Photochemical reaction characteristics and source apportionment of atmospheric volatile organic compounds during summer in Shenzhen.

Continuous online VOCs observation was carried out at urban sites in Shenzhen during the active photochemical reaction season from June to August 2022 (summer). The photochemical loss VOCs were evaluated based on the measured VOCs concentration using the photochemical age parametric method to obtain the initial VOCs concentration. The sources of initial VOCs were identified by the characteristic species ratio analysis method and Positive matrix factor model (PMF). The concentrations of photochemical consumption VOCs accounted for total VOCs (TVOCs) concentrations as follows: olefin (53.5%), oxygenated volatile organic compounds (OVOCs)(30.8%), alkane (10.9%), aromatic hydrocarbon (4.7%), acetylene (0.2%). Alkanes are dominant compounds in both initial and measured TVOCs concentration, but their photochemical loss ozone generating potential (OFP) is only 1.2×10-9, which is much lower than that of olefin (47.8×10-9), OVOCs(15.8×10-9) and aromatic hydrocarbons (4.7×10-9), suggesting that olefin is a key species for ozone pollution control. In this study, six major emission sources were obtained by PMF based on measured and initial VOCs concentrations respectively(Initial-PMF, Measured-PMF): industrial processes (0.91×10-9, 0.87×10-9), solvent use (2.75×10-9, 1.84×10-9), vehicle exhaust (3.49×10-9, 2.01×10-9), gasoline volatile (3.2×10-9, 2.62×10-9), natural source (0.74×10-9, 0.56×10-9), combustion source (2.35×10-9,1.16×10-9). It is suggested that PMF results are significantly affected by photochemical reactions, and the initial value of VOCs rather than the measured value should be considered in source apportionment, otherwise the exhaust gas and natural sources dominated by olefin will be significantly underestimated. © 2024 Chinese Society for Environmental Sciences. All rights reserved.