EPA Proposes Approving Arizona's Vehicle Upgrade Credits for Cleaner Air
Published Date: 4/16/2026
Proposed Rule
Summary
The EPA wants to approve a new rule in Maricopa County, Arizona, that lets fleet owners earn credits by upgrading their vehicles to cleaner ones. These credits can help big polluters meet air quality rules, encouraging cleaner air without extra costs. People have until May 18, 2026, to share their thoughts before the rule becomes final.
Analyzed Economic Effects
4 provisions identified: 3 benefits, 1 costs, 0 mixed.
Fleet Owners Can Earn Mobile Emission Credits
If you run a vehicle fleet in Maricopa County, you can generate emission reduction credits (MERCs) by permanently retrofitting or replacing fleet vehicles with lower-emitting models under Maricopa County Rule 205 (revised May 21, 2025). Those MERCs apply only to ozone precursors (NOX and VOC) and can be traded to stationary sources as offsets under the Nonattainment New Source Review (NNSR) program; the Moderate-area offset ratio is at least 1.15 to 1 and the major source threshold is 100 tons per year for NOX and VOC.
Generators Face Monitoring and Reporting Rules
Fleet owners who generate MERCs must submit applications, follow specified methodologies to calculate reductions, and comply with ongoing monitoring, recordkeeping, and reporting before the Department will issue MERC certificates under Rule 205. These procedures are required for generators to have their reductions certified as real, surplus, quantifiable, permanent, and federally enforceable.
Stationary Sources Can Use Mobile Credits for NNSR Offsets
Major stationary sources in the relevant Maricopa County nonattainment areas may use MERCs from on-road mobile sources to offset projected NOX or VOC emissions increases for NNSR permitting, subject to NNSR rules and the requirement that offsets be real, surplus, quantifiable, permanent, and federally enforceable. Rule 205 applies only to ozone precursors (NOX and VOC) and explicitly cannot be used to generate offsets for PM10 NAAQS.
Federal SIP Approval Would Make MERCs Federally Enforceable
The EPA is proposing to approve Maricopa County Rule 205 into the Arizona SIP; if finalized, MERCs generated under Rule 205 would become part of the federally enforceable SIP and must meet federal offset integrity criteria before an NNSR permit may be issued. The public comment period for this proposal ends May 18, 2026.
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