[Analysis of a Typical Ozone Pollution Process in Guangzhou in Winter]

This study focused on an ozone pollution event occurring in winter (January) in Guangzhou. Various influencing factors were analyzed, including various atmospheric trace gases, meteorological conditions during the whole pollution process, as well as the characteristics of the main O₃ precursor volatile organic compounds (VOCs). The main sources of VOCs and the O₃ formation regime were analyzed using an array of tools:the ozone potential formation (OFP), positive matrix factorization (PMF) model, and empirical kinetic modeling approach (EKMA) curve. Feasible strategies for O₃ control were suggested. The results showed that O₃ and NO₂ exceeded the corresponding standards in this winter pollution event, when the concentrations of PM₁₀ and PM_2.5 were also high, differing from the air pollution characteristics in summer and autumn. Low boundary layer height (<75 m) and high atmospheric stability at night exacerbated the accumulation of ozone precursors and fine particles. Meteorological conditions such as the increased daytime temperature (5℃), stronger solar radiation (10%), and low horizontal wind speed (<1 m·s^-1) favored photochemical reactions and promoted the formation of ozone and fine particles. VOCs were mainly composed of alkanes, and the proportions of alkanes and alkynes in winter were higher than those in the other seasons. Aromatics (xylenes and toluene) and propylene were the key VOCs species leading to O₃ formation. The main VOCs sources were vehicle exhaust (22.4%), solvent usage (20.5%), and industrial emissions (17.9%); however, the source with highest OFP was identified as solvent usage. O₃ formation in this event was in the VOCs-limited regime, and reducing O₃ precursors in the VOCs/NO ratio of 3:1 was effective and feasible for O₃ control. This study explored the causes of an O₃ pollution event in winter, which will serve as reference for the synergistic control of O₃ and PM_2.5 in heavy pollution seasons.