Estimating human exposure to nitrogen dioxide: an indoor/outdoor modeling approach

Adverse health consequences associated with human exposure to nitrogen dioxide are well documented. In order for policymakers to assess health risks and implement appropriate control strategies, accurate information is required concerning (1) the number of people exposed, (2) the severity and patterns of exposure, and (3) the health-related effects of exposure. In the past, data from central monitoring sites have been used to establish air pollution exposures. However, it is now recognized that people spend much of their time indoors or in areas away from fixed monitors where pollutant concentrations may be drastically different. An attempt to provide a more realistic estimate of nitrogen dioxide exposures is made. A simple deterministic model is developed, relating exposure to background ambient levels, indoor values, and human activities. Ambient and indoor parameters are derived from monitoring programs in six U.S. cities. Results suggest indoor nitrogen dioxide concentrations in private dwellings vary primarily with outdoor levels and type of cooking fuel, but are also affected by factors such as air-exchange rates and strength of indoor sources. Estimates of population exposures are obtained by combining observed distributions of nitrogen dioxide concentrations from outdoor and indoor settings with information about number of people and time spent in each microenvironment.