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

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), PbTSP (0.33 ± 0.15 μg m–3) and HgTSP (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. δ202HgTSP and Δ199HgTSP averaged −0.80 ± 0.30‰ (1σ) and −0.02
± 0.10‰ (1σ) and δ202HgTGM and Δ199HgTGM averaged −0.08
± 0.41‰ (1σ) and 0.00 ± 0.04‰ (1σ).
Relative to raw coal from Shaanxi and surrounding provinces, δ202HgTSP is enriched in the light Hg isotopes, whereas
δ202HgTGM is enriched in the heavy isotopes.
TSP and TGM Δ199Hg signatures are indistinguishable
from raw coal, indicating little photochemical mass independent fractionation
of atmospheric Hg in the near-field urban-industrial environment.
δ202HgTGM correlates significantly with
TGM levels (r2 = 0.3, p < 0.01) and likely reflects binary mixing of local industrial
TGM emissions with global background TGM.