EPA emissions inventory and cancer risk data for criteria pollutants and air toxics show clearly that vehicles and small stationary sources emit a majority of the air pollution nationally and account for most of the cancer risks from air toxics. Industrial sources, by contrast, rarely account for more than 10% of cumulative cancer risks from all outdoor sources of air toxics. The observed pattern of emissions is replicated at spatial scales ranging from census tracts to the nation as a whole. The secondary status of industrial facilities as sources of air pollution largely neutralizes the potential for pollution trading programs to cause hotspots. In the vast majority of jurisdictions, industrial emissions are simply too low, and in the few jurisdictions in which disparities cannot be ruled out, targeted policies exist to prevent them without compromising market efficiency. These findings are generalizable to all market-based regulations.