Investigation of the summer 2018 European ozone air pollution episodes using novel satellite data and modelling

In the summer of 2018, Europe experienced an intense heatwave which coincided with several persistent large-scale ozone (inline-formulaO₃) pollution episodes. Novel satellite data of lower-tropospheric column inline-formulaO₃ from the Global Ozone Monitoring Experiment-2 (GOME-2) and Infrared Atmospheric Sounding Interferometer (IASI) on the MetOp satellite showed substantial enhancements in 2018 relative to other years since 2012. Surface observations also showed ozone enhancements across large regions of continental Europe in summer 2018 compared to 2017. Enhancements to surface temperature and the inline-formulaO₃ precursor gases carbon monoxide and methanol in 2018 were co-retrieved from MetOp observations by the same scheme. This analysis was supported by the TOMCAT chemistry transport model (CTM) to investigate processes driving the observed inline-formulaO₃ enhancements. Through several targeted sensitivity experiments we show that meteorological processes, and emissions to a secondary order, were important for controlling the elevated inline-formulaO₃ concentrations at the surface. However, mid-tropospheric (inline-formula∼ 500 inline-formulahPa) inline-formulaO₃ enhancements were dominated by meteorological processes. We find that contributions from stratospheric inline-formulaO₃ intrusions ranged between 15 %–40 %. Analysis of back trajectories indicates that the import of inline-formulaO₃-enriched air masses into Europe originated over the North Atlantic, substantially increasing inline-formulaO₃ in the 500 inline-formulahPa layer during summer 2018.