The list of hazardous air pollutants is made based on the Clean Air Act (CAA), a comprehensive federal law that regulates air emissions from stationary and mobile sources. CAA requires EPA to set emission standards for substances on the list of hazardous Air pollutants (CAA). CAA also stipulates that administrative departments shall minimize the discharge of hazardous air pollutants or prohibit their discharge volume when formulating the discharge standards for air pollutants.