This Article presents the first synthesis of geospatial data on toxic air pollution in the United States. Contrary to conventional views, the data show that vehicles and small stationary sources emit a majority of the air toxics nationally. Industrial sources, by contrast, rarely account for more than ten percent of cumulative cancer risks from all outdoor sources of air toxics. This pattern spans multiple spatial scales, ranging from census tracts to the nation as a whole. However, it is most pronounced in metropolitan areas, which have the lowest air quality and are home to eighty percent of the U.S. population.The secondary status of industrial facilities as sources of air toxics has important implications for the current debate over cap-and-trade regulation—the policy instrument of choice for controlling greenhouse gas (GHG) emissions responsible for climate change. Environmental justice advocates have opposed GHG trading in significant part because it could exacerbate inequitable exposures to toxic co-pollutants, not GHGs themselves, in minority and low-income communities.The likelihood of such disparities occurring has remained an open empirical question. The geospatial data reveal that, apart from a few readily identifiable census tracts, the potential for GHG trading to cause toxic hotspots is extremely low. Moreover, for the few jurisdictions in which disparities cannot be ruled out, targeted policies exist to prevent them without compromising market efficiency.
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