OXIDATION OF AQUEOUS SULFITE ION BY NITROGEN-DIOXIDE

The reaction of nitrogen dioxide with aqueous sulfite solutions, in th e presence and in the absence of oxygen, has been studied using Raman spectroscopy to determine product concentrations. The products observe d 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 obtai n a ratio of [SO42-]/[S2O62-] = 1.8 +/- 0.3, reflecting the branching of the recombination of sulfite radical: SO3.- + SO3.- --> S2O62- or S O3.- + SO3.- --> SO32- + SO3. The production Of SO3.- and SO5.- radica ls from the nitrogen dioxide-sulfite ion reaction suggests that this r eaction could contribute significantly to S(IV) oxidation in atmospher ic aerosols under suitable conditions.