How Photochemically Consumed Volatile Organic Compounds Affect Ozone Formation: A Case Study in Chengdu, China

Abstract

Surface ozone (O3) pollution has not improved significantly in recent years. It is still the primary air pollution problem in many megacities in China during summertime. In high temperature and intense radiation weather, volatile organic compounds (VOCs) are easily oxidized and degraded to induce O3 pollution. In order to understand the impact of difference between photochemical initial concentration (PIC) of VOCs and the actual measured concentration on O3 formation, a campaign was carried out during O3 pollution in Chengdu (25 July–5 August 2021). During this O3 pollution episode, the maximum value of O3 concentration reached 335.0 μg/m3, and the precursor concentrations increased significantly. The mean values of VOCmeasured and VOCPICs were 19.7 ppbv and 30.7 ppbv, corresponding to O3 formation potential (OFP) of 175.3 μg/m3 and 478.8 μg/m3, respectively, indicating that the consumption of VOCs content could not be ignored. Alkenes accounted for 77.2% of VOCs consumption. Alkenes and aromatics contributed 63.0% and 29.2% to OFP values which derived from PIC of each VOC species. The relative incremental reactivity analysis based on PICs showed that the O3 formation was controlled by the cooperation of nitrogen oxides (NOx) and VOCs, and the effect of NOx emission reduction was better.

Keywords

• ozone pollution
• volatile organic compounds
• photochemical initial concentration
• ozone sensitivity
• Chengdu