Air pollution across the UK has shown significant improvement between 2015 and 2024, according to recent research published in Environmental Science: Atmospheres by the University of Reading. Despite reductions in key pollutants such as nitrogen dioxide (NO2) and fine particulate matter (PM2.5), the country continues to breach air quality targets, especially for surface ozone (O3).

Researchers analysed air pollution levels at over 500 monitoring sites across the UK, focusing on three major pollutants known to affect human health. The findings show that NO2 levels, primarily from traffic emissions, decreased by an average of 35% across these sites. PM2.5 levels, which refer to fine particles capable of penetrating deep into the lungs, dropped by 30% on average.

While these figures reflect positive trends, pollution limits are still exceeded too often. The number of days per year that NO2 levels went above the World Health Organization (WHO) recommended limits fell from an annual average of 136 days to 40 days. PM2.5 exceedances also reduced, from 60 to 22 days annually.

In contrast, surface ozone pollution has worsened. The data reveals a 17% average increase in O3 levels over the same period. The number of days when ozone levels exceeded WHO thresholds doubled from 7 to 14 days per year. Surface ozone is produced through chemical reactions between NO2 and volatile organic compounds (VOCs), under sunlight. This makes it more complex to manage, particularly as efforts to cut NO2 alone can unintentionally lead to rising O3 levels unless VOCs are simultaneously controlled.

The research also emphasises that different pollution types originate from various sources and thus require tailored responses. NO2 is largely local, mainly from road transport. PM2.5, on the other hand, can travel long distances, entering the UK from other regions and countries, particularly continental Europe. This long-range movement makes PM2.5 more challenging to control solely through local efforts. Ozone pollution, due to its dependence on chemical reactions involving other gases and sunlight, often results from both local and international emissions.

The findings underscore the importance of adopting a multi-pollutant approach to air quality management. For NO2, strategies such as promoting cleaner vehicles and public transport can help reduce local concentrations. PM2.5 levels require broader cooperation across national borders, with a need for stricter industrial and agricultural emissions controls across Europe. Managing ozone requires coordinated reductions of both NO2 and VOC emissions, especially in urban areas, to avoid worsening the problem as other pollutants decline.

The research indicates that a narrow focus on reducing a single pollutant may not result in overall air quality improvements. Instead, policies need to be designed to address the full range of pollutants in an integrated way, accounting for their complex interactions. Measures must also be adaptable to different geographic areas, depending on the dominant sources of pollution in each location.

Despite notable progress in reducing traffic-related pollution, the ongoing breach of health-based targets across the UK reflects that the country is still falling short of its clean air goals. It also points to the critical need for international collaboration, especially in tackling pollutants like PM2.5 and ozone that transcend national boundaries.

The full study, titled UK air quality showed clear improvement from 2015 to 2024 but breaching of targets remains very common, was published in Environmental Science: Atmospheres (2025), DOI: 10.1039/d5ea00055f.

Source & Credits:
Provided by University of Reading. Published in Environmental Science: Atmospheres (2025). DOI: 10.1039/d5ea00055f