UK air quality showed clear improvement from 2015 to 2024 but breaching of targets remains very common†

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 NO₂, O₃ and PM_2.5 and exploring their drivers. Concentrations of NO₂ and PM_2.5 exhibit robust negative trends across the whole country while concentrations of O₃ 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 NO₂ 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 O₃ 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 NO₂ pollution, PM_2.5 is influenced more by long range transport and O₃ increases are being driven in part by decreases in NO₂. From an AQ policy perspective, this suggests continued focus on traffic emissions will reduce NO₂, (inter)national rather than local efforts are most critical for PM_2.5 improvements, and reductions to VOC emissions must accompany NO₂ if further O₃ increases are to be avoided.