Source-specific ozone formation in the Pearl River Delta: Insights from direct measurement at two sites with distinct...

Ozone (O₃) precursor volatile organic compounds (VOCs) show region- and source-dependent variability. Current models often underestimate O₃ production due to incomplete reaction mechanisms, highlighting the need for direct measurement techniques to quantify the photochemical O₃. In this study, we measured net photochemical O₃ production rate (P(O₃)_net) at two sites with distinct environmental characteristics in the Pearl River Delta (PRD) region using a custom-made Net Photochemical O₃ Production Rate (NPOPR) detection system: the Guangdong Atmospheric Supersite of China in Heshan (Heshan site) and the Tianhu Atmospheric Environment Monitoring Station (Tianhu site). By using a Positive Matrix Factorization (PMF) model, we identified solvent volatilization, oil and gas volatilization, petrochemical releases, and biogenic sources at both sites, while mobile and combustion sources were only identified at the Heshan site. We then linked the O₃ formation potential (OFP) and VOC reactivity (k_OH) of different VOCs emission sources directly to the measured P(O₃)_net. Results showed that anthropogenic sources drove P(O₃)_net at Heshan site, including solvent volatilization, combustion, oil and gas volatilization, and petrochemical. In contrast, biogenic emissions drove P(O₃)_net at the Tianhu site. The results reflect the different dominant emission sources in instantaneous photochemical O₃ formation at distinct environmental sites. Further quantitative methods are needed to check the dominate contributing sources to the O₃ pollution at these two sites. It is of great significance to implement pollution source emission control measures that are tailored to local conditions for the prevention and control of O₃ pollution.