California Air Resources Board Advances Zero-Emission Initiatives

Environmental initiatives have long been a focal point for the state of California. Leveraging its unique position under the Clean Air Act, which allows the state to request a waiver from the Environmental Protection Agency (EPA) to implement emissions regulations exceeding federal standards, California continues to push ambitious environmental policy. This year’s efforts include two key regulatory initiatives led by the California Air Resources Board (CARB): the Advanced Clean Fleets (ACF) regulation and amendments to the Small Off-Road Engine (SORE) regulation.

California Air Resources Board
Figure 1: The ZEV Milestone Option schedule for transitioning internal- combustion-engine (ICE) truck fleets to near-zero-emission vehicles (NZEV) or zero-emission vehicles (ZEV). Graphic courtesy of the author

The ACF is part of California’s overall push to zero-emission trucks, and the SORE regulation focuses on reducing emissions from engines used in outdoor power equipment, such as leaf blowers and chain saws. If enacted, these policies will take effect in 2024, with potential consequences for businesses, including those in the tree care industry.

Advanced Clean Fleets

On April 28, CARB approved the Advanced Clean Fleets regulation. The ACF requires companies with more than $50 million in annual revenue, or those operating 50 or more vehicles within California, to begin transitioning their internal-combustion-engine (ICE) truck fleets to near-zero-emission vehicles (NZEV) or zero-emission vehicles (ZEV) starting in 2024. The ACF provides companies with two pathways to achieve compliance. Fleets can follow a Model Year Schedule, which allows existing trucks to be used until their end of useful life, as defined in regulation. Or, they can opt in to the ZEV Milestone Option for more flexibility.

Under the Model Year Schedule, companies can add only ZEVs to their California fleet past January 1, 2024. Starting January 1, 2025, those using this compliance option must begin phasing out their ICE vehicles. They must do this either by the start of the calendar year following the vehicles reaching their useful-life mileage threshold or by January 1 of the year when the vehicle exceeds 18 years of age, whichever occurs first.

Conversely, the ZEV Milestone Option requires companies to progressively convert their fleets to ZEVs between 2025 and 2042, depending on the vehicle’s classification type. For example, chipper trucks, classified in Milestone Group 1, must start the ZEV transition earliest. (Figure 1)

When adapting fleets, it’s vital to recognize that the ACF permits NZEVs, such as hybrid vehicles, to fulfill the purchase requirements for either compliance path until 2035. From 2035 onward, only ZEVs will satisfy the purchase criteria.

Exemptions and extensions

Although the above regulation may impose financial strains on companies operating within California, CARB will not enforce these new emission standards for out-of-state vehicles with ICEs. Consequently, the regulation only applies to vehicles operated in California, enabling affected TCIA members with operations in and outside of California to transfer ICE vehicles out of state to maintain compliance. Other exemptions or vehicle-delivery-delay extensions are further detailed within the regulation, subject to fulfillment of relevant requirements, reporting and recordkeeping.

Reporting and recordkeeping requirements

To enforce the ACF regulation, CARB will require fleet owners to submit a compliance report annually by February 1, starting in 2024. These extensive reports must include detailed information about the company and its fleet, and can be submitted online through the CARB ACF webpage at Exemption or extension requests requiring documentation, on the other hand, must be submitted via

Status and next steps

While CARB adopted the ACF regulation in April 2023, the Office of Administrative Law (OAL) has yet to approve the regulation. Meanwhile, CARB is forming a Truck Regulation Advisory Committee (TRAC) to identify best practices for implementing the regulation consistent with the regulation language and facilitating constructive dialogue to address key issues related to rule-implementation.

Small off-road engines

The ACF regulation primarily targets larger companies, but CARB’s environmental efforts extend even further. Their Small Off-Road Engines regulation, finalized in August 2022, pending final authorization from the EPA, would limit engines produced for sale in California to those with zero exhaust emissions (ZEE) starting in model year 2024. This regulation affects essential equipment such as leaf blowers, lawn mowers and chain saws under 45cc.

Recognizing the impact on member operations, TCIA proactively engaged with CARB during the rulemaking process. In comments to the agency, TCIA expressed concern that the truncated timeframe for manufacturers to develop compliant equipment would translate to higher costs for tree care businesses. TCIA argued that a longer implementation timeline would achieve California emission-reduction goals while lessening the burden for small businesses, which comprise 90% of the tree care industry.

Despite our efforts and those of other industry associations to advocate for a balanced approach, CARB’s final regulation did not adequately address our concerns. It advances an aggressive ideology that overlooks the economic costs of regulation and the feasibility of implementing it.

Status and next steps for SORE regulation

The Clean Air Act permits California to seek authorization from the EPA to enforce its unique standards on nonroad engines, an exception to the general prohibition against states enacting emission standards for these types of equipment. The EPA announced on May 23, 2023, that it was reviewing CARB’s authorization request for the SORE regulation. The timeline for this review remains uncertain, but it’s worth noting that EPA has historically been deferential to California, approving most prior-authorization requests by the state.


Given the economic burden these rulemakings may present, Republican members of Congress have chimed in. Various bills are under consideration that could alter or hinder the implementation of these rules. For example, House Republicans have added language to the annual appropriations bill that would restrict the EPA from using its funding to approve CARB’s authorization request related to the SORE regulations. Other legislation, H.R. 1435, the Preserving Choice in Vehicle Purchases Act, which would amend the Clean Air Act to prohibit the adoption of state regulations that would eliminate the sale of motor vehicles with internal-combustion engines, also is pending.

As California businesses await the fate of these rulemakings, TCIA will keep members apprised of developments. Tree care companies subject to these rulemakings or considering implementing electric vehicles may find Christopher Lyon’s TCI Magazine August 2023 article, “How to Smooth the Road to Electric Work Trucks,” insightful. Additionally, online magazine viewers may access CARB ACF, ZEV Milestones Option, High Priority and Federal Fleets, ACT and SORE resources at their respective links.

To learn more about relevant regulations, legislative updates and pending litigation, follow TCIA’s social-media pages and keep up to date with our advocacy site,

Josh Leonard is a legislative assistant with Ulman Public Policy, TCIA’s Washington, D.C.-based advocacy and lobbying partner.

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