The isotopic composition of atmospheric total gaseous mercury (TGM) and particle-bound mercury (PBM) and mercury (Hg) in litterfall samples have been determined at urban/industrialized and rural sites distributed over mainland China for identifying Hg sources and transformation processes. TGM and PBM near anthropogenic emission sources display negative δ(202)Hg and near-zero Δ(199)Hg in contrast to relatively positive δ(202)Hg and negative Δ(199)Hg observed in remote regions, suggesting that different sources and atmospheric processes force the mass-dependent fractionation (MDF) and mass-independent fractionation (MIF) in the air samples. Both MDF and MIF occur during the uptake of atmospheric Hg by plants, resulting in negative δ(202)Hg and Δ(199)Hg observed in litter-bound Hg. The linear regression resulting from the scatter plot relating the δ(202)Hg to Δ(199)Hg data in the TGM samples indicates distinct anthropogenic or natural influences at the three study sites. A similar trend was also observed for Hg accumulated in broadleaved deciduous forest foliage grown in areas influenced by anthropogenic emissions. The relatively negative MIF in litter-bound Hg compared to TGM is likely a result of the photochemical reactions of Hg(2+) in foliage. This study demonstrates the diagnostic stable Hg isotopic composition characteristics for separating atmospheric Hg of different source origins in China and provides the isotopic fractionation clues for the study of Hg bioaccumulation.

We present a 3-year time series of lead (Pb) and mercury (Hg) concentrations and isotope signatures in total suspended particulate (TSP) matter and as total gaseous Hg (TGM) in Xi'an, Northwestern China. Mean concentrations of TSP (299 ± 120 μg m), Pb (0.33 ± 0.15 μg m) and Hg (0.64 ± 0.54 ng m), and TGM (5.7 ± 2.7 ng m) were elevated. We find that atmospheric Pb levels in winter in Xi'an have decreased by 4.6% per year since 2003, yet remain elevated relative to air quality guidelines and therefore a major health concern. δHg and ΔHg averaged -0.80 ± 0.30‰ (1σ) and -0.02 ± 0.10‰ (1σ) and δHg and ΔHg averaged -0.08 ± 0.41‰ (1σ) and 0.00 ± 0.04‰ (1σ). Relative to raw coal from Shaanxi and surrounding provinces, δHg is enriched in the light Hg isotopes, whereas δHg is enriched in the heavy isotopes. TSP and TGM ΔHg signatures are indistinguishable from raw coal, indicating little photochemical mass independent fractionation of atmospheric Hg in the near-field urban-industrial environment. δHg correlates significantly with TGM levels (r = 0.3, p < 0.01) and likely reflects binary mixing of local industrial TGM emissions with global background TGM.