deposition came from IND. The effect of mercury emitted from out of China was indicated by a &gt; 30 % contribution to GEM concentration and wet deposition. The contributions from nine processes – consisting of emissions (EMIS), gas-phase chemical production/loss (CHEM), horizontal advection (HADV), vertical advection (ZADV), horizontal advection (HDIF), vertical diffusion (VDIF), dry deposition (DDEP), cloud processes (CLDS) and aerosol processes (AERO) – were calculated for process analysis with their comparison in urban and non-urban regions of the Yangtze River delta (YRD). EMIS and VDIF affected surface GEM and PBM concentrations most and tended to compensate each other all the time in both urban and non-urban areas. However, DDEP was the most important removal process for GOM with 7.3 and 2.9 ng m−3 reduced in the surface of urban and non-urban areas, respectively, in 1 day. The diurnal profile variation of processes revealed the transportation of GOM from urban area to non-urban areas and the importance of CHEM/AERO in higher altitudes which partly caused diffusion of GOM downwards to non-urban areas. Most of the anthropogenic mercury was transported and diffused away from urban areas by HADV and VDIF and increased mercury concentrations in non-urban areas by HADV. Natural emissions only influenced CHEM and AERO more significantly than anthropogenic. Local emissions in the YRD contributed 8.5 % more to GEM and ~ 30 % more to GOM and PBM in urban areas compared to non-urban areas.

Measuring and modeling mercury in the atmosphere: a critical review

Abstract. Mercury (Hg) is a global health concern due to its toxicity and ubiquitous presence in the environment. Here we review current methods for measuring the forms of Hg in the atmosphere and models used to interpret these data. There are three operationally defined forms of atmospheric Hg: gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particulate bound mercury (PBM). There is relative confidence in GEM measurements (collection on a gold surface), but GOM (collection on potassium chloride (KCl)-coated denuder) and PBM (collected using various methods) are less well understood. Field and laboratory investigations suggest the methods to measure GOM and PBM are impacted by analytical interferences that vary with environmental setting (e.g., ozone, relative humidity), and GOM concentrations measured by the KCl-coated denuder can be too low by a factor of 1.6 to 12 depending on the chemical composition of GOM. The composition of GOM (e.g., HgBr2, HgCl2, HgBrOH) varies across space and time. This has important implications for refining existing measurement methods and developing new ones, model/measurement comparisons, model development, and assessing trends. Unclear features of previously published data may now be re-examined and possibly explained, which is demonstrated through a case study. Priorities for future research include identification of GOM compounds in ambient air and development of information on their chemical and physical properties and GOM and PBM calibration systems. With this information, identification of redox mechanisms and associated rate coefficients may be developed.

Use of passive sampling methods and models to understand sources of mercury deposition to high elevation sites in the Western United States.

To understand gaseous oxidized mercury (GOM) sources to the Western US, data were collected with passive samplers for ambient GOM concentrations and dry deposition at 10 sites from the coast of the Pacific Ocean to Great Basin National Park. Tests were done to better understand the samplers and the materials used. Measured dry deposition of GOM was significantly higher at sites >2000 m elevation relative to those below due to high GOM concentrations and atmospheric turbulence. At these high elevation sites, GOM dry deposition was higher in spring due to long-range transport from Asia (air parcels from the free troposphere) and some high GOM dry deposition events were related to regional emissions. Dry deposition of GOM at two sites was calculated using the passive sampler data and a multiple-resistance model. A previously developed relationship between the sampling rate of the passive sampler and GOM concentrations was used to estimate dry deposition and a scaling factor of 3 was used to adjust GOM concentrations, due to underestimation by KCl-coated denuder measurements. With the scaling factor of 3, modeled deposition was in the range of results estimated from two different models settings. However, dry deposition did not correlate consistently with either model. The disagreement could be due to uncertainties associated with measurements and/or modeling, or different GOM compounds existing in the atmosphere. If the atmospheric GOM compounds are known, dry deposition velocities could be estimated more accurately. Lastly, we investigated the potential for use of a new sampling material for GOM and checked the efficiency of the passive sampler.