Call for Evidence - Future PM2.5 concentrations in England

News published: 19/11/2020


The Environment Bill, currently passing through parliament requires government to set legally binding environmental targets for England in four priority areas including air quality. In the policy paper published by Defra on 19th August 2020 ( the government indicated its intention to set two air quality targets relating to fine particulate matter (PM2.5), as this is the air pollutant of greatest harm to human health. It is proposed that one target will be based on annual mean concentration of PM2.5 as stated in clause 2 of the Environment Bill, and the other would be on population exposure reduction. The development of these targets will be informed by evidence and analysis, including input from independent experts.


The Air Quality Expert Group (AQEG), together with the Committee on the Medical Effects of Air Pollutants (COMEAP), are providing independent technical advice to Defra throughout the development of the air quality targets. At the request of Defra, AQEG are seeking input from the wider research community on future PM2.5 concentrations in England via a Call for Evidence. This information will be used to provide context and interpretation of model runs conducted specifically to inform target setting.

AQEG will undertake a review of all evidence received and produce a summary synthesis which will form part of the supporting evidence which will accompany the public consultation on air quality targets. That report, and all contributions received will be published on the UK-AIR website, and all materials fully credited to their originators.

Based on the brief survey questions below, respondents may be invited to provide more information and/or present their evidence to Defra / AQEG, and participate in a virtual discussion regarding model projections of future PM2.5. [A limited amount of funding may be available from Defra to recompense the time spent preparing for, and participating in these discussions, if this is required. Any funding provided will be awarded at the discretion of Defra].

Please send your responses to the AQEG Secretariat at by 17th December 2020.

Feel free to append any additional documents that may be of relevance such as peer-reviewed papers or reports to support your responses. You do not need to respond to all the questions. At this stage we are looking for short summary responses to the questions of not more than around two pages. As described above we may contact you to ask if you are willing to provide more information and/or be willing to present further information to support further Defra and AQEG discussions.

Key questions

1. What evidence can you provide that would be informative of how the annual average PM2.5 concentration in England might change in future years?

We are seeking information obtained from either ambient air quality modelling covering all or part of England, projecting PM2.5 concentrations which include dates between the present day and 2040, or wider evidence derived from changes in relationships between emissions trends/activities and ambient concentrations.

Information and insight into the likely future composition of PM2.5 in England would be very valuable, including estimates of primary PM, secondary inorganic and secondary organic aerosols. Information on a range of spatial scales is likely to be valuable, as will insight into future PM2.5 and the associated composition in both the urban and rural environments.

Please provide a short description of your technical approach (or include a relevant publication) providing details of the model used, model set-up, the scenarios run, assumptions made and the input data and data/reference source. If you have carried out any comparison with monitoring or other models that could indicate the validity of your findings, please provide details of these.

2. What evidence could you provide on the main sources for PM2.5 and the factors which drive changes in concentrations of PM2.5 and how these might change in the future?

Please provide an outline of any modelling or other information which is available to you which identifies the main sources and drivers for change with regards to PM2.5 concentrations in England and how these might change in the future. Of interest are results from air quality modelling that quantify how the proportion of primary and secondary PM might change in the future, and the modelling of the contribution of specific sources of PM2.5 e.g. sectors such as domestic combustion or non-exhaust emissions from road vehicles, or non-anthropogenic and transboundary PM. Results from modelling the impact of particular interventions or policies such as net zero and future trends such as increased home working would also be valuable.

3. What are the main uncertainties in determining future PM2.5 concentrations?

Please identify any evidence you may have relating to sensitivity studies using air quality models or analysis of source data which could help to identify the main areas of uncertainty in modelling future PM2.5 concentrations. This could include modelling uncertainties/assumptions, gaps in emissions data or meteorological or other external influences.

4. What evidence do you have on how population exposure might change in the future?

Please identify if you have evidence relating to population exposure to PM2.5 and how this might change in the future, for example due to changes in emissions, population growth, increased urbanisation or behaviour. Please provide any additional details on exposure to PM2.5 for vulnerable groups such as children and people with respiratory illnesses; or where PM2.5 exposure leads to inequalities in health outcomes on the basis of income, deprivation or ethnicity.

Statement from Defra:
Defra would ask the research community to support the UK government in its efforts to reduce air pollution through the development of air quality targets. Evidence and insight into possible changes to future PM2.5 concentration will help us to develop ambitious and effective targets which drive action to improve air quality.
John Newington, Head of Evidence, Air Quality and Industrial Emissions, Defra

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