Research and analysis

Benzo[a]pyrene (BaP) 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 benzo[a]pyrene (BaP) target value set for the protection of health.

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.

1. BaP pollution and its impacts

Polycyclic aromatic hydrocarbons (PAHs) are a large group of chemical compounds which usually occur as complex mixtures rather than as individual compounds.

PAHs are persistent, organic compounds with toxic and carcinogenic effects. Long-term inhalation of PAHs has been associated with a range of adverse effects, including respiratory effects such as breathing problems and lung damage, as well as heart disease and effects on the immune system.

One particular PAH, BaP is used as a ‘marker’ for this group of compounds. The International Agency for Research on Cancer (IARC) has classified BaP as causing cancer in humans. BaP is considered to be one of the most potent carcinogenic PAHs.

Other PAHs have been classified by IARC as probable or possible human carcinogens, as summarised in the UK Health Security Agency publication.

2. Sources of BaP pollution

The release of pollutants into the atmosphere is known as emissions. Annual UK emissions of benzene are estimated each year in the National Atmospheric Emissions Inventory (NAEI). The NAEI provides estimates of the total amount emitted during a calendar year. The latest estimates currently available are for 2024.

The NAEI reports emissions of BaP from human activities in the UK, but there are a few exceptions included as memo items, such as international shipping and forest fires. The information presented here does not include memo items.

Figure 1 shows the split of BaP emissions in 2024 between various sources. Domestic combustion was the largest single contributor of BaP emissions in 2024, followed by waste. Total UK emissions decreased substantially between 1990 and 2005, largely driven by reductions from industrial processes and product use.

Figure 1: UK annual emissions of BaP by 2024 major emission source: 1990, 2005, 2023 and 2024

Notes:

1. ‘Domestic combustion’ refers to households burning a variety of fuels, for example in stoves and fireplaces.
2. ‘Waste’ includes activities such as composting, landfill, sewage sludge decomposition and waste incineration.
3. ‘Industrial processes and product use’ refers to specific industrial production processes and the use of manufactured products.
4. Sources are ordered by emissions in 2024 from highest to lowest, excluding ‘Other’.
5. Further detail on emission source categories is available in the latest Methods for NAEI emissions data document.

3. Trends in BaP pollution

How BaP concentrations have changed over time since 2007 is shown in Figure 2. Average measured BaP concentrations have reduced from a peak in 2008 of 0.8 ng/m3 to 0.1 ng/m3 in 2025.

The average concentration has been calculated from all stations in the Polycyclic Aromatic Hydrocarbon (PAH) monitoring network that had an annual data capture greater than or equal to 75 per cent. The shaded areas represent the 90 per cent confidence interval.

Trends over time can be influenced by changes to the number of monitoring sites and their locations. The pattern shown here will therefore exhibit some effect of changes to the structure of the monitoring network over time.

Figure 2: Annual mean concentrations of BaP in the UK, 2007 to 2025

4. Spatial variation

Figure 3 shows modelled annual mean BaP concentrations in 2025 for each 1x1km grid square of the UK. The data comes from the CMAQ-Urban Model used for supplementary assessment against the BaP target value set for the protection of health, as set out in section 6. Higher concentrations of BaP tend to occur in more urbanised areas across the UK. The vast majority of the UK experiences BaP concentrations less than 0.1 ng/m3, and all grid squares were modelled to be less than 0.6 ng/m3.

Figure 3: Modelled annual mean BaP concentrations for 2025

Note that Figure 3 shows the modelled annual average background concentration of BaP in each 1x1km grid square of the UK. Within the grid squares, there may be local areas of higher concentration close to specific emission sources. These will not be visible in the background maps.

5. BaP target value

This section outlines the target value set for BaP concentrations.

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

Table 1: BaP compliance criteria

Description	Averaging period	Metric
BaP target value for health	Annual mean	1 ng/m3

Note 1: target value relates to the total content of BaP in the PM10 fraction.

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

6. 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 Air Quality Standards Regulations (2010) 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 the air quality compliance assessment 2025: results and data tables.

Monitoring

In 2025, there were 36 monitoring stations from the Polycyclic Aromatic Hydrocarbon (PAH) monitoring network which met the data quality requirements for assessment against the BaP target value. This includes:

• 23 background stations
• 2 roadside monitoring stations
• 6 industrial monitoring stations
• 5 rural background monitoring stations

Modelling

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

For assessment against the BaP target value, 2 model outputs were calculated:

• annual mean BaP concentrations for each 1x1km grid square of the UK
• detailed modelling was conducted at a finer spatial scale around industrial locations previously known to cause exceedances of BaP – this was used to confirm that there are no exceedances

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 the air quality compliance assessment 2025: results and data tables. 

7. Compliance Assessment for 2025

All zones were compliant with the target value for BaP concentrations in 2025.

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

8. Changes in compliance over time

This section provides information on non-compliances in previous years from 2008 onwards. The target value for BaP  was set in 2004 under the 4th Air Quality Daughter Directive, which was subsequently transposed into UK legislation by the Air Quality Standards Regulations (2010).

Figure 4 summarises the numbers of zones with exceedances of the target value for BaP in previous years. There was a maximum of 8 zones in exceedance in 2010 and 2012, which were attributed to emissions from industrial sources, but since then there has been a steady decline in the number of zones exceeding the BaP target value.

2024 was the first year where no zones exceeded the BaP target value, and this has remained the case in 2025.

Reports on measures are published providing more information on previous exceedances of the target value and the measures that were taken to address them.

Figure 4: Number of zones (out of 43) not compliant with BaP target value (2008 to 2025)