OXIDATION OF AQUEOUS SULFITE ION BY NITROGEN-DIOXIDE

The reaction of nitrogen dioxide with aqueous sulfite solutions, in the presence and in the absence of oxygen, has been studied using Raman spectroscopy to determine product concentrations. The products observed include nitrite, sulfate, and dithionate ions. The reaction appears to initially produce nitrite ion and sulfite radical: NO2 + SO32- --> NO2- + SO3.-. The sulfite radical can undergo either recombination or reaction with oxygen to form SO5.-. In the absence of oxygen, we obtain a ratio of [SO42-]/[S2O62-] = 1.8 +/- 0.3, reflecting the branching of the recombination of sulfite radical: SO3.- + SO3.- --> S2O62- or SO3.- + SO3.- --> SO32- + SO3. The production Of SO3.- and SO5.- radicals from the nitrogen dioxide-sulfite ion reaction suggests that this reaction could contribute significantly to S(IV) oxidation in atmospheric aerosols under suitable conditions.