The Environmental Protection Agency has approved a Maricopa County program allowing emissions credits generated by voluntary reductions from on-road vehicle fleets. The credits are intended to offset increases in emissions at major stationary sources under the county's nonattainment new source review permitting program.
EPA's final rule takes effect December 7, 2026. Approval establishes a framework; the notice does not report actual credits generated under it or measured future air-quality results.
How credits are intended to work
EPA approved county Rule 205 as part of Arizona's federally enforceable air plan. The agency says owners or operators that permanently reduce nitrogen oxide or volatile organic compound emissions from on-road fleets can trade the reductions with stationary sources seeking offsets for proposed increases under the nonattainment new source review permit program.
The rule provides for credits through retrofitting or replacing existing vehicles with lower-emitting vehicles, subject to other Clean Air Act requirements. EPA describes four creditability elements as surplus, permanent, quantifiable and federally enforceable reductions. It also cites the requirement that offsets be based on actual emissions of the relevant pollutant.
The agency describes requirements intended to support permanence. For example, it says a baseline vehicle must be permanently removed from the relevant nonattainment area or rendered permanently disabled and disposed of; it also describes monitoring, recordkeeping and reporting requirements.
The dispute in the record
EPA says it received comments from five separate commenters on its proposal: four supported it and one opposed it. According to EPA's summary, the opposing commenter argued that the Clean Air Act does not authorize the trade because such reductions do not meet permanence, quantification and enforceability requirements.
EPA disagreed, saying the statute does not prohibit using mobile-source reductions as offsets for stationary sources when applicable requirements are met. This report relies on EPA's published summary of the comments and response, not independent review of each submission.