Isotopic compositions of atmospheric total gaseous mercury in 10 Chinese cities and implications for land surface emissions

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 delta Hg-202 and high TGM Delta Hg-199 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 Delta Hg-199 (or TGM delta Hg-202) 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 delta Hg-202 signatures.

Automated summary

The study found that the seasonal variations in TGM isotopic compositions and concentrations in 10 Chinese cities were likely controlled by land surface emissions with highly negative delta Hg-202 signatures, rather than atmospheric oxidation chemistry, vegetation activity, or residential coal combustion. The amplitudes of seasonal variations in TGM concentrations and Delta Hg-199 were significantly correlated with the simulated soil GEM emission flux.