Pollutionwatch: How harmful ozone builds up near ground in heatwaves

Medics attend to an incident in Liege, Belgium, during last month’s hot weather. Ozone levels were raised during the heatwave. Photograph: Olivier Matthys/EPA

Widespread air pollution was a feature of June’s record-breaking heat across western Europe and is likely to increase again as the UK experiences its third heatwave of the summer.

UK weather warnings for extreme heat from 22 June were followed by a rare high air pollution alert from the London mayor.