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 region. Such simple rankings may be misleading for a number of reasons, including: