[Real-time Composition and Sources of VOCs in Summer in Wuhan]

Abstract

The hourly concentrations of 102 volatile organic compounds (VOCs) in Wuhan from June to July in 2019 were obtained using an online monitoring instrument. The ρ(VOCs) varied from 24.9 to 254 μg·m^-3, with a mean value of (67.7±32.2) μg·m^-3. According to the air quality standard of ozone, the observation period was divided into clean and polluted episodes of O₃. The differences in meteorological parameters, VOC concentrations, compositions, sources, and ozone formation potential (OFP) between clean and polluted episodes were analyzed and compared. The average mass concentrations of NO_x, CO, and VOCs in polluted periods exceeded those of clean periods by 34.9%, 25.0%, and 27.8%, respectively. The mass concentrations of alkanes, alkenes, aromatic hydrocarbons, and oxygenated volatile organic compounds in polluted periods were higher than those in clean periods by 40.7%, 39.5%, 26.9%, and 21.5%, respectively. The average OFP in polluted periods[(102±69.6) μg·m^-3] exceeded that of clean periods by 33.5%. The average contribution rates of LPG combustion, industrial sources, vehicle emissions, natural sources, and solvent usage to VOCs were 3.4%, 2.5%, 0.2%, 1.3%, and 1.4% lower than those of the clean periods, respectively, whereas the gasoline evaporation increased by 8.8% in polluted periods. The contributions of vehicle emissions and gasoline evaporation exhibited higher values in the morning and evening, with lower values in the afternoon, which may have been related to peak vehicles emissions. The contribution of LPG combustion peaked along with the cooking time. The concentration weighted trajectory showed that the main sources of VOCs in polluted periods were from local emissions and surrounding regions in the northeastern direction of Wuhan. In polluted periods, gasoline evaporation and LPG combustion should be emphasized for preventing O₃ pollution in the summer in Wuhan.

Keywords: concentration weighted trajectory(CWT); diurnal variation; ozone formation potential(OFP); real-time source apportionment; volatile organic compounds(VOCs).