Domestic and Transboundary Sources of Atmospheric Particulate Bound Mercury in Remote Areas of China: Evidence from Mercury Isotopes

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 ( 16) Delta Hg-199(PBM) was the highest at the site in southwestern China (0.66 +/- 0.32 parts per thousand), followed by the site in northeastern China (0.36 +/- 0.34 parts per thousand), the site in the marine boundary layer of East China Sea (0.35 +/- 0.33 parts per thousand), and was the lowest at the site in northwestern China (0.27 +/- 0.22 parts per thousand). Delta Hg-199(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 Delta Hg-199(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 Delta Hg-199(PBM) and the latter characterized by more positive Delta Hg-199(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.