Characterizations of ozone and related compounds under the influence of maritime and continental winds at a coastal site in the Yangtze Delta, nearby Shanghai

In this study, some distinct characteristics of surface ozone and related compound (NO, NO2, and CO) levels during maritime winds (MW) and continental winds (CW) at a coastal site in the Yangtze Delta, nearby Shanghai, were presented and discussed. The frequency of MW was higher in spring and summer and lower in autumn and winter. The ozone level during MW was much higher than those during CW in each season, while the primary pollutant levels presented the opposite result. There may be ozone depression processes during CW at the site caused by relatively fresh primary pollutants, which are transported from urban Shanghai. In contrast, pollutants during MW were more aged, so the ozone depression processes were weak and the ozone level was high. Due to the lack of fresh NO, the daily ozone maximum was lagged, and the early morning ozone minimum was obscured during MW. Ozone concentrations during CW presented evident “weekend effect”, while the concentrations during MW showed obvious anti-“weekend effect”. Just like in urban Shanghai, “weekend effect” during CW in the site is mainly associated with “VOCs-limited” and the change of NO2/NO ratio. The ozone anti-“weekend effect” during MW might be associated with the high NOx concentrations in weekend, which were caused by the recirculation of the pollutants carried over in weekdays from urban areas during CW.