Synergistic Reaction of SO(2) with NO(2) in Presence of H(2)O and NH(3): A Potential Source of Sulfate Aerosol

Effect of H(2)O and NH(3) on the synergistic oxidation reaction of SO(2) and NO(2) is investigated by theoretical calculation using the molecule system SO(2)-2NO(2)-nH(2)O (n = 0, 1, 2, 3) and SO(2)-2NO(2)-nH(2)O-mNH(3) (n = 0, 1, 2; m = 1, 2). Calculated results show that SO(2) is oxidized to SO(3) by N(2)O(4) intermediate. The additional H(2)O in the systems can reduce the energy barrier of oxidation step. The increasing number of H(2)O molecules in the systems enhances the effect and promotes the production of HONO. When the proportion of H(2)O to NH(3) is 1:1, with NH(3) included in the system, the energy barrier is lower than two pure H(2)O molecules in the oxidation step. The present study indicates that the H(2)O and NH(3) have thermodynamic effects on promoting the oxidation reaction of SO(2) and NO(2), and NH(3) has a more significant role in stabilizing product complexes. In these hydrolysis reactions, nethermost barrier energy (0.29 kcal/mol) can be found in the system SO(2)-2NO(2)-H(2)O. It is obvious that the production of HONO is energetically favorable. A new reaction mechanism about SO(2) oxidation in the atmosphere is proposed, which can provide guidance for the further study of aerosol surface reactions.