Photochemical Reaction of NO2 on Photoactive Mineral Dust: Mechanism and Irradiation Intensity Dependence

Abstract Photochemical reaction of NO2 on semiconductor is of scientific significance in both photocatalytic NOx removal and nitrogenous aerosol formation. A fundamental understanding of the reaction mechanism and how irradiation intensity influences the product distribution and reaction kinetics remains uncertain. By means of DRIFTS (diffuse reflection infrared Fourier transform spectroscopy) and flow reactor system, we for the first time investigated the irradiation-intensity-dependence of this heterogeneous process. Surface nitrate and nitrite present opposite variations in response to light intensity. The formation rate of individual nitrogenous product is susceptible to the intensity variation of weak irradiation, while tends to be unsusceptible under strong irradiation. The phenomenon is explained by the balance between heterogeneous uptake of NO2 and photoinduced generation of reactive oxygen species varying with irradiation intensity. The highest yield of total nitrogenous products appears under weak irradiation, indicating the photolysis of nitrite and photoreduction of nitrate under strong irradiation. The experimental results suggest that irradiation intensity should be introduced into atmospheric models for its varied impacts on heterogeneous chemistry. Moreover, irradiation intensity should be considered as an important factor in the photocatalytic removal of NOx.