Introduction Ambient air quality is, in essence, the quality of the air outdoors. The World Health Organization (WHO) explains that: ‘Ambient (outdoor) air pollution in both cities and rural areas was estimated to cause 4.2 million premature deaths worldwide per year in 2019; this mortality is due to exposure to fine particulate matter, which causes cardiovascular and respiratory disease, and cancers.’ House of Commons Research Briefing: Air quality: policies, proposals and concerns (HC Library, March 2025) stated that poor air quality is considered by the government to be ‘the largest environmental risk to public health in the UK’. It added that as well as human health, ‘… air pollution also has implications for the natural environment and for the economy. Due to the transboundary nature of air pollution, action to manage and improve air quality in the UK has been driven by both international agreements and EU legislation, as well as national and devolved legislation’. The report went on set out its cause for concern and that: ‘It is widely acknowledged that air pollution has a significant public health