Formation processes of nitrogen-containing organic compounds from heterogeneous reactions of C3H6/NO2/O3 with α-Fe2O3 particles

Formation processes of nitrogen-containing organic compounds (NOCs) are important from heterogeneous reactions between volatile organic compounds (VOCs) and mineral oxides under various environmental factors. In this study, reaction processes of C 3 H 6 /O 3 /NO 2 with α-Fe 2 O 3 particles were studied by using a gas-flow system with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results show that the appearance of R–ONO 2 bands at ∼1648 and 1286 cm −1 represents the formation of NOCs. In the dark condition, the presence of O 3 leads to the rapid formation of nitrate radical (NO 3 ) which can react with C 3 H 6 to form NOCs on particle surface. Under the simulated sunlight irradiation, the α-Fe 2 O 3 can be excited to produce additional hydroxyl which promotes the formation of RO 2 . Meanwhile, formed NO from the photolysis of NO 2 can react with RO 2 to produce more NOCs. Moreover, the presence of water vapor plays a negative role in the NOCs formation processes. The value of uptake coefficient for the NO 2 in the initial stage at 0% relative humidity (RH) is about 10 times higher than that at 76.3% RH during the heterogeneous reactions. The R–ONO 2 group hydrolyzes to nitric acid and R–OH under the humid condition. Our results lay the foundation on the effects of light irradiation and RH for the converting VOCs into NOCs on mineral dust and help to understand the formation processes of NOCs under combined atmospheric environment.