HR: 10:40h
AN: A22C-02    [Abstracts]
TI: Observations of High-latitude NOx Removal Processes: The Roles of Dinitrogen Pentoxide, Aerosols, and Seasonal Snow Pack
AU: * Apodaca, R L
EM: ftrla@uaf.edu
AF: Geophysical Institute and Department of Chemistry and Biochemistry University of Alaska Fairbanks, 903 Koyukuk Drive, Fairbanks, AK 99775,
AU: Huff, D M
EM: fsdmh22@uaf.edu
AF: Geophysical Institute and Department of Chemistry and Biochemistry University of Alaska Fairbanks, 903 Koyukuk Drive, Fairbanks, AK 99775,
AU: Cahill, C F
EM: ffcfc@uaf.edu
AF: Geophysical Institute and Department of Chemistry and Biochemistry University of Alaska Fairbanks, 903 Koyukuk Drive, Fairbanks, AK 99775,
AU: Simpson, W R
EM: ffwrs@uaf.edu
AF: Geophysical Institute and Department of Chemistry and Biochemistry University of Alaska Fairbanks, 903 Koyukuk Drive, Fairbanks, AK 99775,
AB: Heterogeneous chemistry of dinitrogen pentoxide (N₂O₅) plays a major role in the removal of nitrogen oxides (NO_x = NO + NO₂), particularly in the cold, dark nighttime atmosphere in winters at high latitudes. NO_x is ultimately converted to nitric acid, which, in turn, is deposited to surfaces. The resultant nitric acid deposition has unintended consequences, such as nitrogen fertilization and acidification of sensitive ecosystems. As anthropogenic emissions increase globally, and particularly in high latitudes, the importance of a mechanistic understanding of NO_x removal processes and their impact on sensitive ecosystems, becomes more important for assessing fate of this pollution. We report measurements of the sum of NO₃ and N₂O₅ (primarily N₂O₅ at ambient temperatures) in the Fairbanks, AK pollution plume during a two week period in March 2007. Ancillary atmospheric observations include NO, NO₂, and O₃-levels, aerosol particle size distribution, and aerosol elemental composition. N₂O₅ loss to snow pack was observed by measuring boundary layer profiles and chemical composition of the snow. The profiles were conducted by sampling the boundary-layer gradient at 1 and 4 meter altitudes. Results show elevated levels of nitrate ion in the snow pack, typical nighttime lifetimes for N₂O₅ between 10 and 20 minutes, and periods of clear vertical gradients in N₂O₅. The reported lifetimes are short when compared to observations from lower latitudes and most nights demonstrate rapid decay of N₂O₅ prior to sunrise; both phenomena occur in air masses without measurable NO. It is of particular interest that when gradients were present, N₂O₅ mixing ratios typically increased with elevation, but periods were observed where mixing ratios would decrease with elevation. Implications of the short lifetimes, rapid decay of N₂O₅ in highly polluted air masses, and gradient observations are discussed, and suggest that deposition to the surface competed with reactions in the atmosphere during the study. These observations provide a foundation for developing a mechanistic understanding of the NO_x removal pathways at high latitudes.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0365 Troposphere: composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting