Maricopa County Lets Fleets Earn Credits for Greener Vehicles
Published Date: 4/16/2026
Proposed Rule
Summary
The EPA wants to approve a new rule in Maricopa County, Arizona, letting fleet owners earn credits by upgrading their vehicles to cleaner ones. These credits can help big polluters balance out their emissions, making the air cleaner. If you have thoughts, speak up by May 18, 2026—this change could save money and boost air quality!
Analyzed Economic Effects
4 provisions identified: 2 benefits, 2 costs, 0 mixed.
Fleet owners can earn tradable credits
If you own or operate a fleet in Maricopa County, Rule 205 (revised May 21, 2025) lets you generate emission reduction credits (called MERCs) by permanently retrofitting or replacing on-road vehicles to lower NOX or VOC emissions. Those MERCs can be certified, issued as MERC certificates, and traded to stationary sources as federally enforceable offsets under the county's Nonattainment New Source Review program.
Stationary sources can use MERCs to comply
Major stationary sources in the affected Maricopa County nonattainment areas can use MERCs (from fleet reductions) as offsets to meet Nonattainment New Source Review requirements for ozone precursors (NOX and VOC). For the portions of Maricopa designated Moderate for the 2008 and 2015 ozone NAAQS, the major source threshold for VOC and NOX is 100 tons per year and the offset ratio is at least 1.15 to 1.
Generators face monitoring and reporting duties
To get MERCs certified under Rule 205, fleet generators must submit MERC applications, use the rule's specified methods to calculate reductions, and comply with ongoing monitoring, recordkeeping, and reporting so the Department can issue MERC certificates and ensure reductions are federally enforceable.
Rule applies only to ozone precursors, not PM10
Rule 205 applies only to on-road mobile-source reductions of NOX and VOC (ozone precursors) and explicitly cannot be used to generate NNSR offsets for the PM10 NAAQS. The SIP revision was submitted May 30, 2025 and the rule revision date is May 21, 2025.
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Key Dates
Department and Agencies
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