Earlier this year, the US Environmental Protection Agency (EPA) received several petitions from state and local government agencies from across the country and other organizations to increase the stringency of the on-highway heavy-duty engine NOx emission standards from 0.2 grams per brake horsepower-hour (g/bhp-hr) to 0.02 g/bhp-hr.
On 20 December, EPA formally responded, saying that it will initiate the work necessary to issue a Notice of Proposed Rulemaking with the intention of proposing standards that could begin in Model Year 2024. This timeframe is consistent with the lead-time requirements of the Clean Air Act, and is aligned with a milestone implementation year for the EPA heavy-duty Phase 2 GHG program. (In the final HD Phase 2 rule, EPA had noted the evidence supporting the need for more stringent national NOx emissions standards.)
EPA acknowledged a need for further NOx reductions from heavy duty on-road trucks, buses, and other vehicles to reduce adverse health impacts from ground-level ozone and microscopic airborne particles; that the Clean Air Act directs EPA to revise standards from time-to-time in order to protect public health; and that it has been 16 years since EPA last revised its NOx standards for heavy-duty highway engines.
Further, the agency said, technical progress has been made in developing technologies and approaches that can reduce NOx emissions beyond the standards put in place in the 2000 rule. As part of its technology analysis for the HD Phase 2 rulemaking, EPA identified cost-effective GHG reducing technologies, such as engine down-speeding and idle reduction technologies that also have the potential to achieve greater NOx reductions.
These technology examples, along with numerous cost-effective technological advances in exhaust after-treatment technologies, demonstrate that there are feasible approaches where GHG reductions and fuel efficiency do not have to be sacrificed to achieve greater NOx reductions.—EPA memorandum in response to petitions
EPA’s goal is to develop a program that could be adopted by EPA and the California Air Resources Board, creating a 50-state program, which would streamline compliance for manufacturers.
EPA said it will work with a broad range of stakeholders, including heavy-duty vehicle and engine manufacturers; the California Air Resources Board; labor groups; technology suppliers; environmental non-governmental organizations; state and local air quality agencies; truck dealerships; trucking fleets; and truck drivers and owners in developing the proposed rulemaking.