Elucidating the molecular mechanisms of Criegee-amine chemistry in the gas phase and aqueous surface environments

Abstract

There is now an evolving body of evidence suggesting that high molecular weight oligomers from the ozonolysis of alkenes play an important role in new particle formation in the atmosphere. Using high-level quantum chemical calculations and Born Oppenheimer Molecular Dynamics (BOMD) simulations, we suggest that the reactions of anti-substituted Criegee intermediates with amine, especially dimethylamine, could lead to oligomers, which may comprise an unexplored fraction of organic nitrogen-based aerosols in urban polluted environments. The quantum chemical calculations suggest that the barrier for a given Criegee-amine reaction in the gas phase decreases with increase in methyl substitution on the amine to such an extent that the dimethylamine reactions of CH₂OO and anti-CH₃CHOO occur barrierlessly. The BOMD simulation results suggest that at the air–water interface, which represents a unique reaction medium in the atmosphere, the anti-CH₃CHOO–methylamine reaction occurs via multiple mechanisms, which are distinctly different from that in the gas phase. An important implication of these results is that the Criegee-amine chemistries may account for an appreciable fraction of aerosol particles in California's central valley, New York City and Paris areas where significant amounts of nitrogen-based aerosol particles have been detected, but their precise details are still not well understood. Alternatively, these chemistries could also serve as a potential source of the hydroxyl radical and hydrogen peroxide under tropospheric conditions.