USEPA's National Air-Toxics Assessment: Emissions and Cancer Risk Analysis in Cook County, IL

The USEPA’s National-Scale Air Toxics Assessment (NATA) is an ongoing comprehensive evaluation of 177 Clean Air Act toxics and diesel particulate matter in the US. NATA includes national emissions data from outdoor sources, estimations of ambient exposure concentrations, human exposures, and characterization of public health risk due to inhalation. Evaluation of the 2005 NATA results was performed in order to determine geographical areas, pollutants, and emissions sources that can be targeted for further reduction, and compare cancer risks for Benzene and Formaldehyde based on measured data at three fixed-site air monitoring stations in 2005 to those based on modeled EPA’s 2005 NATA estimates using both the traditional NATA approach and the EPA Superfund guidance approach. Illinois county level emissions results in 2005 showed that Cook County had the highest emissions estimates than any other county in Illinois, contributing to 25% of the total emissions. The source category contributions indicated that point source emissions dominated the total emissions in rural counties, while mobile source emissions dominated urban environments. In Cook County, the chemicals that contributed the most to overall emissions included toluene (22%), methanol (10%), m-xylene (7%), 2,2,4-Trimethylpentane (6%), and benzene (6%). While the top chemical contributors to cumulative inhalation cancer risk in Cook County were formaldehyde (39%) and benzene (12%), a significant majority of the 90th percentile inhalation cancer risks associated with these two chemicals concentrated along major highways and in the vicinity of O’hare airport. The benzene results based on all three risk calculation techniques were similar, with the NATA underestimating the risk in the Schiller Park air monitoring location and overestimating the risk in the Chicago location. The formaldehyde cancer risk estimates based on air monitoring data for Schiller Park were substantially higher than their respective modeled risk estimates in the 2005 NATA. The results concluded that although EPA’s NATA was very beneficial for performing air quality as well as excess cancer risk analysis spatially for certain chemicals, they should only be used to evaluate relative risks across different geographic areas.