National statistics

Particulate matter (PM10/PM2.5)

Updated 27 April 2023

National Statistics

Air quality statistics in the UK, 1987 to 2022 - Particulate matter (PM10/PM2.5)

Updated 27 April 2023

1. Why measure PM?

Particulate matter (PM) is 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. Due to the small size of many of the particles that form PM some of these toxins 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 to health, especially in vulnerable groups of people such as the young, elderly, and those with respiratory problems. As a result, particulates are classified according to size. The UK is currently focused on measuring the fractions of PM where particles are less than 10 micrometres in diameter (PM10) and less than 2.5 micrometres in diameter (PM2.5) based on the latest evidence on the effects of PM to health.

Both PM and the precursor pollutants that can form it can travel large distances in the atmosphere. A small proportion of the concentrations of PM that people in the UK are exposed to come from naturally occurring sources such as pollen and sea spray (approximately 15 per cent). Another third is transported to the UK from other European countries. However, around half of UK concentrations of PM comes from anthropogenic sources in the UK such as domestic wood burning and tyre and brake wear from vehicles. As such, it is in the interest of the UK to measure concentrations of PM as close to these sources of anthropogenic emissions as possible in order to effectively assess exposure to PM that can be tackled via UK policies.

The Air Quality Standards Regulations 2010 require that concentrations of PM in the UK must not exceed:

  • An annual average of 40 µg/m3 for PM10;

  • A 24-hour average of 50 µg/m3 more than 35 times in a single year for PM10;

  • An annual average of 20 µg/m3 for PM2.5.

The Environmental Targets (Fine Particulate Matter) (England) Regulations 2023 require that in England by the end of 2040:

  • An annual average of 10 µg/m3 for PM2.5 is not exceeded at any monitoring station.
  • Population exposure to PM2.5 is at least 35% less than in 2018.

Population exposure refers to the average concentration someone in England is exposed to and is based on urban or in some case suburban background measurements which are representative of the type of environment most people live and work. 

The Environmental Improvement Plan 2023 for England set interim targets that by January 2028:

  • An annual average of 12 µg/m3 for PM2.5 is not exceeded at any monitoring station.
  • Population exposure to PM2.5 is at least 22% less than in 2018.

2.1 Annual mean concentrations of PM10 in the UK, 1992 to 2022

The PM10 index shows the annual mean, averaged over all included sites that had annual data capture greater than or equal to 75%. The shaded areas represent the 95% confidence interval for the annual mean concentration for roadside sites and urban background sites. These intervals narrow over time because of an increase in the number of monitoring sites for both roadside and urban background sites; and a reduction in the variation between annual means for PM10 measured at roadside sites. Annual means for individual sites can be found in the PM10 statistical tables that accompany this report.

Figure 5: Annual mean concentrations of PM10 in the UK, 1992 to 2022

Figure 5: Annual mean concentrations of PM10 in the UK, 1992 to 2022

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Urban background PM10 pollution has reduced in the long-term despite a period of relative stability between 2017 and 2022.

There has been an overall decrease in annual mean concentrations of PM10 at urban background sites from 36.1 µg/m3 in 1992 to 13.9 µg/m3 in 2022.

Between 1992 and 2000 inclusive, the annual mean PM10 concentration at urban background sites reduced rapidly: by an average of 1.7 µg/m3 each year. This reduction was observed at most monitoring sites across the UK and could be a consequence of the large reduction in emissions of PM10 over the same period in the UK.

Between 2000 and 2006 the annual mean concentration fluctuated with no clear trend, and this was observed at most monitoring sites across the UK. Emissions of PM10 in the UK and Europe were still decreasing over this period but the reductions were largely driven by changes to fuels used for energy generation which may have a minimal impact on urban air quality.

Between 2006 and 2015 inclusive, the annual mean PM10 concentration at urban background sites reduced gradually by an average of 1.0 µg/m3 each year. Concentrations were stable from 2015 to 2019 until a notable decrease between 2019 and 2020 of 1.8 µg/m3 (12%). There was further slight decrease (2%) to 13.0 µg/m3 in 2021, the lowest value in the time series. From there, concentrations have risen slightly to 13.9 µg/m3 in 2022.

Roadside PM10 pollution has reduced in the long-term.

Annual average concentrations of PM10 at the roadside steadily declined from 36.7 µg/m3 in 1997 to 17.2 µg/m3 in 2015. Between 1997 and 2015 inclusive, the annual mean PM10 concentration at roadside sites gradually decreased by an average of 1.1 µg/m3 each year. This reduction was observed at most long-running monitoring sites across the UK. This reduction could be a consequence of the large reduction in emissions of PM10 over the same period in the UK, particularly from road transport sources.

Concentrations of PM10 at the roadside have remained relatively stable between 2015 and 2022. PM10 concentrations were slightly lower in 2020, and in 2021 concentrations of PM10 dropped to the lowest value in the time series (15.9 µg/m3). Concentrations in 2022 have increased to 16.9 µg/m3.

The annual mean PM10 concentration in 2022 is greater at roadside sites compared to urban background sites. This is most likely due to the contribution of PM10 emissions from road transport sources, predominantly from non-exhaust sources (brakes, tyres and road wear), as well as the impact of resuspension due to vehicle movements.

3.1 Annual mean concentrations of PM2.5 in the UK, 2009 to 2022

The PM2.5 index shows the annual mean, averaged over all included sites that had annual data capture greater than or equal to 75%. The shaded areas represent the 95% confidence interval for the annual mean concentration for roadside sites and urban background sites. The interval for roadside sites narrows over time because of an increase in the number of monitoring sites and a reduction in the variation between annual means for PM2.5 measured at roadside sites. Annual means for individual sites can be found in the PM2.5 statistical tables that accompany this report.

Figure 6: Annual concentrations of PM2.5 in the UK, 2009 to 2022

Figure 6: Annual concentrations of PM2.5 in the UK, 2009 to 2022

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Urban background PM2.5 pollution has generally decreased despite a period of little change between 2015 and 2019

In general, annual average concentrations of PM2.5 at urban background sites have decreased from 12.4 µg/m3 in 2009 to 8.3 µg/m3 in 2022. The decline in concentrations of PM2.5 at urban background sites approximately follows the trends seen for PM10 at urban background sites (PM2.5 is a subset of PM10).

Concentrations increased between 2009 and 2011, when a downward trend began towards 2015 followed by a period of relatively stability through to 2019. Concentrations then were lower in 2020 and have remained relatively stable since. In 2022, mean concentrations rose slightly (by 5%) from 2021 levels.

Roadside PM2.5 pollution has generally decreased despite a period of little change between 2015 and 2019.

In general, annual mean concentrations of PM2.5 at the roadside have decreased from 12.8 µg/m3 in 2009 to 8.7 µg/m3 in 2022, rising by 0.7 µg/m3 since the lowest point in the time series in 2020. The decline in concentrations of PM2.5 at roadside sites approximately follows the trends seen for PM10 at roadside sites (PM2.5 is a subset of PM10).

There were 3 roadside monitoring sites in 2022 which recorded an annual mean greater than the maximum mean captured by any urban background monitoring site.

Concentrations of PM2.5 tend to be greatest in urban environments in the southern and eastern areas of the UK due to a variety of factors, including higher population density, weather conditions and greater exposure to pollution sources from mainland Europe. In 2022 all of the top 5 sites in urban environments (4 roadside and 1 background) with the greatest annual mean concentration of PM2.5 were located in the South or East (including London).

4. Average hours spent in ‘Moderate’ or higher PM pollution

This metric measures the annual trend in the number of hours per monitoring site that concentrations are recorded at levels that may have impacts on human health. For example, ‘Moderate’ air pollution (which requires action by citizens who are vulnerable to the health impacts of air pollution) for PM10 is triggered when the latest 24-hour running mean concentration is greater than 50 µg/m3. The coloured categories relate to the categories of the Daily Air Quality Index (see Table 20 in the statistical tables that accompany this release).

Figure 7: Annual mean hours when PM10 pollution was ‘Moderate’ or higher, for roadside sites, 1997 to 2022

Figure 7: Annual mean hours when PM10 pollution was ‘Moderate’ or higher, for roadside sites, 1997 to 2022

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Figure 8: Annual mean hours per site when PM10 pollution was ‘Moderate’ or higher, for urban background sites, 1992 to 2022

Figure 8: Annual mean hours per site when PM10 pollution was ‘Moderate’ or higher, for urban background sites, 1992 to 2022

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Roadside and urban background monitoring sites have recorded fewer hours of ‘Moderate’ or higher PM10 air pollution in the long term

At roadside and urban background sites the long-term trend has been a decline in the number of hours for which the mean PM10 concentration over the previous 24 hours exceeded 50 µg/m3.

At the roadside the mean number of hours where PM10 concentrations exceeded this ‘Moderate’ threshold for a monitoring site decreased by 93% between 1997 and 2022 to 94 hours; an average decrease of 49 hours per year over the period.

At urban background sites the mean number of hours where PM10 concentrations exceeded the ‘Moderate’ threshold for a monitoring site decreased by 95% between 1992 and 2022 to 62 hours; an average decrease of 35 hours per year per site over the period.

The downward trend in the time series has been interrupted in several years; most notably in 2003. In March and April 2003, meteorological analysis showed that concentrations at many monitoring sites were elevated due to primary emissions from Northern or Central Europe along with secondary particles caused by chemical reactions in the atmosphere. When cleaner Atlantic airflows became dominant in April 2003, pollution levels dropped considerably - see Air Pollution in the UK, 2003.

More recently, the downward trend was interrupted in 2019, but to a lesser degree. Meteorological analysis indicated that two UK-wide particulate pollution episodes occurred in February and April of 2019. Both of these events primarily resulted from a combination of warm, sunny weather causing increased local and foreign particulate suspension along with light, easterly winds transporting a substantial amount of particulate matter from Europe. It is probable that these events contributed to the relatively high number of hours of PM10 pollution observed in 2019 - see Air Pollution in the UK, 2019.

For PM2.5, ‘Moderate’ air pollution (which requires action by citizens who are vulnerable to the health impacts of air pollution) is triggered when the latest 24-hour running mean concentration is greater than 35 µg/m3. The coloured categories relate to the categories of the Daily Air Quality Index (see Table 20 in the statistical tables that accompany this release).

Figure 9: Annual mean hours when PM2.5 pollution was ‘Moderate’ or higher for roadside sites, 2009 to 2022

Figure 9: Annual mean hours when PM2.5 pollution was ‘Moderate’ or higher for roadside sites, 2009 to 2022

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Figure 10: Annual mean hours when PM2.5 pollution was ‘Moderate’ or higher for urban background sites, 2009 to 2022

Figure 10: Annual mean hours when PM2.5 pollution was ‘Moderate’ or higher for urban background sites, 2009 to 2022

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Overall, roadside and urban background monitoring sites have recorded a decreasing trend in hours of ‘Moderate’ or higher PM2.5 air pollution since 2011.

At roadside and urban background sites there has been a downward trend in the number of hours for which the mean PM2.5 concentration over the previous 24 hours exceeded 35 µg/m3 since 2011.

At the roadside the mean number of hours where PM2.5 concentrations exceeded this ‘Moderate’ threshold for a monitoring site decreased by 89% between the peak year 2011 to 64 per site in 2022.

At urban background sites the mean number of hours where PM2.5 concentrations exceeded the ‘Moderate’ threshold for a monitoring site decreased by 85% between the peak year 2011 to 66 per site in 2022.

Particulate pollution was particularly high in March and April 2011 due to a combination of secondary pollution being formed over mainland Europe and wind conditions carrying this pollution to the UK. A period of low wind conditions followed which allowed emissions from UK sources to build up in the atmosphere, leading to unusually high concentrations of particulate matter [footnote 1]. Similar events occurred in February and April of 2019, resulting in a relatively high number of hours of PM2.5 pollution in that year.

5. Temporal variations in concentrations of PM2.5 in the UK, 2022

5.1 Monthly variations

The PM2.5 index shows the monthly mean, averaged over all included sites that had monthly data capture greater than or equal to 75% in a given year. The shaded areas represent the 95% confidence interval for the monthly mean concentration for roadside sites and urban background sites.

Figure 11: Monthly mean PM2.5 concentration at roadside and urban background sites, 2021

Figure 11: Monthly mean PM2.5 concentration at roadside and urban background sites, 2021

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For PM2.5 the highest concentrations in urban areas tended to occur during the spring and winter months in 2022. The greatest mean concentration in 2022 was in March (16.9 µg/m3 for roadside sites and 16.5 µg/m3 for urban background sites). A peak in early spring is typical for PM2.5 concentrations, as elevated concentrations of nitrates are transported from agricultural operations across continental Europe - AQEG report.

The next highest concentrations for both site types were in January and December. Residential combustion of wood and coal in stoves and open fires is a large contributor to emissions of particulate matter both in the UK and across Europe, and is a contributing factor towards elevated concentrations in winter months. Emissions from this source are typically located closer to urban background sites than roadside sides, which may explain the slight convergence between concentrations recorded at urban background and roadside sites throughout the winter months.

It should be noted that there are a large number of emission sources for particulate matter, and there may be other sources which contribute to this pattern. There can also be considerable contribution from sources originating outside of the UK. The level of transboundary derived particulates is determined by weather conditions and prevailing winds.

5.2 Hourly variations

The PM2.5 index shows the hourly mean, averaged over all included sites that had data capture greater than or equal to 75% for all instances of that hour in a given year. The shaded areas represent the 95% confidence interval for the hourly mean concentration for roadside sites and urban background sites.

Figure 12: Hourly mean PM2.5 concentration at roadside and urban background sites, 2022

Figure 12: Hourly mean PM2.5 concentration at roadside and urban background sites, 2022

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PM2.5 concentrations were greater in the evening compared to other times of the day; in 2022 the greatest mean concentrations were at 9pm for roadside sites (10.0 µg/m3), but at 10pm for urban background sites (9.4 µg/m3). This is thought to be the result of households burning wood, coal or other solid fuels in stoves or open fires for heating in the evenings, particularly in winter months.

6. Sections in this release

Summary

Background to concentrations of air pollutants

Concentrations of nitrogen dioxide

Concentrations of ozone

Days with ‘Moderate’ or higher air pollution (includes sulphur dioxide)

Compliance with the Code of Practice for Statistics and Defra group Statistics quality principles, and recent changes to the publication

Statistical tables (ENV02 – Air quality statistics)