[Ozone Pollution in Suzhou During Early Summertime: Formation Mechanism and Interannual Variation]

This study investigated the concentrations of atmospheric pollutants in the urban area of Suzhou from May to June, 2017-2021. The variation characteristics and annual changes of ozone (O₃), nitrogen oxide (NO), total oxidant (O), carbon monoxide (CO), and volatile organic compounds (VOCs) were analyzed. The O₃ formation mechanism and its annual changes were studied using an Observation-Based Model (OBM), and VOCs source apportionments and their trends were discussed. The results indicated that ① The volume fractions of O and the concentrations of NO and CO have decreased in the urban area of Suzhou in recent years, while the volume fractions of VOCs have increased, and sufficient photochemical conditions for O₃ formation still existed during polluted days. ② The O₃-NO-VOCs sensitivity in Suzhou was in the VOCs-limited regime. The long-term reduction ratio between VOCs and NO should not be less than 5:1, and aromatics and alkenes were the critical VOCs for mitigating O₃ pollution. ③ The results of VOCs source apportionment revealed that industrial emissions, gasoline vehicle exhaust, and diesel engine exhaust were the major sources of VOC emissions in Suzhou. Industrial emissions and solvent usage declined from 2017 to 2021; however, gasoline vehicle exhaust and gasoline evaporation, which possess higher O₃ formation potential(OFP), increased significantly. ④ The OFP source apportionments results indicated that controlling VOC emissions from solvent usage and gasoline vehicle exhaust is crucial for O₃ pollution control in Suzhou.