[Ambient VOCs Characteristics and Reactivity During O₃ Pollution in Autumn in Urban Beijing]

In order to understand the effect of volatile organic compounds (VOCs) on ozone pollution, the concentrations, chemical composition variations, and ozone formation potential (OFP) were studied under different O₃ concentrations, using high-resolution online monitoring data obtained in the urban site of Beijing in autumn of 2019. The results showed that the average concentration of VOCs was (22.22±10.10)×10^-9, with the largest contribution of VOCs from alkanes (55.65%), followed by that of oxygenated volatile organic compounds (OVOCs) (16.23%) and alkenes (8.13%). Three ozone pollution episodes were captured during the observation period. The average concentration of VOCs on pollution days was (26.22±12.52)×10^-9, which was 60.17%higher than that on clear days (16.37±7.19)×10^-9. The value of ozone formation potential (OFP) on pollution days was 113.63 μg·m^-3, which was 56.55%higher than that on clear days. The contributions of OVOCs and aromatics to OFP on pollution days increased by 6.51%and 1.55%, respectively, whereas that of alkenes declined (8.72%). The ratios of toluene to benzene (T/B) and benzene, toluene, and ethylbenzene (B:T:E) were 1.55 and 0.36:0.55:0.09, respectively, indicating that vehicle exhaust had significant effects on VOCs in autumn in urban Beijing. The back-trajectory results indicated a high contribution of southern air masses to atmospheric VOCs variations in autumn in urban Beijing.