THE OXIDATION RATE AND RESIDENCE TIME OF SULPHUR DIOXIDE IN THE ARCTIC ATMOSPHERE

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Abstract

The Arctic air mass contains gaseous and particulate compounds that originate mainly from fossil fuel combustion at mid-latitudes and especially from the Eurasian sector. Observations of the temporal variation of SO2, SO2−4 and V concentrations in the North American and Norwegian Arctic are presented. At Igloolik, Canada, 3–7-day average SO2 concentrations ranged from 2.3 to 4.3 μg m−3 in February to much lower values in spring and fall. The most probable cause of similar strong variations in the ratio of SO2−4 to V observed throughout the North American Arctic is a seasonally varying SO2 oxidation rate. Interpreted in the light of a Lagrangian transport model, observations indicate that the mean SO2-oxidation rate between Eurasian sources and the North American Arctic is 0.1% h−1 in early December, 0.04% h−1 in late February, and 0.1–0.2% h−1 in early April. The residence time of SO2, controlled not only by chemical conversion to sulphate but also by dry deposition, is 14–20 days in late fall, 16–32 days at mid-winter and 10–19 days in April. The estimated rates of SO2 oxidation cannot be explained by photochemical oxidation mechanisms at least when reactive hydrocarbons are ignored.

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