Seasonal and Annual Variations in Atmospheric Hg and Pb Isotopes

Mar 2, 2017 - We present a 3-year time series of lead (Pb) and mercury (Hg) concentrations and isotope signatures in total suspended particulate (TSP)...
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Seasonal and annual variations in atmospheric Hg and Pb isotopes in Xi’an, China Hongmei Xu, Jeroen E. Sonke, Benjamin Guinot, Xuewu Fu, Ruoyu Sun, Aurelie Lanzanova, Frederic Candaudap, Zhenxing Shen, and Jun-ji Cao Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b06145 • Publication Date (Web): 02 Mar 2017 Downloaded from http://pubs.acs.org on March 5, 2017

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TOC Figure 209x151mm (150 x 150 DPI)

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Figure 1. Temporal variations of TSP and PbTSP concentrations (conc., upper panel), particulate and total gaseous Hg concentrations, and 206Pb/207Pb ratio (middle panel), and particulate and total gaseous Hg isotopes (δ202Hg, ∆199Hg) during the sampling period in Xi’an. 1044x771mm (144 x 144 DPI)

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Figure 2. Summary of published aerosol Pb (µg m-3) observations in Xi’an. Data4, 42 were made on PM2.5, whereas this study measured TSP. The ensemble of observations points at a steady decline in winter time aerosol Pb of about 5% per year over the 2003-2012 period (r2 = 0.31). 1381x677mm (144 x 144 DPI)

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Figure 3. Scatter plots of isotopic ratios of Pb (208Pb/206Pb and 206Pb/207Pb) for TSP samples collected from Nov. 2009 to Oct. 2012 in Xi’an and for potential Pb pollution sources47-50, 62-66 in China. (the Chinese Pb line was drawn using the data for major lead mines in China48). 360x263mm (96 x 96 DPI)

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Figure 4. δ202Hg and ∆199Hg signatures of TGM (●) and HgTSP (■) in Xi’an and at other locations (diverse filled symbols). The dark black striped line (∆199Hg = -0.2×δ202Hg - 0.1) represent the mixing line between the Northern Hemisphere (NH) background TGM and recent industrial TGM emissions discussed in the text. Also shown are coal samples (▲) from three Shaanxi coal mines that supply Xi’an domestic and industrial coal use18, 23, 39, 51, 52, 54-57. 303x189mm (90 x 90 DPI)

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Figure 5. a): δ202HgTGM (‰) as a function of TGM concentration (ng m-3) in Xi’an. b): linearized (1/THg) binary isotope mixing diagram between the Northern Hemispheric background TGM (■, 1.4 ng m-3; δ202HgTGM of 0.47 ± 0.45‰, 2σ) and local Xi’an urban-industrial TGM emissions, represented by Shaanxi coal (▲, δ202HgShaanxi coal of -0.67 ± 0.28‰, 2σ, and assuming no shift in δ202Hg between coal Hg and emitted TGM). 266x81mm (150 x 150 DPI)

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Seasonal and annual variations in atmospheric Hg and Pb isotopes in Xi’an, China

Hongmei Xu1,2,4, Jeroen E. Sonke3*, Benjamin Guinot4, Xuewu Fu6,3, Ruoyu Sun5,3, Aurélie Lanzanova3, Frédéric Candaudap3, Zhenxing Shen1, Junji Cao2*

1

Department of Environmental Science and Engineering, Xi’an Jiaotong University,

Xi’an, China 2

Key Lab of Aerosol Chemistry & Physics, SKLLQG, Institute of Earth Environment,

Chinese Academy of Sciences, Xi’an, China 3

Observatoire Midi-Pyrénées, Laboratoire Géosciences Environnement Toulouse,

CNRS/IRD/Université de Toulouse, France 4

Laboratoire d'Aérologie, Université de Toulouse, CNRS, UPS, France

5

Institute of Surface-Earth System Science, Tianjin University, Tianjin 300072, China

6

State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry,

Chinese Academy of Sciences, Guiyang, 550081, China

*Corresponding authors: Jeroen E. Sonke: [email protected], 14 avenue Edouard Belin, 31400 Toulouse, France, t.:+33(0)561332606, f.:+33(0)561332560; Junji Cao: [email protected], 97 Yanxiang Road, Xi’an, 710061, Shaanxi, China, t.: +86(29)62336205, f.: +86(29)62336234.

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Abstract 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 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 ∆199HgTSP averaged -0.80 ± 0.30 ‰ (1σ) and -0.02 ± 0.10 ‰ (1σ) and δ202HgTGM and ∆199HgTGM 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, while δ202HgTGM is enriched in the heavy isotopes. TSP and TGM ∆199Hg 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