Abstract A Community Multiscale Air Quality model with the Master Chemical Mechanism is applied to evaluate the reactions of stabilized Criegee Intermediates SCIs with SO 2 (k SCI+ SO 2) on sulfate aerosols in the eastern United States (US) during the summer of 2006. Surface sulfate concentrations and total sulfate columns increased by as much as 18% and 6%, respectively, when (k SCI+ SO 2) was increased from 7× 10− 14 cm 3 s− 1 to a suggested value of 3.9× 10− 11 cm 3 s− 1. The episode-average increase of the top-of-atmosphere direct radiative forcing due to the additional sulfate can be as much as− 0.7 W m− 2 (5%). However, if the SCI+ H 2 O reaction rate constant (k SCI+ H 2 O) was also increased based on the reported ratio of k SCI+ H2O to (k SCI+ SO 2)(6.1× 10− 5), the surface sulfate and total sulfate column increases were less than 0.5%, which suggests that the impact of SCIs on sulfate may be insignificant and additional studies are needed to better determine k SCI+ H 2 O. Small SCIs such as CH 2 OO and CH 3 CHOO, and SCIs from isoprene (MVKOO) and monoterpene (APINBOO) oxidation are the dominant SCIs in the eastern US.