Quantum chemistry and computational kinetics of the reaction between OH radicals and formaldehyde adsorbed on small silica aerosol models

Abstract

Heterogeneous reactions of atmospheric volatile organic compounds (VOCs) on aerosol particles may play an important role in atmospheric chemistry. Clay particles are present in mineral dust in atmospheric aerosols, and radical reactions are thought to be heterogeneously catalyzed on them. However, the kinetics and mechanisms of adsorption and reaction of atmospheric VOCs on aerosol surfaces are not well understood. In this work, quantum chemical methods are used to study the reaction of OH radicals with formaldehyde adsorbed on small (SiO4)n cluster models, with n = 1 to 6. We show that surface adsorbed formaldehyde can react in the presence of gas-phase OH radicals to yield surface-bound formyl radicals and water. Significant exothermic adsorption energies are found, supporting the notion that silicate surfaces are good quenchers of VOCs. With the models employed, the reaction appears to be less favored on the silicate surfaces than in the gas phase. The effect of the model surface on the reaction mechanism is analyzed.