Analysis of chemical kinetics at the gas-aqueous interface for submicron aerosols

Abstract

The effect of kinetics of chemical reactions in the gas–liquid interface between atmospheric gases and reactive solute in dilute aqueous aerosols is analysed in order to see if such processes will affect the overall uptake rate. Accordingly, a parameterization of such heterogeneous reactions was derived, taking into account interfacial reactions. Gibbs surface excess concentration of both reactive compounds and stable compounds leads to higher heterogeneous reaction rates in comparison to aqueous phase bulk reactions. An analytical formulation shows that the surface reactions may be of considerable importance for the uptake process in the case of small liquid aerosols even in the absence of organic film on the surface. In particular, we demonstrate that the uptake rate of atmospheric gas-phase oxidants (such as OH, NO₃ or O₃) reacting with volatile organic compounds (such as ethanol or methanol) is increased by more than 10% for atmospheric aerosols with diameters lower than 0.1 μm. This effect is in addition intensified in the case of reactions of atmospheric oxidants with liquid aerosols containing organic surfactants, such as semi-volatile organic compounds, i.e., the chemical reactions at the gas–liquid interface may be dominant in the main uptake process for atmospheric submicron aerosols.