Widespread changes in UK air quality observed from space

Previous studies have used surface observations of pollutants (e.g., nitrogen dioxide [NO₂] and aerosols) to evaluate improvements in United Kingdom (UK) air quality over recent decades. However, surface monitoring networks provide limited spatial coverage and are not always representative of air quality over a wider region. Satellite observations, such as tropospheric column NO₂ (TCNO₂), aerosol optical depth (AOD) and sub‐column (0–6 km) ozone (SCO₃), provide widespread monitoring of air quality on a national scale. In this study, we use such observations to analyse trends in UK air quality, between 2005 and 2015, finding significant decreases in TCNO₂ and AOD over UK pollution hotspots. The largest changes in short‐lived NO₂ are located over populated (i.e., source) regions, associated with large emissions of nitrogen oxides (NOₓ). AOD changes are more spread out, and less strongly associated with source regions, due to a longer aerosol lifetime, secondary aerosol formation and non‐urban aerosol sources. SCO₃ shows no significant trends over England/Wales, but significant positive trends over Scotland, which is consistent with previous studies of changes in background tropospheric ozone in other remote regions of north‐western Europe.