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. With the rapid advance in urbanization, land use and anthropogenicheat (AH) dictated by human activities significantly modify the urbanclimate and in turn the air quality. Focusing on the Yangtze River Delta(YRD) region, a highly urbanized coastal area with severe ozone (O3)pollution, we estimate the impacts of land use and AH on meteorology andO3 using the Weather Research and Forecasting model coupled to Chemistry (WRF-Chem). These results enhance our understanding ofthe formation of O3 pollution in rapidly developing city clusters withplace-specific topography, as most of our results can be supported byprevious studies conducted in other regions around the world. RegionalO3 pollution episodes occurred frequently (∼ 26 times peryear) in the YRD from 2015 to 2019. These O3 pollution episodes areusually in calm conditions characterized by high temperature (over 20 ∘C), low relative humidity (less than 80 %), light wind (less than3 m s−1) and shallow cloud cover (less than 5 okta). In this case,O3 pollution belts tend to appear in the converging airflows associatedwith the sea and the lake breezes. On the other hand, rapid urbanization hassignificantly changed land use and AH in this region, which subsequentlyaffects meteorology and O3 concentration. The largest change inland use comes from urban expansion, which causes an increase in 2 mtemperature (T2) by a maximum of 3 ∘C, an increase in planetaryboundary layer height (PBLH) by a maximum of 500 m, a decrease in 10 m windspeed (WS10) by a maximum of 1.5 m s−1 and an increase in surfaceO3 by a maximum of 20 µg m−3. With regard to the sea andlake breezes, the expansion of coastal cities, like Shanghai, can enhancethe sea breeze circulation by ∼ 1 m s−1. During theadvance of the sea breeze front inland, the updraft induced by the frontcauses strong vertical mixing of O3. However, once the sea breeze isfully developed in the afternoon (∼ 17:00 LT), furtherprogression inland will stall. Then O3 removal by the low sea breezewill be weakened, and surface O3 can be 10 µg m−3 higher inthe case with cities than in the case with no cities. The expansion of lakeside cities, suchas Wuxi and Suzhou, can extend the lifetime of lake breezes from noon toafternoon. Since the offshore flow of the lake breeze transports highO3 from the land to the lake, the onshore flow brings high O3 backto the land. Surface O3 in lakeside cities can increase by as much as 30 µg m−3. Compared to land use, the effects of AH are relativelysmall. The changes mainly appear in and around cities where AH fluxes arelarge. There are increases in T2, PBLH, WS10 and surface O3when AH fluxes are taken into account, with increments of approximately 0.2 ∘C, 75 m, 0.3 m s−1 and 4 µg m−3, respectively. AHcontributes largely to the urban environment, altering meteorologicalfactors, O3 concentration and urban breeze circulation, but its effecton the sea and the lake breezes seems to be limited.

Land use and anthropogenic heat modulate ozone by meteorology: a perspective from the Yangtze River Delta region