A study of the N2O5-SO2-O3 reaction system.

Infrared spectroscopy was used to follow the rates of the chemical changes in gaseous N(2)O(5)-SO(2) and N(2)O(5)-SO(2)-O(3) mixtures. Several results of interest to atmospheric scientists were obtained. (I) SO(3) was not a detectable product of these reaction systems, and no significant SO(2) 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: NO(3) + SO(2) leads to NO(2) + SO(3) (1); N2O5 +SO2 leads to N(2)O(4) + SO(3) (2); k(1) less than or equal to 4.2 1. mole-minus 1sec-minus 1; k(2) less than or equal to 2.5 x 10-minus 2 1. mole-minus1sec-minus 1 at 30 degrees C. These data suggest that reactions 1 and 2 are not important removal paths for SO(2) in the sunlight irradiated, NO(x)hydrocarbon polluted atmospheres. (II) The near ultraviolet absorption spectrum of pure N(2)O(5) has been determined. From these results and estimates of the actinic irradiance, it was shown that the rate of photochemical decomposition of N(2)O(5) by the absorption of solar light in the urban atmosphere is an unimportant factor among the reactions which establish the N(2)O(5) and NO(3) concentrations. (III) It has been observed that gaseous SO(3) and NO(2) 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.