HR: 15:25h
AN: A13F-07    [Abstracts]
TI: One-dimensional Modeling of Air-Snowpack Interactions and Bromine Activation in the Springtime Arctic Air
AU: * Toyota, K
EM: ktoyota@yorku.ca
AF: York University, Department of Earth and Space Science and Engineering, 4700 Keele St., Toronto, ON M3J 1P3 Canada
AU: McConnell, J C
EM: jcmcc@yorku.ca
AF: York University, Department of Earth and Space Science and Engineering, 4700 Keele St., Toronto, ON M3J 1P3 Canada
AB: An outbreak of reactive bromine compounds (RBCs) in the springtime Arctic boundary layer is most likely a result of halogen release to the gas phase from sea salt. Snowpack over sea ice and coastal land area should serve as an efficient reactor to produce RBCs via heterogeneous reactions taking place in between snowpack interstitial air and the surface of snow grains, once sea-salt aerosols and/or frost flowers are deposited or buried into snowpack. To examine the role of snowpack in bromine explosion and ozone depletions in the Arctic boundary layer, we have developed a one-dimensional air-snowpack chemical-transport model describing relevant processes including multiphase reactions in snow grains and snowpack interstitial air. For the transport of gaseous compounds in between snowpack and overlying air, we consider not only molecular diffusion but also wind pumping. Actinic flux is attenuated with depth in snowpack but still capable of driving autocatalytic bromine release within the snowpack system. In 5-day runs for late April at 80°N latitude, BrO mixing ratios in snowpack interstitial air are simulated to reach higher than 100 pmol/mol. This results in a significant decrease in ozone mixing ratio with depth and its diurnal variations in the interstitial air, both of which agree with recent observational findings. We found that wind pumping makes ozone import from overlying air efficient, thereby promotes autocatalytic bromine release within snowpack, and eventually increases the amount of RBCs exported to the atmosphere. Even without the heterogeneous recycling of inorganic halogens on atmospheric aerosols, the total mixing ratio of inorganic bromines can reach 100 pmol/mol in the 400-m deep boundary layer after buildup for 5 days at 10 m/s wind speed with the snowpack bromide concentration of 3 μM (the highest end of observed range). Enhancement in the mixing ratios of nitrogen oxides and volatile organic compounds in the interstitial air by photochemical release from snow grains also exerts a significant influence on bromine activation.
DE: 0322 Constituent sources and sinks
DE: 0365 Troposphere: composition and chemistry
DE: 0736 Snow (1827, 1863)
DE: 0750 Sea ice (4540)
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005