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Isotopic composition of atmospheric particulate bound mercury (PBM) was obtained at four remote sites in different geographical regions of China for three to 12 month periods. Mean (±1σ) Δ 199 Hg PBM was the highest at the site in southwestern China (0.66 ± 0.32‰), followed by the site in northeastern China (0.36 ± 0.34‰), the site in the marine boundary layer of East China Sea (0.35 ± 0.33‰), and was the lowest at the site in northwestern China (0.27 ± 0.22‰). Δ 199 Hg PBM was relatively higher in cold than warm season at the sites in northwestern and southwestern China, whereas the opposite was found at the site in northeastern China. We propose that the seasonal variations of Δ 199 Hg PBM were influenced by the exposure of air masses to regional (e.g., anthropogenic and dust related) and long-range (e.g., anthropogenic and oceanic) sources in the preceding several days, with the former characterized by lower Δ 199 Hg PBM and the latter characterized by more positive Δ 199 Hg PBM due to sufficient atmospheric transformations. Modeling results from Potential Source Contribution Function suggested that domestic anthropogenic emission was the major contributor to PBM pollution at the sites in northeastern and eastern China, whereas long-range transboundary transport of PBM from South Asia played a more important role at the sites in southwestern and northwestern China.

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/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.

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Rice, one of the most widely cultivated crops, has received great attention in contaminant uptake from soil and air, especially for the special approaches used for its cultivation. The dry−wet alternation method can influence the air−soil partitioning of semivolatile organic compounds (SVOCs) in the paddy ecosystem. Here, we modified a fugacity sampler to investigate the air−surface in situ partitioning of ubiquitous polycyclic aromatic hydrocarbons (PAHs) at different growth stages in a suburban paddy field in South China. The canopy of rice can form a closed space, which acts like a chamber that can force the air under the canopy to equilibrate with the field surface. When we compared the fugacities calculated using a fugacity model of the partition coefficients to the measured fugacities, we observed similar trends in the variation, but significantly different values between different growing stages, especially during the flooding stages. However, the measured and calculated fugacity fractions were comparable when uncertainties in our calculations were considered, with the exception of the high molecular weight (HMW) PAHs. The measured fugacity fractions suggested that the HMW PAHs were also closed to equilibrium between the paddy field and atmosphere. The modified fugacity sampler provided a novel way of accurately determining the in situ air−soil partitioning of SVOCs in a wet paddy field.