Isotopic compositions of atmospheric total gaseous mercury in ten Chinese cities and implications for land surface emissions

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 ten 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 were 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 atmospheric oxidation chemistry, vegetation activity as well as residential coal combustion were not likely 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 ten Chinese cities were likely controlled by land surface emissions that were observed or reported with highly negative δ²⁰²Hg signatures.