Abstract Characterizing 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/m 3 , 26 ± 38 pg/m 3 , and 8 ± 10 pg/m 3 , 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 δ 202 Hg (−1.63‰ to 0.34‰) and Δ 199 Hg (−0.26‰ to −0.02‰). GEM δ 202 Hg and Δ 199 Hg 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 δ 202 Hg (−1.79 ± 0.24‰, 1σ) and near‐zero Δ 199 Hg (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.
Abstract. Reliable quantification of air–surface fluxes of elemental Hg vapor (Hg0) is crucial for understanding mercury (Hg) global biogeochemical cycles. There have been extensive measurements and modeling efforts devoted to estimating the exchange fluxes between the atmosphere and various surfaces (e.g., soil, canopies, water, snow, etc.) in the past three decades. However, large uncertainties remain due to the complexity of Hg0 bidirectional exchange, limitations of flux quantification techniques and challenges in model parameterization. In this study, we provide a critical review on the state of science in the atmosphere–surface exchange of Hg0. Specifically, the advancement of flux quantification techniques, mechanisms in driving the air–surface Hg exchange and modeling efforts are presented. Due to the semi-volatile nature of Hg0 and redox transformation of Hg in environmental media, Hg deposition and evasion are influenced by multiple environmental variables including seasonality, vegetative coverage and its life cycle, temperature, light, moisture, atmospheric turbulence and the presence of reactants (e.g., O3, radicals, etc.). However, the effects of these processes on flux have not been fundamentally and quantitatively determined, which limits the accuracy of flux modeling. We compile an up-to-date global observational flux database and discuss the implication of flux data on the global Hg budget. Mean Hg0 fluxes obtained by micrometeorological measurements do not appear to be significantly greater than the fluxes measured by dynamic flux chamber methods over unpolluted surfaces (p = 0.16, one-tailed, Mann–Whitney U test). The spatiotemporal coverage of existing Hg0 flux measurements is highly heterogeneous with large data gaps existing in multiple continents (Africa, South Asia, Middle East, South America and Australia). The magnitude of the evasion flux is strongly enhanced by human activities, particularly at contaminated sites. Hg0 flux observations in East Asia are comparatively larger in magnitude than the rest of the world, suggesting substantial re-emission of previously deposited mercury from anthropogenic sources. The Hg0 exchange over pristine surfaces (e.g., background soil and water) and vegetation needs better constraints for global analyses of the atmospheric Hg budget. The existing knowledge gap and the associated research needs for future measurements and modeling efforts for the air–surface exchange of Hg0 are discussed.
Lead (Pb) emissions into the atmosphere from anthropogenic sources have attracted considerable attention due to lead's high toxicity and associated human health and environmental impacts. Pb emission inventories need to be updated considering the development of modern industry as well as the transformation and upgrading of industrial equipment in recent years. Coal-fired power plants (CFPPs) have been an important source of atmospheric Pb emission in China since the late 1990s, while tremendous advantages have been achieved in the air-pollution control devices (APCDs) in the most recent two decades. In this study, Pb emissions from eight CFPPs, two of which have circulating fluidized bed boilers (CFB) and the others have pulverized coal fired boilers (PC), in Guizhou province, Southwest China were investigated. Solid samples including feed fuel (coal, gangue, and coal slime), limestone, bottom ash, fly ash, and gypsum, as well as stack flue gas samples were simultaneously collected for determining the internal partitioning behavior and the atmospheric emissions of Pb from these CFPPs. Pb concentrations of feed coal, limestone, bottom ash, fly ash, gypsum, and stack flue gas were in the range of 10.17–30.94, 0.36–3.08, 7.75–27.10, 33.56–73.16, 0.34–2.18 mg·kg–1, and 0.33–1.58 μg·Nm−3, respectively. The mass balance (output/input) ratio of Pb was in the range of 83.73–124.95%, with input dominated by the feed coal (95.89–99.96%) and output by fly ash (73.17–97.54%), followed by bottom ash (2.16–26.76%) and atmospheric emissions (0.01–0.08%). More Pb ended up in PC fly ash (88.89–97.54%) than CFB fly ash (73.17–81.19%), but an opposite trend was found in the bottom ash for different boilers. Pb emission factors (EMFs) could not be differentiated significantly between PC and CFB boilers, which were in the range of 2.32–10.67 mg·t–1 fuel, 1.28–6.51 μg·(kW·h)−1, or 0.12–0.51 g·TJ–1. Atmospheric Pb emissions from Guizhou's CFPP were estimated to be 430 ± 163 kg·y–1 in 2017, much lower than previously reported values.
Abstract. To better understand the influence of monsoonal climate and transport of atmospheric mercury (Hg) in southwestern China, measurements of total gaseous mercury (TGM, defined as the sum of gaseous elemental mercury, GEM, and gaseous oxidized mercury, GOM), particulate bound mercury (PBM) and GOM were carried out at Ailaoshan Station (ALS, 2450 m a.s.l.) in southwestern China from May 2011 to May 2012. The mean concentrations (± SD) for TGM, GOM and PBM were 2.09 ± 0.63, 2.2 ± 2.3 and 31.3 ± 28.4 pg m−3, respectively. TGM showed a monsoonal distribution pattern with relatively higher concentrations (2.22 ± 0.58 ng m−3, p = 0.021) during the Indian summer monsoon (ISM, from May to September) and the east Asia summer monsoon (EASM, from May to September) periods than that (1.99 ± 0.66 ng m−3) in the non-ISM period. Similarly, GOM and PBM concentrations were higher during the ISM period than during the non-ISM period. This study suggests that the ISM and the EASM have a strong impact on long-range and transboundary transport of Hg between southwestern China and south and southeast Asia. Several high TGM events were accompanied by the occurrence of northern wind during the ISM period, indicating anthropogenic Hg emissions from inland China could rapidly increase TGM levels at ALS due to strengthening of the EASM. Most of the TGM and PBM events occurred at ALS during the non-ISM period. Meanwhile, high CO concentrations were also observed at ALS, indicating that a strong south tributary of westerlies could have transported Hg from south and southeast Asia to southwestern China during the non-ISM period. The biomass burning in southeast Asia and anthropogenic Hg emissions from south Asia are thought to be the source of atmospheric Hg in remote areas of southwestern China during the non-ISM period.
Abstract. Land surface emissions are an important source of atmospheric total gaseous mercury (TGM); however, its role on the variations of TGM isotopic compositions and concentrations has not been properly evaluated. In this study, TGM isotope compositions, a powerful tracer for sources and transformation of Hg, were measured at 10 urban sites and one rural site in China. TGM concentrations were higher in summer than in winter in most cities except in Guiyang and Guangzhou in the low latitudes. The summertime high TGM concentrations coincided with prevailing low TGM δ202Hg and high TGM Δ199Hg signatures. These seasonal patterns were in contrast with those typically observed in rural areas in the Northern Hemisphere, suggesting that atmospheric oxidation chemistry, vegetation activity and residential coal combustion were likely not the dominant mechanisms contributing to the TGM concentration and isotopic composition seasonality in Chinese cities. The amplitudes of seasonal variations in TGM concentrations and Δ199Hg (or TGM δ202Hg) were significantly positively (or negatively) correlated with that of the simulated soil GEM emission flux. These results suggest that the seasonal variations in TGM isotopic compositions and concentrations in the 10 Chinese cities were likely controlled by land surface emissions that were observed or reported with highly negative δ202Hg signatures.
Abstract Oceanic emission of gaseous elemental mercury (Hg 0 or GEM) is an important source for atmospheric mercury (Hg), but existing estimates of global gross oceanic Hg 0 emissions are highly variable (800–7,220 Mg yr −1 ). This study measured atmospheric GEM concentrations and isotopic compositions at two coastal sites in Terengganu, Malaysia, a region that receives air masses from both hemispheres, during 2019–2021 to diagnose the amount of oceanic Hg 0 emissions. Significantly lower mean (±1sd) concentration (1.28 ± 0.20 ng m −3 ), Δ 199 Hg (−0.23 ± 0.03‰), and Δ 200 Hg (−0.066 ± 0.018‰) and significantly higher δ 202 Hg (0.43 ± 0.12‰) were observed during the wet season when air masses were predominantly from the Southern Hemisphere, compared with those (mean concentration, Δ 199 Hg, Δ 200 Hg, and δ 202 Hg of 1.77 ± 0.09 ng m −3 , −0.17 ± 0.03‰, −0.045 ± 0.023‰, and 0.25 ± 0.11‰, respectively) during the dry season when air masses were predominantly from the Northern Hemisphere, suggesting interhemispheric difference in GEM concentrations and its isotopic compositions. Using a Δ 200 Hg mass balance model, we estimated that the oceanic Hg 0 emissions from Hg II reduction should be below 2,250 ± 891 Mg yr −1 (±1sd), which is at the low‐end range of the literature reported values. We then used the constrained value as emission input to a three‐dimensional atmospheric Hg isotope model and reproduced well the global distributions and interhemispheric gradient of atmospheric GEM Δ 200 Hg. The findings from the present study will help to better understand Hg 0 emissions from global oceans and their roles in global atmospheric Hg cycling.
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