Effects of Heatwaves on European Ground Level Ozone Pollution in Recent Years

Heatwaves are phenomena that are occurring with increasing frequency, a trend which is expected to continue over the coming century as the effects of climate change continue to be felt, as has been well documented in the IPCC’s AR6 synthesis report. Heatwaves are of direct concern to human health due to exposure to extreme heat, but also for their secondary impacts including those on air pollution.  A heatwave describes a period of hot weather where the air temperature exceeds a climatological average for that region, for example the UK’s Met Office defines these based on the average temperature in a region for the 15th July 1991 - 2020. The meteorology surrounding heatwaves is usually characterised by stagnant conditions, allowing air pollutants to remain closer to their sources and allowing secondary pollutants to form there. Tropospheric ozone is one of these air pollutants, created through the reactions of nitrogen oxides and volatile organic compounds and is harmful to human health. As a part of the World Meteorological Organisation’s Air Quality and Climate Bulletin (2023), we included a short report on the effects of the July 2022 heatwave on ozone concentrations measured across several hundred air quality monitoring stations which were located primarily in urban and rural background locations in Europe. Here we present an extended analysis examining heatwave events over the last decade and their contribution to the number of extreme ozone events experienced at these sites.