Characteristics of volatile organic compounds, NO2, and effects on ozone formation at a site with high ozone level in Chengdu

Chengdu is a megacity in the southwest of China with high ozone (O-3) mixing ratio. Observation of volatile organic compounds (VOCs), NO2 and O-3 with high temporal resolution was conducted in Chengdu to investigate the chemical processes and causes of high O-3 levels. The hourly mixing ratios of VOCs, NO2, and O-3 were monitored by an online system from 28 August to 7 October, 2016. According to meteorological conditions, Chengdu, with relative warm weather and low wind speed, is favorable to O-3 formation. Part of the O-3 in Chengdu may be transported from the downtown area. In O-3 episodes, the average mixing ratios of NO2 and O-3 were 20.20 ppbv and 47.95 ppbv, respectively. In non-O-3 episodes, the average mixing ratios of NO2 and O-3 were 16.38 ppbv and 35.15 ppbv, respectively. The average mixing ratio of total VOCs (TVOCs) was 40.29 ppbv in non-O-3 episodes, which was lower than that in O-3 episodes (53.19 ppbv). Alkenes comprised 51.7% of the total O-3 formation potential (OFP) in Chengdu, followed by aromatics which accounted for 24.2%. Ethylene, trans-pentene, propene, and BTEX (benzene, ethylbenzene, toluene, m/p-xylene, o-xylene) were also major contributors to the OFP in Chengdu. In O-3 episodes, intensive secondary formations were observed during the campaign. Oxygenated VOCs (OVOCs), such as acetone, Methylethylketone (MEK), and Methylvinylketone (MVK) were abundant. Isoprene rapidly converted to MVK and Methacrolein (MACR) during O-3 episodes. Acetone was mainly the oxidant of C3-C5 hydrocarbons. (c) 2018 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B. V.