Characteristics and Formation Mechanism of Surface Ozone in a Coastal Island of Southeast China: Influence of Sea-land Breezes and Regional Transport

The ozone (O_3) concentrations in island cities are low due to the relatively low concentrations of O_3 precursors. However, Pingtan, a typical island city along the southeast coast of China, suffers from frequent O_3 pollution. In this study, one year of hourly O_3 concentration data collected from three sites (rural, suburban, and urban) on Pingtan were used to investigate the characteristics and formation mechanism of O_3 pollution. The results showed that the minimum O_3 concentrations measured at the three sites were larger than 55.53 μg m^(-3), which was likely caused by low NO titration over Pingtan. The O_3 concentrations in summer were low because of the East Asian monsoon. The daily maximum O_3 concentrations with sea and land breezes (SLBs) were higher than those without SLBs at all three sites (8.52, 9.84, and 14.30 μg m^(-3) at the rural, suburban, and urban sites, respectively). In addition, SLBs amplified the diurnal variation in O_3 concentrations. Cluster analysis and the analysis of an episode of high O_3 concentration indicated that the developed Yangtze River Delta is the main source of O_3 in Pingtan. This study helps reveal the characteristics and formation mechanism of O_3 pollution in island cities.