|Affiliation(s)||PI||Project period||Funded by|
|DAS||Obrist, Daniel||08/01/2008 - 08/31/2011||National Science Foundation|
Reactive halogen compounds (RHC) can influence the tropospheric ozone (O3) budget and its oxidation capacity. RHC also have been linked to oxidation of atmospheric mercury, which can lead to atmospheric mercury depletion events (AMDE). In these events, gaseous elemental mercury [GEM] is converted to oxidized gaseous [RGM] and particulate [PHg] forms which are readily removed from the atmosphere by deposition to surfaces or particulates. The proposed study aims to elucidate atmospheric conditions and chemical pathways responsible for recently observed AMDEs at the Dead Sea in Israel. Project hypotheses include: (1) depletion of GEM at the Dead Sea is accompanied by increased levels of RGM and PHg confirming that AMDE events at the Dead Sea are analogous to those observed in the polar troposphere; (2) AMDE will be correlated with high RHC levels, specifically BrOx (Br + BrO), and detailed temporal observations along with theoretical calculations may give support for a recombination of Hg with atomic bromine as opposed to direct oxidation by bromine oxide or other oxidants; (3) observations and modeling of AMDE at the Dead Sea will show that even small concentrations of RHC may initiate GEM oxidation under certain atmospheric conditions and will allow to extrapolate the importance of oxidations to other mid-latitude marine boundary layer sites where lower RHC levels are present. These hypotheses will be tested by simultaneous measurement of speciated mercury, halogen oxides, nitrogen oxides, O3, sulfate aerosols, fine particulates, and meteorological parameters. A modeling component will be used to help identify definite mechanisms for reactive halogen chemistry and oxidation of mercury, and results will be analyzed in respect to tropospheric marine regions outside the Dead Sea. The Dead Sea, with its unusually high atmospheric RHC loads, has served as an ideal natural laboratory for study of RHC-related tropospheric chemistry such as O3 destruction resulting in formulation of new pathways and suggestion of O3 destruction across the marine boundary layer that was previously undetected but since has been confirmed.