Role of Atmospheric VOCs in Ozone Formation in Summer in Shanghai Suburb

Abstract

In order to study the role of VOCs in the formation of ozone during the high ozone season in summer in Shanghai, 103 volatile organic compounds, ozone, and nitrogen oxides were measured at state ecology and environment scientific observation and research station for the Yangtze River Delta at Dianeshan Lake from May to August 2018. The average volume fraction of VOCs was 32.7×10-9 during the high ozone season in Shanghai. Carbonyl compounds were the main components of VOCs, accounting for 35.0%. Among the carbonyl compounds, the volume fraction of formaldehyde was the highest, followed by acetone, accounting for 82.8% of the total carbonyl compounds. The chemical reaction activity of ambient air was the strongest in May, and the total ozone formation potential (OFP) was 337.2 μg·m-3. Formaldehyde had the highest contribution. The examination of the diurnal variations in alkanes, alkenes, and aromatics revealed higher average concentrations at nighttime than at daytime, with a small peak in the morning, which was related to the impact of traffic emissions. Aldehydes and ketones varied diurnally by having higher average concentrations during the daytime than those at nighttime, which was related to the secondary formation process of photochemical reactions. The observation-based model (OBM) showed that O3 formation was in a VOC-limited regime from May to June and in a transition regime from July to August.