Abstract/Summary

The impact of poor air quality (AQ) on public health has long been recognised and considerable efforts have been made to improve it across the UK. The UK has a far reaching AQ monitoring network and this study summarises the evolution of UK AQ over the period 2015–2024, focusing on the pollutants NO 2 , O 3 and PM 2 . 5 and exploring their drivers. Concentrations of NO 2 and PM 2 . 5 exhibit robust negative trends across the whole country while concentrations of O 3 increase. Comparing 2015–2016 to 2023–2024, the median number of days per year for which DEFRA AQ sites breached the WHO 2021 target decreased from 136 to 40 (−70%) for NO 2 and from 60 to 22 (−63%) for PM 2 . 5 . This trend was mirrored in other AQ monitoring networks and highlights that, while progress is being made, acceptable levels of AQ are yet to be reached. Over the same period, median O 3 exceedances increased from 7 to 14 days per year. Nationwide analysis of diurnal variation in the pollutants and the use of airmass back trajectory clustering and statistical modelling for three locations – Reading, Sheffield and Glasgow – suggests that local traffic plays a dominant role in NO 2 pollution, PM 2 . 5 is influenced more by long range transport and O 3 increases are being driven in part by decreases in NO 2 . From an AQ policy perspective, this suggests continued focus on traffic emissions will reduce NO 2 , (inter)national rather than local efforts are most critical for PM 2 . 5 improvements, and reductions to VOC emissions must accompany NO 2 if further O 3 increases are to be avoided.