"The Clean Air Act requires EPA to regulate emissions of toxic air pollutants from a published list of industrial sources referred to as 'source categories.' As required under the Act, EPA has developed a list of source categories that must meet control technology requirements for these toxic air pollutants. The EPA is required to develop regulations (also known as rules or standards) for all industries that emit one or more of the pollutants in significant quantities. EPA developed implementation tools (eg. checklists, brochures) to help comply with the standards."
Read more at: Air Toxics: Rules and Implementation
For the list of hazardous air pollutants, the list of modifications, and guidance on pollutant aggregation, please see: