Power-station contributions to local concentrations of NO2 at ground level

New air quality guidelines and standards for the protection of human health have recently been produced by various UK and European advisory and regulatory bodies. The new standards for NO2 are more stringent than previously and have reawakened interest in the impact of NOx emissions from large point sources, such as power stations, on ambient concentrations of NO2 at ground level. Theoretical considerations of the main chemical and dispersion processes which determine the concentration of NO2 in ambient air and analysis of 75 site-years of monitoring data by meteorological category, time of day and time of year indicate that concentrations above the WHO hourly mean guideline of 104.6 ppb due to power-station plumes are extremely unlikely in the UK. This conclusion is supported by data from sites in the vicinity of power stations which show no exceedances of the WHO NO2 guideline with a dominant local power-station contribution.