How a large water body modulates ozone pollution at local and regional scales: a case study of Lake Taihu and surrounding city clusters

High ozone concentrations are frequently observed over Lake Taihu despite the absence of local precursor emissions. Although previous studies have linked these events to the lake surface, the relative physical and chemical contributions remain insufficiently quantified. In this study, a severe summertime ozone episode in 2024 was investigated using the WRF-Chem model. Results showed that elevated ozone over the lake was primarily driven by strong photochemical production associated with ozone precursors transported from the upwind southern regions. The lake surface substantially suppressed planetary boundary layer (PBL) development, thereby inhibiting the upward transport of near-surface ozone while enhancing precursor accumulation and photochemical ozone production. Both processes contributed to increased ozone concentrations over the lake. In addition, lake-breeze circulation transported ozone-rich air masses toward the southern shore, further enhancing local ozone levels. During daytime, the lake increased ozone concentrations in the southern regions but decreased them in the northern regions. The areas of ozone increase and decrease reached 3285 and 3807 km2, with mean changes of +8.78 and −8.20 ppb, respectively. At night, the influence of the lake shifted toward northwestern urban areas, where ozone concentrations increased. These results highlight the important role of large water bodies in modulating ozone pollution and underscore the need to consider lake–atmosphere interactions in air quality studies over urbanized lake regions.