[Exploring Characteristics and Causes of Summer Ozone Pollution Based on Process Analysis in Wuhai]

In recent years, summer O₃ pollution has become more severe in Wuhai, where the terrain is complex and industrial parks are densely distributed. However, the characteristics and formation mechanisms of this pollution have not yet been investigated and remain unclear. Analyzing the variation and formation mechanisms of O₃ is crucial to the prevention and control of air pollution in this region. By analyzing characteristics and using a WRF-CMAQ model to simulate three O₃ pollution periods in Wuhai from June to August 2018, this study explored the causes of O₃ pollution based on in-depth process analysis, and the effects of regional transportation and local photochemical reaction on O₃ were also discussed. The diurnal variation of ozone exhibited a single-peak distribution, and near-surface O₃ was positively correlated with short-wave radiation and temperature, and negatively correlated with relative humidity. The areas of Shizuishan in Ningxia and the Ulanbuhe desert exhibited high O₃ values during the day, while the three industrial parks in Wuhai exhibited low values during both the day and night. Process analysis showed that transportation, chemical processes, and their relative magnitudes had a significant impact on O₃. Local photochemical reactions and transport during the pollution period in June and July led to an obvious increase in O₃, while the impact of chemical processes was about twice as large as that of transport. The increase of O₃ in August was mainly caused by transport. Further decomposition of the transportation effect showed that transportation in the south and northwest directions had a remarkable effects on the increase of O₃. Together with the emission of O₃ precursors, the main sources of transportation were the Yinchuan, Shizuishan, and Bayannaoer regions. Therefore, Wuhai and neighboring cities should strengthen regional joint prevention and control by jointly formulating and implementing control measures for air pollution to reduce the impact of regional transmission on O₃.