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dc.contributor.authorShah, V.
dc.contributor.authorGratz, L. E.
dc.contributor.authorAmbrose, J. L.
dc.contributor.authorJaffe, D. A.
dc.contributor.authorCampos, T. L.
dc.contributor.authorFlocke, F. M.
dc.contributor.authorReeves, M.
dc.contributor.authorStechman, D.
dc.contributor.authorStell, M.
dc.contributor.authorFesta, J.
dc.contributor.authorStutz, J.
dc.contributor.authorWeinheimer, A. J.
dc.contributor.authorKnapp, D. J.
dc.contributor.authorMontzka, D. D.
dc.contributor.authorTyndall, G. S.
dc.contributor.authorApel, E. C.
dc.contributor.authorHornbrook, R. S.
dc.contributor.authorHills, A. J.
dc.contributor.authorRiemer, D. D.
dc.contributor.authorBlake, N. J.
dc.contributor.authorCantrell, C. A.
dc.contributor.authorMauldin III, R. L.
dc.contributor.authorJaegle, L.
dc.contributor.authorSelin, Noelle E
dc.contributor.authorSong, Sanquan
dc.date.accessioned2016-05-23T16:55:02Z
dc.date.available2016-05-23T16:55:02Z
dc.date.issued2016-02
dc.date.submitted2016-01
dc.identifier.issn1680-7324
dc.identifier.issn1680-7316
dc.identifier.urihttp://hdl.handle.net/1721.1/102625
dc.description.abstractWe collected mercury observations as part of the Nitrogen, Oxidants, Mercury, and Aerosol Distributions, Sources, and Sinks (NOMADSS) aircraft campaign over the southeastern US between 1 June and 15 July 2013. We use the GEOS-Chem chemical transport model to interpret these observations and place new constraints on bromine radical initiated mercury oxidation chemistry in the free troposphere. We find that the model reproduces the observed mean concentration of total atmospheric mercury (THg) (observations: 1.49 ± 0.16 ng m[superscript −3], model: 1.51 ± 0.08 ng m[superscript −3]), as well as the vertical profile of THg. The majority (65 %) of observations of oxidized mercury (Hg(II)) were below the instrument's detection limit (detection limit per flight: 58–228 pg m[superscript −3]), consistent with model-calculated Hg(II) concentrations of 0–196 pg m[superscript −3]. However, for observations above the detection limit we find that modeled Hg(II) concentrations are a factor of 3 too low (observations: 212 ± 112 pg m[superscript −3], model: 67 ± 44 pg m[superscript −3]). The highest Hg(II) concentrations, 300–680 pg m[superscript −3], were observed in dry (RH  <  35 %) and clean air masses during two flights over Texas at 5–7 km altitude and off the North Carolina coast at 1–3 km. The GEOS-Chem model, back trajectories and observed chemical tracers for these air masses indicate subsidence and transport from the upper and middle troposphere of the subtropical anticyclones, where fast oxidation of elemental mercury (Hg(0)) to Hg(II) and lack of Hg(II) removal lead to efficient accumulation of Hg(II). We hypothesize that the most likely explanation for the model bias is a systematic underestimate of the Hg(0) + Br reaction rate. We find that sensitivity simulations with tripled bromine radical concentrations or a faster oxidation rate constant for Hg(0) + Br, result in 1.5–2 times higher modeled Hg(II) concentrations and improved agreement with the observations. The modeled tropospheric lifetime of Hg(0) against oxidation to Hg(II) decreases from 5 months in the base simulation to 2.8–1.2 months in our sensitivity simulations. In order to maintain the modeled global burden of THg, we need to increase the in-cloud reduction of Hg(II), thus leading to faster chemical cycling between Hg(0) and Hg(II). Observations and model results for the NOMADSS campaign suggest that the subtropical anticyclones are significant global sources of Hg(II).en_US
dc.description.sponsorshipNational Science Foundation (U.S.) (Grant 1217010)en_US
dc.language.isoen_US
dc.publisherCopernicus GmbHen_US
dc.relation.isversionofhttp://dx.doi.org/10.5194/acp-16-1511-2016en_US
dc.rightsCreative Commons Attributionen_US
dc.rights.urihttp://creativecommons.org/licenses/by/3.0/en_US
dc.sourceCopernicus Publicationsen_US
dc.titleOrigin of oxidized mercury in the summertime free troposphere over the southeastern USen_US
dc.typeArticleen_US
dc.identifier.citationShah, V., L. Jaegle, L. E. Gratz, J. L. Ambrose, D. A. Jaffe, N. E. Selin, S. Song, et al. “Origin of Oxidized Mercury in the Summertime Free Troposphere over the Southeastern US.” Atmos. Chem. Phys. 16, no. 3 (February 10, 2016): 1511–1530.en_US
dc.contributor.departmentMassachusetts Institute of Technology. Institute for Data, Systems, and Societyen_US
dc.contributor.departmentMassachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciencesen_US
dc.contributor.mitauthorSelin, Noelle Eckleyen_US
dc.contributor.mitauthorSong, Shaojieen_US
dc.relation.journalAtmospheric Chemistry and Physicsen_US
dc.eprint.versionFinal published versionen_US
dc.type.urihttp://purl.org/eprint/type/JournalArticleen_US
eprint.statushttp://purl.org/eprint/status/PeerRevieweden_US
dspace.orderedauthorsShah, V.; Jaegle, L.; Gratz, L. E.; Ambrose, J. L.; Jaffe, D. A.; Selin, N. E.; Song, S.; Campos, T. L.; Flocke, F. M.; Reeves, M.; Stechman, D.; Stell, M.; Festa, J.; Stutz, J.; Weinheimer, A. J.; Knapp, D. J.; Montzka, D. D.; Tyndall, G. S.; Apel, E. C.; Hornbrook, R. S.; Hills, A. J.; Riemer, D. D.; Blake, N. J.; Cantrell, C. A.; Mauldin III, R. L.en_US
dspace.embargo.termsNen_US
dc.identifier.orcidhttps://orcid.org/0000-0002-6396-5622
mit.licensePUBLISHER_CCen_US


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