From the Document: "Emissions from diesel engines--especially particulate matter (PM), nitrogen oxides (NOx), sulfur oxides, and air toxics--have been shown to contribute to air pollution that adversely impacts public health and welfare in the United States. Since 1970, the Clean Air Act (42 U.S.C. §7401 et seq.) has required the federal government to limit these emissions, among others, from new stationary (industrial) sources and new mobile sources. In the decades since, the U.S. Environmental Protection Agency (EPA) has promulgated emission standards for a variety of source categories, including new heavy duty highway and nonroad diesel engines. [...] Congress enacted the 'Diesel Emissions Reduction' program in the Energy Policy Act of 2005 (EPAct 2005, P.L. 109-58, Title VII, Subtitle G §§791-797; 42 U.S.C. §§16131-16137). It authorized EPA to administer a national and state-level grant and loan program to promote emissions reductions from legacy diesel engines. Through the Diesel Emissions Reduction program (as amended), EPA has provided loans, grants, and rebates to projects that use certified engine configurations and verified technologies, or that develop and commercialize emerging technologies, in order to replace legacy diesel engines."
CRS In Focus, IF11331
Congressional Research Service: https://crsreports.congress.gov/