A comparison of nitrogen oxide (NOx) emissions from heavy-duty diesel, natural gas, and electric vehicles

As California finalizes an omnibus rule that will require a 90% reduction in nitrogen oxide (NOx) emissions from heavy-duty vehicles in the 2024–2027 timeframe, other states, including New York, New Jersey, and Massachusetts, have indicated that they will also adopt California’s rule. Meanwhile, the United States Environmental Protection Agency (EPA) has been directed by the White House to propose by January 2022 a stringent national standard for NOx emissions from heavy-duty vehicles (HDVs) that will apply nationwide starting around 2027. These proposals and plans continue a series of emissions regulations in the United States lowering NOx emissions limits from heavy-duty vehicles that began in 1985. These standards have been, and the new ones will be, technology neutral, meaning that they do not specify what technologies, including powertrains, manufacturers must use to comply but only that they must comply.

Diesel, natural gas, and electric heavy-duty vehicles can be designed and manufactured with the capability of complying with the ultra-low NOx limits envisioned in the next set of California and federal HDV regulations. But that is not to say that the outcomes for each are equivalent. This briefing compares the capabilities of these three powertrain types in meeting an ultra-low NOx standard across four key areas:

1. Feasibility. Will the technology be available in the timeframe of the regulation and can the technology be configured to produce ultra-low NOx in line with the limits of the regulation?
2. Cost. What is the incremental cost of achieving regulatory compliance and what is the cost-benefit analysis of a given technology?
3. Health impacts. How do the overall health impacts vary from technology to technology, even when the ultra-low NOx emissions standard is met?
4. Climate impacts. What are the climate benefits of the different technology solutions?

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