The hydrolysis of NO2 dimer in small clusters of sulfuric acid: A potential source of nitrous acid in troposphere

Abstract

Hydrolysis of NO2 dimer is of great interest in atmospheric chemistry because it can form HONO, a major source of OH in polluted urban atmospheres. Herein, the reaction mechanism and kinetics for the hydrolysis of trans-ONONO2 (the favorable route in the hydrolysis of NO2 dimer) catalyzed by catalyst X (X = H2SO4, H2SO4⋯H2O, and (H2SO4)2) have been studied theoretically. The calculated results show that the addition of X not only increases the stabilization energy of the reactant complex, but also decreases the energy barrier by over 7.0 kcal⋅mol−1. Kinetic simulations show that H2SO4⋯H2O exerts the strongest catalytic role as compared with H2SO4, and (H2SO4)2 with its pseudo-first-order rate constant kt′(SW) respectively larger by 6–5 and 10–11 orders of magnitude. Additionally, compared with the rate constant of t-ONONO2 + H2O reaction, the kt′(SW) of t-ONONO2 + H2SO4···(H2O)2 reaction increase by 13 times at 298 K. Therefore, the present work may suggest that formation of nitrous acid from the hydrolysis reaction of t-N2O4 is promoted significantly by pre-existing aerosols of small clusters of sulfuric acid.