Report No. 9/14

25 Sep 2014

This report focuses on published studies that have examined the epidemiologic associations of ambient air exposures to nitrogen dioxide and the occurrence of acute and chronic health effects in humans. All relevant studies published since the World Health Organization issued their Air Quality Review in 2005 were taken into consideration. Nearly a hundred of the 240 studies examined for preparation of this report dealt with the relationship between NO2 exposures and acute respiratory disease or asthma exacerbation. This continues to be the heath outcome of greatest concern with NO2 and will likely garner the most interest in future research programs. Although a tremendous amount of new information has been gathered, there are still nagging issues that have not been sufficiently resolved to the extent needed to make definitive statements regarding causality and risk. Confounding and bias continue to plague many studies and the results from a limited number of new controlled human exposure studies suggest that NO2 may not be responsible for the many of the reported associations that have been reported with asthmatics. Until improved statistical and monitoring methods are developed there will continue to be considerable doubt about the relevance of results from studies using single pollutant modelling and exposure estimates from fixed monitoring stations.