Urban outdoor air quality

DOI: https://doi.org/10.58248/PN691 

The impacts of air pollution were highlighted by the 2013 case of Ella Adoo-Kissi-Debrah, in which high levels caused a severe fatal asthma attack. Ella is the first person in the UK to have air pollution listed as an associated cause of death following the 2020 inquest, which highlighted several organisations with responsibility for action on air pollution.  

Air quality has been the subject of infringement proceedings by the European Commission against the UK and court cases brought against the Government by the environmental law charity ClientEarth. 

The Chief Medical Officer’s 2022 Annual Report focused on air pollution, stating that “we can and should go further to reduce air pollution”.  

PM is the broad term for microscopic particles suspended in air originating from a range of human-made and natural sources. PM is classified by size range, named according to upper-limit diameter in micrometres, and comprises coarse particles (PM_10-2.5), fine particles (PM_2.5) and ultrafine particles (PM_0.1). NO₂ is one of a group of gases called nitrogen oxides (NO_x) but is the most harmful for human health. O₃ gas is not directly emitted but formed in the air. Ground level (tropospheric) O₃ can be formed by photochemical reactions (driven by sunlight) of NO_x and non-methane volatile organic compounds (NMVOCs) from various natural and human-made sources.

PM, NO₂ and O₃ have legal limit values, but low concentrations can have health impacts and no levels safe for human health have been identified. Air pollution is linked to loss of life expectancy and various acute and chronic effects that disproportionately affect certain groups. 

Across the UK, concentrations of these air pollutants are uneven.  Urban areas typically have poorer air quality, particularly deprived neighbourhoods. 

Evidence demonstrating effectiveness of measures, such as road charging schemes, encouraging less polluting transport modes and domestic combustion interventions, is limited as attributing outcomes to particular interventions is difficult due to confounding factors (such as weather conditions, seasonality and impacts of other interventions) and the health effects long-term. 

Key Points 

• Air pollution is the greatest UK environmental public health threat. It is responsible for 29,000-43,000 UK deaths annually (based on 2019 data) and multiple health effects. Between 2017 and 2025, the total estimated NHS and social care cost will be at least £1.6 billion in England.  
• Particulate matter (PM), nitrogen dioxide (NO2) and ozone (O3) are the air pollutants of most human health concern in urban areas. No safe lower limit has been identified for these pollutants, which disproportionately affect vulnerable groups. 
• In UK urban areas, average PM and NO2 concentrations are decreasing over time while O3 shows a slight increasing trend. However, some urban areas exceed the World Health Organization’s Global Air Quality guidelines for PM and NO2. 
• The Government is setting two targets for reducing PM2.5 to be met by 2040 including an annual mean concentration limit of 10 µg/m3. Modelling suggests that most of England will be compliant with this by 2030

Acknowledgements   

POSTnotes are based on literature reviews and interviews with a range of stakeholders and are externally peer reviewed. POST would like to thank interviewees and peer reviewers for kindly giving up their time during the preparation of this briefing, including:  

Members of the POST Board* 

Dr James Allan, University of Manchester and National Centre for Atmospheric Science* 

Dr Jo Barnes, University of the West of England 

Dr Suzanne Bartington, TRANSITION Clean Air Network, University of Birmingham and UKRI SPF Clean Air Champion* 

Dr Sean Beevers, Imperial College London* 

Professor William Bloss, University of Birmingham and West Midlands Air Quality Improvement Programme (WM-AIR)* 

Dr Andrew Brown, National Physical Laboratory* 

Ruth Calderwood, City of London Corporation* 

Adam Clegg, Air Quality Consultants* 

Professor Martin Clift, Swansea University and Committee on the Medical Effects of Air Pollutants* 

Dr Audrey de Nazelle, Imperial College London 

Department for Environment, Food and Rural Affairs* 

Ciaran Donaghy, Chartered Institute of Environmental Health 

Dr Karen Exley, UK Health Security Agency 

Professor Paul Fowler, University of Aberdeen* 

Dr Gary Fuller, Imperial College London and UKRI SPF Clean Air Champion* 

Alison Gowers, UK Health Security Agency* 

Professor Anna Hansell, Committee on the Medical Effects of Air Pollutants  

Professor Roy Harrison, University of Birmingham and West Midlands Air Quality Improvement Programme (WM-AIR) 

Dr James Heydon, University of Nottingham* 

Professor Sir Stephen Holgate, University of Southampton, Royal College of Physicians and UKRI SPF Clean Air Champion* 

Dr Michael Jones, Alzheimer’s Research UK* 

Dr James Levine, TRANSITION Clean Air Network, University of Birmingham* 

Dr Matthew Loxham, University of Southampton* 

Dr Hannah Macdonald, Royal Society of Chemistry  

Dr Eloise Marais, University College London* 

Imogen Martineau, Clean Air Fund 

Valentine Quinio, Centre for Cities 

Professor Stefan Reis, UK Centre for Ecology & Hydrology* 

Dr Christina Vanderwel, University of Southampton* 

*denotes people and organisations who acted as external reviewers of the briefing.