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Published June 1987 | public
Journal Article

Transport and oxidation of SO_2 in a stagnant foggy valley


The fate of SO_2 emitted in the San Joaquin Valley of California under stagnant foggy conditions was determined by the release of an inert tracer and the concurrent monitoring of SO_2 and SO_4^(2−) concentrations. At night, SO_2 was found to be trapped in a dense fog layer below a strong and persistent inversion based a few hundred meters above the valley floor. This lack of ventilation led to the accumulation of SO_2 and SO_4^(2−) over a major SO_2 source region in the valley. The rate of oxidation of SO_2 to SO_4^(2−) in fog was estimated at 3 ± 2%h^(−1). Production of acidity from the oxidation of SO_2 fully titrated the NH_3(g) present before the fog, and led to a progressive drop of the fogwater pH over the course of the night. In the afternoon, the valley was found to be efficiently ventilated by a buoyant upslope flow through the inversion. The tracer data indicated that about 40 % of the air transported upslope in the afternoon was returned to the valley in the night-time drainage flow. The fates of SO_2 and SO_4^(2−) in the valley during extended high-inversion episodes appear to depend considerably on the presence of fog or stratus, and on the extent of daytime insolation.

Additional Information

© 1987 Elsevier. First received 27 June 1986 and in final form 31 October 1986. We thank D. Gudgel and the Bakersfield National Weather Service office for providing us with the Oildale sampling site and accurate weather forecasts. We also thank D. Anderson from the Bakersfield Texaco office for her helpful co-operation. This research was funded by the California Air Resources Board, Contract No. A4-075-32.

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