Impacts of synoptic circulation on surface ozone pollution in a coastal eco-city in Southeastern China during 2014-2019

The coastal eco-city of Fuzhou in Southeastern China has experienced severe ozone (O₃) episodes at times in recent years. In this study, three typical synoptic circulations types (CTs) that influenced more than 80% of O₃ polluted days in Fuzhou during 2014-2019 were identified using a subjective approach. The characteristics of meteorological conditions linked to photochemical formation and transport of O₃ under the three CTs were summarized. Comprehensive Air Quality Model with extensions was applied to simulate O₃ episodes and to quantify O₃ sources from different regions in Fuzhou. When Fuzhou was located to the west of a high-pressure system (classified as "East-ridge"), more warm southwesterly currents flowed to Fuzhou, and the effects of cross-regional transport from Guangdong province and high local production promoted the occurrence of O₃ episodes. Under a uniform pressure field with a low-pressure system occurring to the east of Fuzhou (defined as "East-low"), stagnant weather conditions caused the strongest local production of O₃ in the atmospheric boundary layer. Controlled by high-pressure systems over the mainland (categorized as "Inland-high"), northerly airflows enhanced the contribution of cross-regional transport to O₃ in Fuzhou. The abnormal increases of the "East-ridge" and "Inland-high" were closely related to O₃ pollution in Fuzhou in April and May 2018, resulting in the annual maximum number of O₃ polluted days during recent years. Furthermore, the rising number of autumn O₃ episodes in 2017-2019 was mainly related to the "Inland-high", indicating the aggravation of cross-regional transport and highlighting the necessity of enhanced regional collaboration and efforts in combating O₃ pollution.