Ozone and fine particle in the western Yangtze River Delta: an overview of 1 yr data at the SORPES station

This work presents an overview of 1 yr measurements of ozone (O-3) and fine particular matter (PM2.5) and related trace gases at a recently developed regional background site, the Station for Observing Regional Processes of the Earth System (SORPES), in the western part of the Yangtze River Delta (YRD) in eastern China. Ozone and PM2.5 showed strong seasonal cycles but with contrast patterns: O-3 reached a maximum in warm seasons but PM2.5 in cold seasons. Correlation analysis suggests a VOC-sensitive regime for O-3 chemistry and a formation of secondary aerosols under conditions of high O-3 in summer. Compared with the National Ambient Air Quality Standards in China, our measurements report 15 days of O-3 exceedance and 148 days of PM2.5 exceedance during the 1 yr period, suggesting a severe air pollution situation in this region. Case studies for typical O-3 and PM2.5 episodes demonstrated that these episodes were generally associated with an air mass transport pathway over the mid-YRD, i.e., along the Nanjing-Shanghai axis with its city clusters, and showed that synoptic weather played an important role in air pollution, especially for O-3. Agricultural burning activities caused high PM2.5 and O-3 pollution during harvest seasons, especially in June. A calculation of potential source contributions based on Lagrangian dispersion simulations suggests that emissions from the YRD contributed to over 70% of the O-3 precursor CO, with a majority from the mid-YRD. North-YRD and the North China Plain are the main contributors to PM2.5 pollution in this region. This work shows an important environmental impact from industrialization and urbanization in the YRD region, and suggests an urgent need for improving air quality in these areas through collaborative control measures among different administrative regions.