Diffusion tube data
Greater Manchester's air quality data
Click on the maps below to see the locations of hundreds of air quality monitoring diffusion tubes across Greater Manchester. These are used to monitor the amount of harmful nitrogen dioxide (NO2) in the air.
We collect and analyse two different sets of data and you can toggle between them using the buttons below:
This map shows data collected largely at busy roadside locations for the purposes of the Clean Air Plan. Nitrogen dioxide levels are measured against the long-term annual mean legal limit of 40μg/m3. For Clean Air Plan monitoring purposes, government criteria are that measurements at diffusion tube concentrations of 40.4μg/m3 and below are rounded down to 40μg/m3 and are within the annual mean legal limit.
This map shows data collected for the purposes of Local Air Quality Management. Monitoring takes place in areas where there is relevant public exposure to pollution, and includes locations such as homes, schools, hospitals and care homes. For Local Air Quality Management purposes, government criteria are that measurements at diffusion tube concentrations of 40.0μg/m3 and over are above the annual mean legal limit.
Nitrogen dioxide levels are measured against both the long-term annual mean legal limit of 40μg/m3 and a short-term hourly legal limit of 200μg/m3. Exposure to nitrogen dioxide has a cumulative impact over time and may contribute to chronic health conditions – similar to smoking.
How we use this data
Diffusion tube data is used to assess levels of NO2 in the air in Greater Manchester and for scientific modelling to predict future levels of NO2. Monitored air quality data is used to review and align the Clean Air Plan modelling which is validated by the government’s Joint Air Quality Unit independent review panel.
Clean Air Plan Monitoring – 2022
In 2022, NO2 air quality monitoring for the purposes of the Greater Manchester Clean Air Plan was carried out at 432 locations (210 more than 2021), with 95 sites of exceedance. A further 108 locations were considered to be at risk of exceedance*
*The number of monitoring sites in the Clean Air Plan survey increased in 2022 to provide greater coverage. Of the diffusion tubes that were in place in both 2022 and 2021, there would have been an additional five areas of exceedance in 2022 – up from 45 to 50.
Air quality key
30 or below
Very compliant (green)
Above 30 to 35
Compliant (yellow)
Above 35 to 40
At risk of exceeding legal limit (amber)
Above 40 to 60
Above legal limit (red)
Above 60
Well above legal limit (purple)