Heterogeneous and multiphase chemistry of trace atmospheric gases with mineral dust and other metal containing particles

Abstract

In this study, we investigated the effect of relative humidity on the oxidation of cyclohexane by photogenerated •OH radicals on TiO2 surface. At zero relative humidity (RH), only surface adsorbed oxidation products are present. In the presence of gas phase water vapor at higher relative humidities, gas phase cyclohexanone was also detected as an oxidation product. This gas phase cyclohexanone concentration was increased with increasing RH until 40%. This gas phase cyclohexanone product is absent at 73% RH. There are two possible sources of gas phase cyclohexanone; a) reaction of •OH radicals diffused into the gas phase with cyclohexane molecules b) diffusion of cyclohexanone molecules formed on the TiO2 surface to the gas phase. Absence of any gas phase products at 73% RH is probably due to limitations in the diffusion of •OH radicals or cyclohexanone product formed on the surface to the gas phase due to thicker adsorbed water layer.