Changes of O3 and OH in Pearl River Delta, China in 2006-2021

Changes of O₃ and OH are important because they are the major atmospheric oxidants. Both O₃ and OH concentrations in Pearl River Delta in southern China have been increasing significantly since 2006, raising serious environmental concerns. In this study, Observation Based Methods (OBM) are developed for OH and Photochemical O₃ Production Index (PPI) to investigate the inter-annual variability and trends of  OH and O₃. We found that the overall trends of PPI, OH and O₃ in 2006-2021 could mostly be attributed to the reduction in NO2 concentrations due to emission control of NOx. However, the short-term (less than 5 years) inter-annual variations of PPI, O₃ and OH were primarily driven by meteorological processes.