The sensitivity analysis of a comprehensive chemical mechanism for aqueous-phase atmospheric chemistry is performed. The main aqueous-phases reaction pathways for the system are the oxidation of S(IV) by H2O2, OH, O2 (catalyzed by Fe3+ and Mn2+), O3 and HSO5. The HO2(aq) and OH(aq) radicals contribute indirectly to this process by producing and consuming H2O2(aq) H2O2(aq), respectively. The dominant pathway for HNO3(aq) acidity is scavenging of nitric acid from the gas phase. HCOOH is produced because of the reaction of HCHO(aq) with OH(aq). The gas-phase concentrations of SO2, H2O2, HO2, OH, O3, HCHO, NH3, HNO3, and HCl are of primary importance. An increase in the liquid water content of the cloud results in a decrease of the sulfate concentration but an increase of the total sulfate amount in the aqueous phase. A condensed mechanism is derived from the analysis. ¿ American Geophysical Union 1989