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dc.contributor.authorSwanson, William
dc.date.accessioned2021-12-17T20:11:37Z
dc.date.available2021-12-17T20:11:37Z
dc.date.issued2021-08
dc.identifier.urihttp://hdl.handle.net/11122/12633
dc.descriptionThesis (Ph.D.) University of Alaska Fairbanks, 2021en_US
dc.description.abstractDuring 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 by adding a snowpack source of molecular bromine arising from deposition of precursor species such as ozone. Adding this snowpack molecular bromine source improves the agreement between the model and the observed monthly BrO at Utqiaġvik. However, a prior literature form of this model that had assumed an increased daytime yield of molecular bromine due to photochemistry leads to overprediction of radical bromine and is not supported. We find that using both the blowing snow aerosol particle source and the snowpack molecular bromine source together in GEOS-Chem increases model skill in simulating Arctic reactive bromine events. Our global chemical model improvements should improve prediction of the effect of climate change on Arctic reactive bromine levels and help assess their implications for ozone depletion and mercury deposition.en_US
dc.description.sponsorshipNational Science Foundation grants ARC-1602716 and ARC-1602883, NASA Earth and Space Science Fellowship Program grant 80NSSC17K0361ren_US
dc.description.tableofcontentsChapter 1: Introduction -- Chapter 2: Arctic reactive bromine events occur in two distinct sets of environmental conditions: a statistical analysis of six years of observations -- Chapter 3: Comparison of GEOS-Chem modeled Arctic tropospheric bromine monoxide events using a blowing snow source and observations from MAX-DOAS -- Chapter 4: Modeling reactive bromine in GEOS-Chem with both a blowing snow source and a snowpack source -- Chapter 5: Conclusions, Implications and Future Outlook -- Appendices.en_US
dc.language.isoen_USen_US
dc.subjectBromineen_US
dc.subjectArctic Oceanen_US
dc.subjectMeteorologyen_US
dc.subjectAtmospheric chemistryen_US
dc.subjectTropospheric chemistryen_US
dc.subjectAtmospheric aerosolsen_US
dc.subjectAtmospheric chlorine compoundsen_US
dc.subject.otherDoctor of Philosophy in Environmental Chemistryen_US
dc.titleTropospheric reactive bromine and meteorology over the Arctic Oceanen_US
dc.typeThesisen_US
dc.type.degreephden_US
dc.identifier.departmentDepartment of Chemistry and Biochemistryen_US
dc.contributor.chairSimpson, William
dc.contributor.committeeGuerard, Jennifer
dc.contributor.committeeTrainor, Thomas
dc.contributor.committeeMao, Jingqiu
refterms.dateFOA2021-12-17T20:11:38Z


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