HR: 0800h
AN: A21C-0878    [Abstracts]
TI: A Trajectory Study Into the Origin of Spring Time Arctic Boundary Layer Ozone Depletion
AU: Chan, E
EM: Elton.Chan@ec.gc.ca
AF: Environment Canada, Air Quality Research Branch, 4905 Dufferin Street, Toronto, ON M3H 5T4 Canada
AU: * Bottenheim, J W
EM: Jan.Bottenheim@ec.gc.ca
AF: Environment Canada, Air Quality Research Branch, 4905 Dufferin Street, Toronto, ON M3H 5T4 Canada
AB: Severe marine boundary layer ozone depletion episodes (ODEs) are observed every year in polar regions in the spring. Using nine years of 10-day 3D back trajectory calculations for three Arctic observatories (Alert, Barrow, and Ny Alesund), the origin of ODEs was investigated. Procedures developed by Seibert et al (1994) were used. For each observatory, 6-hourly trajectories terminating at the observatory were tagged with the ozone mole fraction that was measured at the respective arrival times. A grid system was overlaid on a map of the Arctic and each grid cell traversed by the trajectory was assigned this mole fraction. The geometric mean O3 mole fraction for the ensemble of trajectories passing over a grid cell was then calculated for the months of April, May and September. The analysis clearly shows that air passing over the Arctic Ocean in the spring had the lowest ozone mole fractions upon arrival at the three observatories. For each of the three sites, the low ozone episodes were associated with certain areas of the Arctic Ocean and with low altitude flow. On average it takes several days for an air parcel to travel from these areas to the respective measurement sites. Assuming that ozone depletion occurs over these areas, it follows that fast decreases in the ground level ozone mole fraction at a measurement site (i.e., within a few hours) is not an indication of fast chemical destruction of ozone, but rather of fast changes in the origin of the air arriving at the site. In contrast to the spring, data for the month of October indicate a much narrower mole fraction frequency distribution and no particular link between geographical area and low mole fractions of ozone.
DE: 0365 Troposphere: composition and chemistry
DE: 0368 Troposphere: constituent transport and chemistry
DE: 9315 Arctic region (0718, 4207)
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005