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Abstract
Infrared spectroscopy was used to follow the rates of the chemical changes in gaseous N2O5-SO2 and N2O5-SO2-O3 mixtures. Several results of interest to atmospheric scientists were obtained. (I) SO3 was not a detectable product of these reaction systems, and no significant SO2 removal occurred. From the kinetic treatment of these results, estimates were derived for the upper limits of the rate constants of the reactions 1 and 2: NO3 + SO2 → NO2 + SO3 (1); N2O5 + SO2 → N2O4 + SO3 (2); k1 = 4.2 1. mole-1sec-1; k2 ≥ 2.5 × 10-2 1. mole-1sec-1 at 30° C. These data suggest that reactions 1 and 2 are not important removal paths for SO2 in the sunlight irradiated, NOx-hydrocarbon polluted atmospheres. (II) The near ultraviolet absorption spectrum of pure N2O5 has been determined. From these results and estimates of the actinic irradiance, it was shown that the rate of photochemical decomposition of N2O5 by the absorption of solar light in the urban atmosphere is an unimportant factor among the reactions which establish the N2O5 and NO3 concentrations. (III) It has been observed that gaseous SO3 and NO2 react rapidly to form a relatively nonvolatile white solid. Preliminary data suggest a 1:1 mole ratio for this adduct. The significance, if any, of this and related compounds in urban aerosol formation must be evaluated.
