Impact of lake-atmosphere exchange on summertime ozone in the Lake Taihu region

Abstract

Local circulation generated by thermal differences between a lake and the surrounding land impacts dispersion and chemical transformation of ozone, whereas it is challenging to resolve these processes in models. In this study, we use the WRF-Chem model coupled with the modified CLM4.5 lake model to reproduce the local circulation and ozone concentrations during a high-temperature and high-ozone-concentration event in the Lake Taihu (TH) region, and we explore how lake–atmosphere exchange affects ozone pollution. We find that the variations of ozone concentrations around Lake Taihu is regulated by lake breezes and the thermal inner boundary layer (TIBL). Due to the formation of the TIBL, ozone concentrations in the lakeshore area within 5 km from TH are significantly higher than those in other areas by approximately 20 ppb. Lake–atmosphere exchange positively contributes to the ozone pollution event for about 35 ppb at approximately noon, due to the accumulation of ozone and its precursors in the lake area caused by the land breeze at night and the favorable conditions for the photochemical reaction of ozone on the lake surface during the day. This research produces theoretical innovations on the frontier issues related to the interactions of shallow lake–atmosphere–ozone pollution and provides a new understanding of the interactions among the three.