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Arctic mercury depletion and its quantitative link with halogens |
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| Authors: | Huiting Mao Robert W Talbot Barkley C Sive Su Youn Kim Donald R Blake Andrew J Weinheimer |
| Institution: | 1. Department of Chemistry, State University of New York College of Environmental Science and Forestry, One Forestry Drive, Syracuse, New York, 13210, USA 2. Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX, 77204–5007, USA 3. Institute for the Study of Earth, Oceans, and Space, Climate Change Research Center, University of New Hampshire, Morse Hall, 8 College Road, Durham, NH, 03824, USA 4. Department of Soil, Water, and Climate, University of Minnesota, St. Paul, MN, 55108–6028, USA 5. Department of Chemistry, University of California – Irvine, Irvine, CA, 92697–2025, USA 6. National Center for Atmospheric Research, Earth and Sun Systems Laboratory, P.O. Box?3000, Boulder, CO, 80307–3000, USA |
| Abstract: | Gas phase elemental mercury (Hg°) was measured aboard the NASA DC-8 research aircraft during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) campaign conducted in spring 2008 primarily over the North American Arctic. We examined the vertical distributions of Hg° and ozone (O3) together with tetrachloroethylene (C2Cl4), ethyne (C2H2), and alkanes when Hg°- and O3-depleted air masses were sampled near the surface (<1 km). This study suggests that Hg° and O3 depletions commonly occur over linear distances of ~20–200 km. Horizontally there was a sharp decreasing gradient of ~100 ppqv in Hg° over <10 km in going from the bay near Ellesmere Island to the frozen open ocean. There was a distinct land-ocean difference in the vertical thickness of the Hg°-depleted layer – being variable but around a few 100 meters over the ocean whereas occurring only very near the surface over land. Data support that atmospheric mercury depletion events are driven by Hg° reactions with halogen atoms. Derived from data collected aboard the DC-8, we present mathematical expressions giving the rates of Hg° and O3 depletions as a function of the radical concentrations. These relationships can be a useful metric to evaluate models that attempt to reproduce springtime Arctic Hg° and/or O3 depletion events, and they can also be employed to obtain order-of-magnitude estimates of radical concentrations and the ratio Br]/Cl]. |
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