[Spatiotemporal Distribution Characteristics of Ground-level-ozone and Its Relationship with Meteorological Conditions in a Representative City in the Bohai Rim from 2017 to 2022].

In recent years, ground-level-ozone（O ₃ ） pollution in urban areas in the Bohai Rim has attracted wide attention. Based on the analysis of the spatiotemporal distribution characteristics of O ₃ concentration in Dongying, a representative city in the Bohai Rim from 2017 to 2022, the effects of meteorological factors and sea-land breeze circulation on O ₃ concentration were evaluated. The results showed that： ① From 2017 to 2022, the annual assessment value of O ₃ concentration in Dongying showed a fluctuating upward trend, and the pollution days with O ₃ as the primary pollutant increased. O ₃ pollution mainly occurred in spring, summer, and autumn, with the most severe O ₃ pollution episodes typically occurring in May and June, and the duration of O ₃ pollution season tended to be longer. The monthly variation in the daily maximum 8-h average ozone （MDA8 O ₃ ） presented a bimodal distribution, with significant increases in the 5th and 25th percentiles, and the spatial distribution was "high in the north and south, low in the middle." In addition, the nocturnal O ₃ concentration in recent years in Dongying also showed a significant increase trend. ② Meteorological factors greatly influenced O ₃ concentration in Dongying. When the temperature was greater than 30℃, the relative humidity was less than 50%, and the wind direction was south-southwest or east-northeast, a high O ₃ value was more likely to occur. Meteorological factors contributed 30% of the MDA8 O ₃ variation in Dongying during the study period. In the case of moderate and severe O ₃ pollution, the contribution of meteorological factors to the change in MDA8 O ₃ could be as high as 40%. ③ To some extent, sea-land breeze contributed to the occurrence of MDA8 O ₃ exceeding the secondary standard limit value of the National Ambient Air Quality Standard. In the afternoon, the hourly concentration of O ₃ during the sea-land breeze days was approximately 20 μg·m ^-3 higher than that during the non-sea-land breeze days. On the days of moderate and severe O ₃ pollution, the O ₃ concentration during the sea-land breeze days from 10：00 to 16：00 was higher than that during non-sea-land breeze days, and the O ₃ concentration was also at a high level from 20：00 to 23：00 on sea-land breeze days. In the O ₃ pollution season, the sea-land breeze could significantly affect the O ₃ level in coastal cities, which could bring significant challenges for O ₃ pollution prevention and control in this region. In the future, cities in the Bohai Rim need to further strengthen regional joint prevention and control of O ₃ pollution and increase emission reduction efforts of nitrogen oxides and volatile organic compounds. This strategy could effectively lower pollutant concentrations within the land breeze air mass, consequently reducing the impact of the sea breeze air mass on air quality in cities in the Bohai Rim.