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Intellectual Merit
This project will study how oxides of nitrogen mediate the halogen chemistry that occurs in Polar marine environments. It is known that in Polar Regions in spring time, both ozone and mercury in the near-surface atmosphere are rapidly consumed; in the case of ozone it can be completely removed. Mercury is converted to more adsorptive and/or particulate forms that then deposit to the surface, where these products can impact the biosphere. This atmospheric phenomenon is likely to be highly affected by nitrogen oxides (NOx), which are anthropogenic pollutants Therefore, changes in high-latitude NOx emissions may be indirect controls on the fate of ozone and other pollutants in the Polar Regions. Bromine released from sea salt is probably the key the reactive species that consumes ozone and mercury, however the chemical mechanisms for bromide salt oxidation to produce reactive bromine are not clearly determined. Several bromine activation mechanisms have been suggested, and that are known to occur in the aboratory, involve oxides of nitrogen, either NO2 or N2O5. Furthermore, once the chain reaction involving Br atoms and BrO radicals is initiated, the chain carriers may be sequestered by reactions involving NOx, e.g. via BrO reaction with NO2. The well-known “bromine explosion” can also be impacted through formation of peroxynitric acid, which reduces HO2, a key species in the bromine explosion chemistry. We are proposing here to systematically investigate the NOx-dependence of bromine activation and the bromine explosion chemistry by taking advantage of the several order of magnitude variation of [NOx] that is present in the plume emanating from the oil fields at Prudhoe Bay, on Alaska’s North Slope. We propose to conduct aircraft-based measurement campaigns in the Fall of 2007 and the Spring of 2008 to pursue this question, by flying in and out of the Prudhoe emission plume, as the plume moves downwind. Flying across the plume, we will encounter a wide range of [NOx], at what should be relatively constant sea salt aerosol concentrations. We propose to conduct measurements of BrO using a MAX-DOAS instrument mounted in the aircraft, as well as NOx and NOy, N2O5, O3, and sea salt aerosol. Cl-, Br-, NO3 -, and SO4 = will be determined in the aerosol particles via filter sampling and ion chromatographic analysis. The instrumentation will be installed in the Purdue ALAR aircraft, which will be based from Barrow, AK. The flights will begin at Deadhorse, AK, and follow the plume over a range of NOx conditions in the Arctic spring, when bromine explosions frequently occur in the North Slope region. This work represents a unique combination of affordable aircraft logistics, state-of-the-science measurement techniques, and an excellent opportunity to examine Arctic halogen chemistry under a wide range of NOx conditions.
Broader Impacts
This project aims to improve our understanding of the remarkable atmospheric chemical changes that occur in springtime in the Arctic. These are known to substantially alter the composition of the atmosphere, e.g. producing Arctic haze and depositing mercury. As the Arctic surface (i.e. snow and sea ice cover) changes due to climate change, this chemistry and thus atmospheric composition will change in as yet poorly understood ways. This proposed work is thus a part of the badly needed work in understanding polar atmospheric chemistry and connections to climate change. This work involves the training of both graduate and undergraduate students, as well as interactions with high school students in the North Slope Borough. We plan to conduct several “school yard” public talks, and high school presentations to Inupiat Eskimo students during the course of this project, in coordination with our contacts with the Inupiat community in Barrow. The ALAR aircraft will incorporate a camera for film clips and photographs documenting the science, which will be incorporated into a web log that will be designed to communicate in plain language, the significance of our work.
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