Research and analysis

Arsenic 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 target value set for arsenic 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. Arsenic pollution and its impacts

Arsenic (As) is a metalloid which occurs naturally in the environment, in soils, rocks and minerals. Arsenic is emitted into the atmosphere in the form of particulate matter from both natural sources and human activities. A significant source is open burning of treated wood waste.

Arsenic occurs in organic and inorganic forms. Inorganic arsenic compounds are highly toxic, while organic forms are less harmful. Inhalation of air containing high levels of inorganic arsenic are reported to cause respiratory irritation and damage. Inhalation exposure is associated with carcinogenic effects.

For the general population, inhalation typically represents a minor route of exposure to inorganic arsenic, although cigarette smoke contains a large amount of arsenic.

2. Sources of arsenic pollution

The release of pollutants into the atmosphere is known as emissions. Annual UK emissions of arsenic 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 arsenic 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.

Figure 1 shows the split of arsenic emissions in 2024 between various sources. Waste was the largest single contributor of arsenic emissions in 2024, and the NAEI reports this is specifically from the open burning of treated wood.

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

Notes:

1. ‘Waste’ includes activities such as composting, landfill, sewage sludge decomposition and waste incineration.
2. ‘Industrial processes and product use’ refers to specific industrial production processes. This also includes the use of manufactured products, both industrial such as the use of solvents, adhesives and lubricants.
3. Sources are ordered by emissions in 2024 from highest to lowest, excluding ‘Other’.
4. Further detail on emission source categories is available in the latest Methods for NAEI emissions data document.

3. Trends in arsenic pollution

How arsenic concentrations have changed over time since 2004 is shown in Figure 2. Average measured arsenic concentrations have decreased from an annual mean of 1.1 ng/m3 in 1990, to 0.6 ng/m3 in 2025. The largest decline occurred between 2004 and 2008, but since then concentrations have remained relatively stable.

The average concentration has been calculated from all stations in the Heavy Metals 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 arsenic in the UK, 2004 to 2025

4. Spatial variation

Figure 3 shows modelled annual mean arsenic 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 target value set for lead, as set out in section 6 and 7. Figure 3 shows higher arsenic concentrations around more urbanised areas of the UK.

Figure 3: Modelled annual mean arsenic concentrations for 2025 

Note that Figure 3 shows the modelled annual average background concentration of arsenic 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. Arsenic target value

Table 1 outlines the target value set for arsenic concentrations.

Compliance against the arsenic 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: Arsenic compliance criteria

Description	Averaging period	Metric
Arsenic target value for health	Annual mean	6 ng/m3

Note 1: target value relates to the total arsenic content 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 19 monitoring stations from Heavy Metals Monitoring Network which met the data quality requirements for assessment against the arsenic target value. This includes:

• 7 background stations
• one roadside monitoring station
• 5 industrial monitoring stations
• 6 rural background monitoring stations

Further information on the monitoring instruments used for measuring arsenic are detailed in the Statistical Tables that accompany this release.

Modelling

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

For assessment against the arsenic target value, one model output was calculated: annual mean concentrations of arsenic (ng/m3) for each 1x1km grid square of the UK.

For more information on the modelling methods and for access to the data, please 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 arsenic 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 arsenic 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).

The UK has been compliant with the target value for arsenic since 2008.