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Data Provider: Welsh Government Air Quality Indicators
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General description

Air Quality Exposure Indicators - average NO2, PM2.5 and PM10 concentrations across local authority areas and health board areas, derived from modelled data for each square kilometre in Wales, measured in µg/m3 (DEFRA data)

Data collection and calculation

Each year the UK Government’s Pollution Climate Mapping (PCM) model calculates average pollutant concentrations for each square kilometre of the UK. The model is calibrated against measurements taken from the UK’s national air quality monitoring network.

The Welsh Government has used this published data to assign a concentration of NO2, PM2.5 and PM10 to each residential dwelling in Wales based on which square kilometre of Wales it sits in.

For each census output area (statistical geographic units comprising around 150 properties), the pollutant concentrations associated with each dwelling within it were averaged to give an average NO2, PM2.5 and PM10 concentration across the census output area.

For each Local Authority and Local Health Board, a population-weighted average over its constituent census output areas were calculated to give an average NO2, PM2.5 and PM10 concentration based on where people live in those Local Authorities and Health Boards. The same calculation was also repeated over all census output areas, to give a comparable figure for the whole of Wales.

Frequency of publication


Data reference periods

Annual average

Users, uses and context

Information is used for local area air quality management and monitoring.

Rounding applied

Population weighted concentrations are rounded to the nearest whole number (µg/m3).

Revisions information



Air Quality Exposure Indicators

Last update

July 2022 July 2022

Next update

November 2023 (provisional)

Publishing organisation

Welsh Government

Source 1

Air Concentration, Department for Environment, Food and Rural Affairs

Source 2

Small area population estimates (SAPE), Office for National Statistics

Source 3

Geographical information, Welsh Government

Contact email



Lowest level of geographical disaggregation

Local authorities

Geographical coverage


Languages covered

English and Welsh

Data licensing

You may use and re-use this data free of charge in any format or medium, under the terms of the Open Government License - see


Air quality, pollution, air concentration

Statistical quality

See weblinks.
Each year the Pollution Climate Model (PCM) which underpin the background maps is refined and improved ( to account for latest available science and understanding e.g. changes in emissions factors, improved activity data etc.). These method changes are usually only applied in the latest year's figures.
2021 air quality figures are based on 2020 population estimates.