Seasonal patterns, vertical profiles, and sensitivity analysis of long-term O3 pollution observations in Hefei City, China

Atmospheric pollution in China has reduced significantly due to emission reduction measures. However, major pollution incidents often occur in the Yangtze-Huaihe region. In this study, based on long-term observation of the concentrations of surface pollutants and O-3, measured using lidar, we explore the spatiotemporal variability of air pollutants in Hefei City, an important city in the Yangtze-Huaihe region, Anhui Province, China, spanning from 2015 to 2022. The results indicate that, from 2015 to 2022, the concentrations of PM2.5, PM10, O-3, NO2, SO2, and CO decreased by 58.3 %, 37.8 %, 29.1 %, 23.0 %, 59.7 %, and 12.2 %, respectively. Over the eight years, O-3 was the only pollutant that increased in concentration (from around 55.9 to 72.2 mu g.m(-3)), and the study identifies external transport as a significant contributor to the high level of O-3 pollution in the area. The generation of O-3 in Hefei City is mainly associated with the emission of volatile organic compounds (VOCs). Since 2018, China has intensified efforts to prevent and control VOCs pollution, resulting in a reduction in O-3 pollution. However, more effective control measures for VOCs are still needed in Hefei City. The analysis of O-3 production in the area revealed that O-3 pollution was dominated by local chemical generation during the daytime, with a minor amount of O-3 being transported outside the region. O-3 concentration was consumed in the area during the night through two mechanisms: transport to the other areas and surface chemical consumption. Investigating the long-term changes in O-3 and related pollutants in Hefei City enhances our understanding of the spatial and temporal characteristics of O-3 and the factors affecting O-3 pollution. Additionally, such an investigation provides a theoretical basis for the prevention and control of O-3 pollution in the Yangtze-Huaihe region.