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Many local councils use diffusion tubes to measure nitrogen dioxide (NO2) as they are relatively cheap, easy to use, don’t require any power supply and can give a good indication of air pollution levels.

The low cost allows many of them to be used, so a picture can be built up across a large area. Non-professionals such as environmental campaigners and schools are also using them because the tubes require only limited attention and are easy to operate.

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Measuring Nitrogen Dioxide Using Diffusion Tubes

Under the provisions of the 1995 Environmental Act, all local authorities in England and Wales are required to assess air quality against a set of national targets for seven key pollutants. Some locations, exclusively next to very busy roads, particularly at junctions and where there are inclines on the highway and buildings close to the kerb, levels of nitrogen dioxide (NO2) may exceed the national objective.

Environmental Protection has identified these specific locations and undertakes routine monitoring for concentrations of nitrogen dioxide at the locations.


What are diffusion tubes?

The tubes are small and made of plastic with a cap at each end. Inside the top end of the tube is a metal disc coated with a substance that reacts with nitrogen dioxide to form a new chemical which remains trapped on the tube. The tube is placed vertically in a holder, usually attached to something like a lamppost or drainpipe, and the bottom cap is removed allowing air to diffuse into the tube.

The diffusion tube is left at the site with the bottom cap removed for a month. After this time the tube has the cap replaced and is taken to a laboratory for analysis. Each tube then provides an average concentration of nitrogen dioxide for that month. The monthly results are then averaged over 12 months to give an annual mean.

Air Quality Monitoring In Schools


A number of schools are now assisting the council in its monitoring programme, with diffusion tubes located on their premises. Each month we ask the participating schools to take readings from the diffusion tubes and the data colleted forms part of our reporting on air quality in the borough.

Your school can take part too! If you are interested in joining our team of schools, please follow the link below.

 :: more on Diffusion Tubes in Schools

Diffusion Tube online GIS information

An interactive map showing Nitrogen Dioxide (NO2) Diffusion Tubes diffusion tube locations and annual mean nitrogen dioxide concentrations is now available for you to view online.

The map is an interactive geographical information system which allows you to view and inspect map-based information for the Dudley area. Tools are provided to allow you to zoom and pan around the map, and ‘point and click’ to view information about features on the map.