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

Abstract

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.