Seasonal and Annual Variations in Atmospheric Hg and Pb Isotopes in Xi'an, China

摘要

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~(-3)), Pb_(TSP) (0.33 ± 0.15 μg m~(-3)) and Hg_(TSP) (0.64 ± 0.54 ng m~(-3)), and TGM (5.7 ± 2.7 ng m"3) 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. δ~(202)Hg_(TSP) and △~(199)Hg_(TSP) averaged -0.80 ± 0.30‰ (1σ) and -0.02 ± 0.10‰ (1σ) and δ~(202)Hg_(TGM) and ∆~(199)Hg_(TGM) averaged -0.08 ± 0.41‰ (1σ) and 0.00 ± 0.04‰ (1σ). Relative to raw coal from Shaanxi and surrounding provinces, δ~(202)Hg_(Tsp) is enriched in the light Hg isotopes, whereas δ~(202)Hg_(TGM) is enriched in the heavy isotopes. TSP and TGM ∆~(199)Hg signatures are indistinguishable from raw coal, indicating little photochemical mass independent fractionation of atmospheric Hg in the near-field urban-industrial environment. δ~(202)Hg_(TGM) correlates significandy with TGM levels (r~2 = 0.3, p < 0.01) and likely reflects binary mixing of local industrial TGM emissions with global background TGM.