Why Heat Makes Ozone Worse in Cities but Not the Countryside

A study published in Atmospheric Chemistry and Physics examines why ozone gets worse during heatwaves in cities, using the Yangtze River Delta’s summer 2022 as a case. Led by Chang Su of the University of Edinburgh with collaborators from Reading and Edinburgh, the research combines ground-level measurements with chemistry-model experiments. Comparing Shanghai with Lishui, a forested area in southwestern Zhejiang where over 80% of land is wooded and nitrogen oxide levels are low, the authors find ozone rises with temperature at both locations, but about twice as fast in the city. In Shanghai, ozone increases 7.27 micrograms per cubic meter per °C, versus 3.36 in Lishui. Humidity further drives the effect, since drier air reduces ozone destruction by water vapor.