[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].

Abstract

In recent years, ground-level-ozone（O₃） pollution in urban areas in the Bohai Rim has attracted wide attention. Based on the analysis of the spatiotemporal distribution characteristics of O₃ 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 O₃ concentration were evaluated. The results showed that： ① From 2017 to 2022, the annual assessment value of O₃ concentration in Dongying showed a fluctuating upward trend, and the pollution days with O₃ as the primary pollutant increased. O₃ pollution mainly occurred in spring, summer, and autumn, with the most severe O₃ pollution episodes typically occurring in May and June, and the duration of O₃ pollution season tended to be longer. The monthly variation in the daily maximum 8-h average ozone （MDA8 O₃） 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 O₃ concentration in recent years in Dongying also showed a significant increase trend. ② Meteorological factors greatly influenced O₃ 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 O₃ value was more likely to occur. Meteorological factors contributed 30% of the MDA8 O₃ variation in Dongying during the study period. In the case of moderate and severe O₃ pollution, the contribution of meteorological factors to the change in MDA8 O₃ could be as high as 40%. ③ To some extent, sea-land breeze contributed to the occurrence of MDA8 O₃ exceeding the secondary standard limit value of the National Ambient Air Quality Standard. In the afternoon, the hourly concentration of O₃ 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 O₃ pollution, the O₃ 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 O₃ concentration was also at a high level from 20：00 to 23：00 on sea-land breeze days. In the O₃ pollution season, the sea-land breeze could significantly affect the O₃ level in coastal cities, which could bring significant challenges for O₃ 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 O₃ 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.