Physicochemical Processes of a Typical Ozone Pollution in Suburb of Beijing

Ozone (O₃) pollution is currently a major environmental problem in some cities in China. O₃ formation depends on chemical reactions influenced by atmospheric physical processes and various meteorological conditions. Therefore, it is necessary to study near-ground O₃ pollution from both chemical and physical aspects. This study analyzed the physicochemical processes of photochemical pollution in Huairou, an urban city in Beijing, during autumn 2022. The analysis combines field observations and Eulerian photochemical box model simulations. Daily variations in meteorological factors (such as temperature, relative humidity, and wind speed) and concentrations of O₃ and its precursors including volatile organic compounds (VOCs) and nitrogen oxides (NO_x, x=1, 2) were determined. Source analysis revealed that the primary sources of VOCs are traffic emissions (46%), plant sources (25%), solvent evaporation (23%), and combustion processes (9%). The contribution of O₃ from regional transport and the reactions of local VOCs were obtained using the Euler photochemical box model. The results indicate that O₃ is primarily from horizontal transport (＞74%) during the strong north wind prevailing period. During weak south or southeast winds, O₃ is formed primarily through VOC and NO_x photochemical reactions. Based on the O₃ formation potential of VOCs, alkenes contribute the most to O₃ formation (67%), followed by aromatics (16%). Sensitivity analysis revealed that O₃ formation is most sensitive to physical factors, such as light intensity, temperature, and boundary layer height, with reactive alkenes being the most sensitive among VOCs. Finally, O₃ pollution control strategies are suggested based on the Empirical Kinetics Modeling Approach (EKMA) curves.