New high resolution maps of estimated background ambient NOx and NO2 concentrations in the U.K.

Maps of estimated annual mean background surface concentrations of NOx and NO2 in the U.K. have been calculated on 1 km x 1 km grid for 1994. These maps have been calculated using a multi-stage approach which includes the interpolation of rural measurements and the empirical modelling of the local source contribution to ambient concentrations. The empirical regression models were calibrated with reference to automatic monitoring data and then validated by comparison with diffusion tube measurements of NO2 at several hundred sites. Estimates of the population potentially exposed to annual mean concentrations of pollutants above certain thresholds were calculated from these maps. These threshold annual mean concentrations can be approximately equated with proposed and existing air quality standards for NO2, benzene and 1,3 butadiene. These estimates indicate that about 8% of the population live in regions where the annual mean NO2 concentration is above the European Union Directive Guide Value for a median concentration of 26 ppb; about 23% live in areas at risk of exceeding the U.K. Government proposed 99.9th percentile target for NO2 of 104.6 ppb and about 30% live in areas with running annual mean benzene concentrations exceeding 1 ppb.