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METHODS FOR SIMULATING GAS PHASE SO2 OXIDATION IN ATMOSPHERIC MODELS
Citation:
Meagher, J. AND K. Olszyna. METHODS FOR SIMULATING GAS PHASE SO2 OXIDATION IN ATMOSPHERIC MODELS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/3-85/012.
Description:
Two different approaches are presented for simulating gas phase sulfur dioxide oxidation in atmospheric models. The first approach was to develop an empirical relationship based on rate data collected at four coal-fired power plants during 11 separate studies. Cosine functions were used to simulate annual and diurnal variations in the oxidation rate constant. The second approach was to develop a kinetic model based on data obtained from smog chamber experiments using mixtures of sulfur dioxide, propene, butane, nitrogen oxides, and water vapor. Sulfur dioxide oxidation in the gas phase was found to occur by two mechanisms. At low HC/NOx values hydroxyl radical addition to sulfur dioxide predominates. At high HC/NOx values, oxidation via reaction with products of the ozone-olefin reaction dominates. The chamber data suggest that the HO-SO2 reaction leads mainly to the production of hydroperoxyl radical and sulfuric acid. A previously proposed mechanism for the reaction of sulfur dioxide with Criegee intermediates was found to provide an excellent fit to the data at the high HC/NOx values.