Fortnightly average NO2 concentrations have been measured at 49 sites in the small city of Lancaster, U.K., over a continuous 1-year period using passive diffusion tubes. At sampling sites on a congested main road in the city centre considerable spatial and temporal variability in concentrations was found. An annual mean concentration of 63 μgm−3 was found witha range of 12–222 μgm−3. The mean concentration in an adjacent main road was 58 μgm−3 with a range of 5–107 μgm−3. Rather less variability was seen in a suburban main road and in a suburban residential street, which had annual mean concentrations of 38 and 30 μm−3, respectively. Concentrations in a city centre pedestrian precinct decreased with distance from the main road, having an annual mean value of 30μm−3. The data suggest that the precise location of a sampling device may be crucial in determining whether or not a given NO2, concentration or standard is exceeded.