Important Information: Comparing data from different monitoring sites

Please Note: The data we publish on this website include air pollution measurements at a range of different locations; some are at the roadside, whilst others are at background locations or in rural areas. There are clearly important exposure issues and potential health effects at roadside sites, as well as at urban background locations. It should be noted that - while the measurements at each site are made on a comparable basis and are factually correct - it would not be scientifically sound to make simplistic conclusions based on them to derive a ranking order indicating which towns are the most polluted in the UK. Such simple rankings may be misleading for a number of reasons, including:

• Background stations generally represent overall city-wide exposure more closely than do roadside sites
• Defra's network of monitoring sites does not cover all cities in the UK
• The results from single measurement points would need to be supplemented by modelling to describe fully the overall levels and resulting population exposure in a given town or city