A review of the acute and long term impacts of exposure to nitrogen dioxide in the United Kingdom

This review addressed the distinction between the impact of nitrogen dioxide (NO2) on health from that of particles and the availability of concentration-response information for long term exposure to NO2. The results of animal studies suggest that damage to lung lining fluid may occur at concentrations of NO2 that are marginally higher than those in ambient air. Serious respiratory effects occur only at much higher concentrations. Peak concentrations are more important than longer term mean levels of exposure and, although damage tends to increase with duration of exposure, there is evidence of adaptation.The results of human volunteer experiments show that concentrations of NO2 that are slightly higher than in ambient air affect lung function, airways resposiveness, respiratory symptoms and the response of asthmatics to allergens. The power of epidemiological studies to determine a relationship between ambient NO2 and health has been weakened by the poor correlation between personal exposure and ambient concentrations and the importance of tobacco smoke as a source of NO2 exposure for smokers. The small apparent short term effect of NO2 on health appears to be independent of that of particles, but may partly due to some other unmeasured component of traffic pollution. Ambient NO2 in the UK may be associated with an increase in daily death rate and numbers of hospital admissions for cardiovascular or respiratory illness of less than 0.2% and probably less than 0.05%. There is limited evidence to suggest that the impacts of particles on daily death rate are enhanced by NO2. The results of studies of the long term effects of exposure to NO2 do not suggest an adverse effect.