An analysis of both the current levels and general trends of two major air pollutants (smoke and SO2) for the County of Merseyside has been attempted. The difficulties associated with use of the National Survey monitoring sites (as published by the Warren Spring Laboratory) to resolve values and trends on this county scale are described. The highly flexible nature of the co-operating body scheme by which most air pollution monitoring in the U.K. is undertaken results in extremely 'noisy' data especially in the light of continuing improvements in air quality and the changing emphasis and priorities in pollution control programs. It is also emphasized that evaluation of meteorological variables on this spatial scale is extremely questionable although it appears that temperatures can be well represented by a typical station's record. All discussions of air pollutants: levels, control and dispersion on the county-scale should be treated with considerable caution.