40 C.F.R. § 1074 app A to Subpart A of Part 1074
(a) This appendix describes EPA's interpretation of the Clean Air Act regarding the authority of states to regulate the use and operation of nonroad engines.
(b) EPA believes that states are not precluded under 42 U.S.C. 7543 from regulating the use and operation of nonroad engines, such as regulations on hours of usage, daily mass emission limits, or sulfur limits on fuel; nor are permits regulating such operations precluded, once the engine is no longer new. EPA believes that states are precluded from requiring retrofitting of used nonroad engines except that states are permitted to adopt and enforce any such retrofitting requirements identical to California requirements which have been authorized by EPA under 42 U.S.C. 7543 .
40 C.F.R. 1074 app A to Subpart A of Part 1074