Research and analysis

Particulate matter as PM2.5 compliance assessment 2025

Published 9 October 2026

This compliance assessment is part of Air pollution in the UK 2025. There is a page for each of 12 pollutants.

This page provides the UK’s compliance assessment for 2025 against the limit value and the national exposure reduction target (NERT) set for particulate matter less than 2.5 micrometres in diameter (PM2.5).

The compliance criteria is set in the Air Quality Standards Regulations (2010).

The Air Quality Standards Regulations (2010) require reporting of compliance on an annual basis. This report continues the series of annual compliance reporting .

More stringent targets have been set in England for PM2.5 since the Air Quality Standards Regulations (2010). Progress towards additional PM2.5 targets in England, is published in a separate Accredited Official Statistics publication.

1. PM2.5 pollution and its impacts

Particulate matter (PM) is a mixture of solid particles and liquid droplets suspended in air. It effectively includes everything in the air that is not a gas and therefore consists of a huge variety of chemical compounds and materials, some of which can be toxic.

Particulates are classified according to size. The UK regulates the fractions of PM where particles are less than 10 micrometres in diameter (PM10) and less than 2.5 micrometres in diameter (PM2.5), which is based on evidence on the effects of PM to health.

Due to the small size of many of the particles that form PM, these particles may enter the bloodstream and be transported around the body, lodging in the heart, brain and other organs.

Therefore, exposure to PM can result in serious impacts on health, especially in vulnerable groups of people such as the young, elderly, and those with respiratory problems. 

The UK has been compliant with the PM2.5 limit value for over a decade. Nonetheless, public health benefits would be expected from further reductions, given that the available evidence has not identified a threshold below which no adverse health effects occur.

Progress towards additional PM2.5 targets in England, is published in a separate Accredited Official Statistics publication.

2. Sources of PM2.5 pollution

The release of pollutants into the atmosphere is known as emissions.  Annual UK emissions of PM2.5 are estimated each year and are presented in Defra’s Accredited Official Statistics publication, Emissions of Air Pollutants. The latest estimates currently available are for 2024.

The National Atmospheric Emissions Inventory reports emissions of PM2.5 from human activities in the UK, but there are a few exceptions included as memo items, such as international shipping and aviation. The information presented here does not include memo items.

PM2.5 can be ‘primary’ (emitted directly to the atmosphere) or ‘secondary’ (formed by the chemical reaction of other pollutants in the air). The National Atmospheric Emissions Inventory only estimates primary emissions.

The national total of PM2.5 emissions across the UK decreased by 75 per cent from 1990 to 2024.  

Emissions of PM2.5 originate from a wide range of activity sources, with no single activity dominating. In 2024, emissions from households burning wood indoors were greater than the emissions from industrial combustion. Emissions of PM2.5 from road transport include tailpipe emissions, but the majority comes from tyre and brake wear, and road abrasion.

Quarrying and construction activities emit PM in the larger size fractions, and are therefore significant sources of PM10 emissions, but not PM2.5 emissions.

PM2.5 typically remains in the atmosphere for a longer time than gases (such as nitrogen dioxide) and can therefore be transported further from the location it was first emitted. A proportion of the concentrations of PM2.5 that we experience in the UK comes from transboundary sources, such as continental Europe. Previously deposited PM2.5 can also be resuspended by activities such as road transport.

3. Trends in PM2.5 pollution

PM2.5 pollution has generally improved; average annual mean concentrations of PM2.5 measured at urban background sites has reduced from 12.4 µg/m3 in 2009 to 8.0 µg/m3 in 2025.

A similar decline is also reported for urban traffic monitoring locations across the same period. Annual average concentrations fell in 2020 and have remained below 2019 levels ever since.

The annual air quality statistics published for particulate matter provide further information on trends in the pollutant as measured by the Automatic Urban and Rural Network (AURN) as well as reporting progress against the Environment Act Targets (Fine Particulate Matter) (England) Regulations (2023).

4. Spatial variation in PM2.5 across the UK in 2025

Concentrations of PM2.5 tend to be greatest in urban environments, and in the southern and eastern areas of the UK due to a variety of factors, including:

• higher population density
• weather conditions
• greater exposure to pollution sources from mainland Europe

Figure 1 shows modelled annual mean PM2.5 concentrations for 2025 for each 1x1km grid square of the UK. The data comes from the CMAQ-Urban Model, used for supplementary assessment against the PM2.5 limit value set for the protection of health, as set out in section 6. The modelled distribution of PM2.5 in 2025 shows the typical pattern of higher concentrations in the south-east of the UK, and lower concentrations in the north-west.

Figure 1: Modelled annual mean PM2.5 concentrations for 2025

Note that Figure 1 shows the modelled annual average background concentration of PM2.5 in each 1x1 km grid square of the UK. Within the grid squares, there may be local areas of higher concentration close to specific emission sources, such as busy roads or in areas of increase solid fuel burning.  These will not be visible in the background maps.

5. Episodes of PM2.5 pollution in 2025

This section looks at short term episodes of moderate, or above, PM2.5 pollution in the UK. Air pollution is communicated on the Daily Air Quality Index (DAQI), a simple scale that explains the short-term health risk of air pollution in words, numbers and colours.

See the guidance on pollutant concentrations for the DAQI.

Figure 2 is a calendar view of the DAQI for PM2.5 concentrations in 2025. Each day in the year is represented by a coloured square. The majority of squares are coloured green, denoting that all AURN monitoring sites recorded PM2.5 concentrations that fell within the ‘low’ pollution band on most days. However, there were also 24 days which recorded ‘moderate’ PM2.5 concentrations, one day which recorded ‘high’ PM2.5 concentrations and 2 days which recorded ‘very high’ PM2.5 concentrations. The ‘high’ concentration occurred on 3 December 2025, and the ‘very high’ concentrations occurred on 10 March and 7 April 2025. The month of March exhibited widespread concentrations at ‘moderate’ concentrations or above.

Figure 2: Calendar plot of the DAQI for PM2.5 at AURN monitoring sites in 2025

Note 1: The colour of each square represents the maximum DAQI across the national network. The number shown in each square is the total number of stations which recorded a ‘moderate’ concentration or above.

Figure 3 presents the daily mean PM2.5 concentration at all AURN monitoring sites in March and April.  Figure 3 shows how PM2.5 concentrations across most AURN sites tended to vary in a similar way. For example, on 10 March 2025 it is clear that elevated PM2.5 concentrations were measured across most AURN monitoring sites. This is most likely due to the weather conditions during this period; the Met Office note that March was characterised by extensive high pressure, which would have resulted in less dispersion and may have brought pollutants from mainland Europe. There were also numerous reports of wildfires across the UK in March, which may have contributed to elevated PM2.5 concentrations.

The ‘very high’ concentration recorded on 7 April 2025 was isolated to just a single AURN site just outside Glasgow (Greenock A8 Roadside) but was not picked up at nearby AURN sites within Glasgow. The Scottish Fire and Rescue Service issued a bulletin on 7 April 2025 noting that there were numerous wildfires that were being dealt with during this period but did not explicitly identify a fire within close proximity of the Greenock A8 Roadside site.

The ‘high’ concentration recorded on 3 December 2025 was isolated to a single site in Bradford, which was not seen in the concentrations recorded at the nearby AURN sites in Leeds. This site also recorded elevated PM10 concentrations at the start of December.

Figure 3: Daily mean PM2.5 concentration at AURN monitoring sites in March and April 2025

Note 1: Each separate light blue line denotes the daily mean concentration at AURN sites where PM2.5 is measured. Dotted horizontal lines indicate the minimum respective concentrations for the ‘moderate’, ‘high’, and ‘very high’ DAQI bands.

6. PM2.5 limit value and national exposure reduction target

Table 1 outlines the limit value and the national exposure reduction target (NERT) set for PM2.5 concentrations.

Compliance against the PM2.5 limit value is assessed within each zone of the UK. For further information on agglomeration and non-agglomeration zones see the methods for 2025 Air Quality Standards Regulations (2010) compliance assessment.

Under the Air Quality Standards Regulations (2010), the UK was required to achieve the NERT for PM2.5 over the period 2010 to 2020. The UK achieved the NERT in 2016, well before the 2020 target year, but has continued to report compliance annually, even after 2020, to demonstrate that it remains compliant.

Compliance is assessed on the basis of the average exposure indicator (AEI) statistic. The AEI for the UK is calculated as follows:

1. Each year, the annual arithmetic mean PM2.5 concentration is calculated for the designated AEI subset of urban background sites. A consistent subset of sites is used to allow for year to year comparability.
2. The mean of the most recent 3 calendar years’ values is taken as the AEI.

The detailed methodology and results of this calculation are presented in Defra’s technical report on UK air quality assessment.

The AEI for the reference year (2010) was 13 µg/m3. Based on this, the Air Quality Standards Regulations (2010) set an exposure reduction target of 15%, which equated to reducing the AEI to 11 µg/m3 by 2020.

Table 1: PM2.5 compliance criteria

Description	Averaging period	Metric
PM2.5 limit value	Annual mean	20 µg/m3
PM2.5 NERT	Average exposure indicator (AEI)	% reduction in AEI between baseline (2010) and target year (2020)

The rules for assessing compliance are set out in the Air Quality Standards Regulations (2010), as amended.

New targets for PM2.5

More stringent targets have been set in England for PM2.5 since the Air Quality Standards Regulations (2010).

The Environment Act 2021 established a new framework for environmental targets for England. The Environmental Targets (fine particulate matter) (England) Regulations (2023) set targets under this framework for the air pollutant most harmful to health – fine particulate matter (PM2.5).

The 2 targets to be met by 2040 are:

• annual mean concentrations of PM2.5 to be 10 µg m-3 or lower
• population exposure to PM2.5 to be reduced by at least 35 per cent compared to 2018 levels

The 2 targets are designed to work together to drive actions that both reduce concentrations where they are highest and reduce the pollution that everyone in the country experiences.

Interim targets for 2030 were published in the Environmental Improvement Plan 2025.

See the Accredited Official Statistics for more information on these targets and the progress made so far.

7. Evidence used for assessing compliance

See the methods for 2025 Air Quality Standards Regulations (2010) compliance assessment.

The evidence base for the annual assessment of compliance against the PM2.5 limit value is underpinned by a combination of measurements and the results of modelling assessments. The use of models enables air quality to be assessed at locations without monitoring sites. It has the added benefit of providing additional information on source apportionment and projections to support the development and implementation of air quality policies.

For further information on the measurements and the models used in the 2025 compliance assessment, and to download the data, see air quality compliance assessment 2025: results and data tables.

Monitoring

In 2025, there were 130 monitoring stations from the AURN network which met the data quality requirements for assessment against the PM2.5 limit value. This includes:

• 65 background stations
• 40 roadside monitoring stations
• 7 industrial monitoring stations
• 18 rural background monitoring stations

Modelling

The CMAQ-Urban Model was used for compliance assessment in 2025.

For assessment against the PM2.5 limit value, 2 model outputs were calculated:

• annual average PM2.5 concentrations for each 1x1km grid square of the UK
• annual average concentrations of PM2.5 at the roadside, 4m from the kerb, for each major urban road of the UK

For more information on the modelling methods and for access to the data, see the air quality compliance assessment 2025: modelled data and reports.

Modelled data is also made available in accessible formats within air quality compliance assessment 2025: results and data tables. 

8. Compliance assessment for 2025

All zones were compliant with the limit value for annual mean PM2.5 concentrations in 2025.

The 3-year running mean AEI for 2025 (calculated as the mean of designated urban background monitoring sites, rounded to the nearest integer), is 7 µg/m3. Therefore, the UK remained compliant with the NERT in 2025.

The results of the assessment are also made available within the air quality compliance assessment 2025: results and data tables.

To see progress towards PM2.5 targets in England, see the Accredited Official Statistics for PM2.5 targets (PERT and AMCT).

9. Changes in compliance over time

This section provides information on non-compliances in previous years from 2008 onwards. 2008 is the year that limit values for pollutants were set in the EU Air Quality Directive, which was subsequently transposed into UK legislation by the Air Quality Standards Regulations (2010).

The UK has been compliant with the limit value set for PM2.5 since 2008.