UC Riverside Study Forecasts Most Heavy-Duty Nitrogen Oxides (NOx) Emissions Reductions Will Come from Improved Internal Combustion Engines, Regardless of EV Adoption

A May 2025 study published by a team of researchers from University of California, Riverside (UCR) shows outsized emissions reduction effects of replacing older heavy-duty diesel engines with new diesel or natural gas models, regardless of EV adoption. The study, “The impacts of improving heavy-duty internal combustion engine technology on reducing NOx emissions inventories going into the future,” is California-specific in terms of projected fleet composition and toxic nitrogen oxides (NOx) emissions through 2050, but the implications are valid nationwide.

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