Heterogeneous reaction of toluene/NO2/O3 on α-Fe2O3 nanoparticles: the impacts of O3, light illumination, and relative humidity on the formation of N-containing organic compounds (NOC)

Abstract

Although the heterogeneous reactions of toluene significantly affect the atmospheric environment, less attention has been paid to the effects of O₃, light illumination, and relative humidity on the formation of N-containing organic compounds (NOC) on nanoparticles. In this study, combined effects on the heterogeneous reactions of toluene/NO₂/O₃ on α-Fe₂O₃ nanoparticles were investigated by using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results show that the addition of O₃ to the toluene/NO₂ reaction system can promote the formation processes of NOC. More toluene radicals can be formed and oxidized by the reactive oxidant species to form benzyl nitrate on the particle surface. In addition, simulated light illumination can enhance the heterogeneous conversion of toluene to NOC which may be due to the excitation effect of the photoactive properties of α-Fe₂O₃ and the intermediate product. However, increasing the relative humidity (RH) is unfavorable for NOC formation as a result of competitive effects on reactive sites and reduction of the formation of oligomers. These findings improve the understanding of combined effects on atmospheric NOC formation during the heterogeneous processes of toluene.