Effects of heatwaves on urban air quality: Heat waves often go hand in hand with poor air quality. High temperatures and strong solar radiation increase the formation of secondary pollutants such as ozone and particulate matter. Low wind speeds and a lack of precipitation prevent pollutants from being transported away or removed from the atmosphere. Furthermore, often additional emissions from forest fires occur during heat waves. The population in cities suffers particularly from the simultaneous occurrence of heatwaves and poor air quality, as even higher temperature and lower wind speed typically prevail here and go together with higher pollutant emissions.