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The hydrolysis of CH 2 OO is not only a dominant sink for the CH 2 OO intermediate in the atmosphere but also a key process in the formation of aerosols. Herein, the reaction mechanism and kinetics for the hydrolysis of CH 2 OO catalyzed by the precursors of atmospheric aerosols, including H 2 SO 4 , H 2 SO 4 ···H 2 O, and (H 2 SO 4 ) 2 , have been studied theoretically at the CCSD(T)-F12a/cc-pVDZ-F12//B3LYP/6-311+G(2 df ,2 pd ) level. The calculated results show that the three catalysts decrease the energy barrier by over 10.3 kcal·mol -1 ; at the same time, the product formation of HOCH 2 OOH is more strongly bonded to the three catalysts than to the reactants CH 2 OO and H 2 O, revealing that small clusters of sulfuric acid promote the hydrolysis of CH 2 OO both kinetically and thermodynamically. Kinetic simulations show that the H 2 SO 4 -assisted reaction is more favorable than the H 2 SO 4 ···H 2 O- (the pseudo-first-order rate constant being 27.9-11.5 times larger) and (H 2 SO 4 ) 2 - (between 2.8 × 10 4 and 3.4 × 10 5 times larger) catalyzed reactions. Additionally, due to relatively lower concentration of H 2 SO 4 , the hydrolysis of CH 2 OO with H 2 SO 4 cannot compete with the CH 2 OO + H 2 O or (H 2 O) 2 reaction within the temperature range of 280-320 K, since its pseudo-first-order rate ratio is smaller by 4-7 or 6-8 orders of magnitude, respectively. However, the present results provide a good example of how small clusters of sulfuric acid catalyze the hydrolysis of an important atmospheric species.

The H 2 O 2 + HO → HO 2 + H 2 O reaction is an important reservoir for both radicals of HO and HO 2 catalyzing the destruction of O 3 . Here, this reaction assisted by NH 3 and HCOOH catalysts was explored using the CCSD(T)-F12a/cc-pVDZ-F12//M06-2X/aug-cc-pVTZ method and canonical variational transition state theory with small curvature tunneling. Two possible sets of mechanisms, (i) one-step routes and (ii) stepwise processes, are possible. Our results show that in the presence of both NH 3 and HCOOH catalysts under relevant atmospheric temperature, mechanism (i) is favored both energetically and kinetically than the corresponding mechanism (ii). At 298 K, the relative rate for mechanism (i) in the presence of NH 3 (10, 2900 ppbv) and HCOOH (10 ppbv) is respectively 3-5 and 2-4 orders of magnitude lower than that of the water-catalyzed reaction. This is due to a comparatively lower concentration of NH 3 and HCOOH than H 2 O which indicates the positive water effect under atmospheric conditions. Although NH 3 and HCOOH catalysts play a negligible role in the reservoir for both radicals of HO and HO 2 catalyzing the destruction of O 3 , the current study provides a comprehensive example of how acidic and basic catalysts assisted the gas-phase reactions., Competing Interests: The authors declare no competing financial interest., (This journal is © The Royal Society of Chemistry.)