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Heavy-duty engines have been subject to emission standards for criteria pollutants, including particulate matter (PM), hydrocarbon (HC), carbon monoxide (CO), and oxides of nitrogen (NOx), for nearly half a century; however, current data suggest that the existing standards do not ensure full, in-use emission control. In particular, in-use engine NOx emission levels from heavy-duty vehicles can be significantly higher than their certified values under certain conditions. NOx emissions are major precursors of ozone and significant contributors to secondary PM2.5 formation. Ozone and ambient PM2.5 concentrations continue to be a nationwide health and air quality issue. Reducing NOx emissions from on-highway, heavy-duty trucks and buses is an important component of improving air quality nationwide and reducing public health and welfare effects associated with these pollutants, especially for vulnerable populations and in highly impacted regions. This action will evaluate data on current NOx emissions from heavy-duty vehicles and engines, and options available to improve control of criteria pollutant emissions through revised emissions standards. Additionally, this action will contain targeted greenhouse gas (GHG) reductions and evaluate ways to streamline existing requirements. This rulemaking will address significant public health and environmental justice concerns caused by pollution from internal combustion engines while supporting early introduction of zero emission technologies.

Statement of Need: This action follows petitions for a rulemaking on this issue from over 20 organizations including state and local air agencies from across the country.

Summary of the Legal Basis: CAA section 202(a)

Alternatives: EPA may request comment to address alternative options in the proposed rule.

Anticipated Costs and Benefits: Updating these standards will result in NOx reductions from mobile sources and could be one important way that allows areas across the U.S. to meet National Ambient Air Quality Standards for ozone and particulate matter. Updating the standards will also offer opportunities to reduce regulatory burden through smarter program design.

Risks: EPA will evaluate the risks of this rulemaking.