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

Abstract

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 C3H6/O3/NO2 with α-Fe2O3 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–ONO2 bands at ∼1648 and 1286 cm−1 represents the formation of NOCs. In the dark condition, the presence of O3 leads to the rapid formation of nitrate radical (NO3) which can react with C3H6 to form NOCs on particle surface. Under the simulated sunlight irradiation, the α-Fe2O3 can be excited to produce additional hydroxyl which promotes the formation of RO2. Meanwhile, formed NO from the photolysis of NO2 can react with RO2 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 NO2 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–ONO2 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.