| Summary: | Dissertation (Ph.D.) University of Alaska Fairbanks, 2021 During late winter and spring in the Arctic, unique chemistry produces high levels of reactive bromine radicals (e.g., bromine atomic radicals and bromine monoxide, BrO) in the lower troposphere. These high levels of bromine radicals react with and reduce ambient ozone and oxidize gaseous elemental mercury. These reactive bromine species are chemically released from frozen saline surfaces and are affected by meteorological processes such as transport and mixing. Prior work has proposed that heterogenous reactions on snowpack surfaces as well as on atmospheric particle surfaces contribute to the reactive bromine production. We investigate these hypotheses using an extensive dataset of lower-tropospheric BrO observations from the Arctic Ocean and Utqiaġvik (formerly Barrow). First, we combine BrO observations with meteorological data and use principal component analysis to determine what environmental processes are correlated with BrO. We find that increased levels of reactive bromine under two sets of meteorological conditions: 1) stable, poorly vertically mixed conditions with temperature inversions, and 2) low-atmospheric-pressure conditions with increased vertical mixing. A principal component regression model based on these correlations predicted both the vertical column density of BrO in the lowest 2 km of the troposphere (R = 0.45) and the vertical column density of BrO in the lowest 200 m (R = 0.54). Next, we compare BrO observations to a global chemicaltransport model, GEOS-Chem, which was recently modified to add a blowing snow sea salt aerosol particle source. The GEOS-Chem model including the blowing snow process predicts monthly averaged BrO within experimental error for 9 of 13 total months of observations in Spring 2015 but cannot replicate hourly peaks in observed BrO. The model also predicts BrO during the Fall, which is not supported by the observations, potentially indicating a problem with the blowing snow model. We improve GEOS-Chem ...
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