The current National Air Toxics Assessment (NATA) is based on 2002 national data. It modeled 180 of the 187 Clean Air Act air toxics plus diesel particulates from stationary and mobile sources. According to EPA, "[t]he purpose of the national-scale assessment is to identify and prioritize air toxics, emission source types and locations which are of greatest potential concern in terms of contributing to population risk." NATA estimates that most people in the United States have an average cancer risk of 36 in one million. This means that, on average, approximately 1 in every 28,000 people could contract cancer as a result of breathing air toxics from outdoor sources, if they were exposed to 2002 emission levels over the course of their lifetime. It also estimates that 2 million people (less than 1 percent of the total U.S. population based on the 2000 census) have an increased cancer risk of greater than 100 in 1 million. Benzene from mobile emissions (mostly cars and trucks) is still considered the largest contributor to the increased cancer risk.