Air quality - Monmouthshire

Current air quality

For up to date information on current air quality across Wales, including Monmouthshire, please visit the Welsh air quality website.

Local air quality management

Environmental Health monitor air pollutant levels to assess current and future air quality. This information is used to determine whether we are meeting the air quality objectives of the UK National Air Quality Strategy.

The strategy plans to improve air quality based on reducing concentrations of seven key pollutants. We are responsible for carrying out this strategy and will work with local people, commerce, industry, environmental groups, Natural Resources Wales and the Welsh Government.

There are seven pollutants listed in legislation that come under the Local Air Quality Management Regime, and they each have air quality objective levels that should not be exceeded.

Review and Assessment of local Air Quality:

Monmouthshire County Council’s Environmental Health section undertake review and assessment of the air quality within the county by undertaking monitoring at specific locations that might be at risk of having high levels of pollutions.

This data is collected and analysed and then published on this website every year in an annual progress report.

The current Annual Progress report is the 2023 edition, which presents the monitoring data for January to December 2022.

A link to the report is available in the List of available reports, further down this page.

Where annual monitoring and local intelligence shows a persistent exceedance of an air quality objective at a location with relevant public exposure, an Air Quality Management Area (AQMA) can be declared. If necessary, before declaring an AQMAs, more detailed assessments can be undertaken, such as air quality modelling and source apportionment studies, to determine if an air quality objective has been exceeded and the extent and reason for the exceedance.

If an Air Quality Management Area has been declared the council produces an Action Plan to identify measures that can be put into place to try and improve the air quality and achieve the objective level.

Air Quality Management Areas

Previous monitoring has identified that the only pollutant at risk of exceedance within the county is nitrogen dioxide from vehicle emissions. As such the majority of monitoring is undertaken along the road networks that run close to sensitive receptors like houses, schools, hospitals, and other areas where people may gather such as shopping centres and parks.

As a result of the monitoring there are currently two areas in the county that have exceeded the nitrogen dioxide objective level in the past and have therefore been declared Air Quality Management Areas.

These are Bridge Street in Usk and part of the A48 in Chepstow which includes Hardwick Hill. Both of these AQMA’s have Action Plans, and a link to them is available below.

List of available reports

Nitrogen dioxide and health

For information about how exposure to high levels of nitrogen dioxide and other key air quality pollutants, can effect health please visit the Welsh air quality website.

Air quality monitoring

In Monmouthshire the major source of pollution is from road transport sources, therefore we monitor for the three key pollutants associated with vehicle emissions, these are nitrogen dioxide, PM10 and PM2.5.

PM10 & PM2.5

PM10 and PM2.5 are the very fine particulates that can be carried deep into the lungs. Currently there are no exceedances of PM10 or PM2.5 objectives in Monmouthshire.

Nitrogen dioxide

The air quality objectives for nitrogen dioxide are:

Annual – 40 micrograms per cubic metre (µg m-3)

Hourly – 200 micrograms per cubic metre (µg m-3) not to be exceeded more than 18 times a year

The annual objective level is being exceeded in locations along Bridge Street in Usk and Hardwick Hill in Chepstow.

Types of monitoring

We use two types of monitoring for nitrogen dioxide concentrations along our road networks and one type for PM10 and PM2.5.

Nitrogen dioxide diffusion tubes

Diffusion tubes are small and relatively inexpensive and do not need a power supply, therefore we can fix them to lamp posts and houses in many locations in Monmouthshire to build up a good monitoring network close to where people live. Nitrogen dioxide in the air enters the tubes and gets absorbed onto a filter. Every month an officer changes the tubes and they are analysed in a laboratory.

Currently there are 41 diffusion tube monitoring sites in Monmouthshire located in Abergavenny, Monmouth, Usk and Chepstow. We have previously undertaken monitored in Raglan, Magor and Undy, however as levels were below the objective levels the tubes were re-located to more at risk locations.

Automatic monitoring

Automatic monitoring is a more expensive, but more accurate way to measure air quality. We currently have one automatic monitoring station located on Hardwick Hill in Chepstow. This unit is capable of continuously monitoring several pollutants. Current air quality data monitored by the automatic monitoring station in Chepstow can be found by visiting the Welsh Air Quality website and selecting Chepstow from the map.

There are three analysers in the monitoring station which monitor the key vehicle emission pollutants:

Nitrogen dioxide and nitric oxide

PM10 (small particles less than 10 µm diameter)

PM2.5 (small particles less than PM2.5 diameter)

Nitrogen dioxide is monitored with a chemiluminescent analyser and PM10 and PM2.5 are measured with TEOM-FDMS analysers. The monitors allow comparison with the annual, 24 hour, and hourly objectives.

Bias adjustment of nitrogen dioxide diffusion tube data

As the nitrogen dioxide automatic monitor is more accurate than the diffusion tubes we undertake a co-location study by exposing 3 diffusion tubes next to the Chepstow automatic monitor. The diffusion tube results can then be adjusted to take the difference into account. To make the tubes more accurate we also use data from other councils who undertake co-location studies around the UK.