Your Top 5 Questions on NOx Standards Answered


The Environmental Protection Agency (EPA) is preparing a rule that would set new standards to reduce NOx emissions from heavy-duty truck engines beginning in 2024. The agency last tightened its NOx standards for truck engines in 2010 to 0.2 gram per brake horsepower-hour.

The California Air Rescue Board is pushing for a lower NOx standard, as low as .02, so they can meet the federal ambient air quality standards for the ozone. That would be a 90% reduction in NOx emissions.

What is NOx? Nitrogen Oxides. NOx pollutes air with its chemical compounds. NOx represents a family of 7 compounds. The EPA regulates nitrogen dioxide, NO2, as a surrogate for this family of compounds because it’s the most prevalent form of NOx in the atmosphere and is generated by human activity.

Where does NOx come from? About half of the NOx emitted comes from automobiles and other mobile sources.

What other EPA rules affect trucking? The agency’s heavy-duty greenhouse-gas regulations will take effect in 2024. The GHG Phase 2 calls for cutting truck emissions of carbon dioxide (CO2) and other greenhouse gasses, but left the NOx levels alone.

What’s the challenge? There are tradeoffs in lowering NOx emissions: a higher combustion temperature drives fuel efficiency, but also creates more NOx. The EPA has been under pressure to reduce NOx emissions from heavy-duty trucks. Plus, limiting NOx and CO2 standards at the same time is an engineering challenge. The Truck and Engine Manufacturers Association president said, “It is especially important to ensure that any potential future low-NOx requirements do not compromise compliance with the just-finalized Phase 2 greenhouse-gas standards, which will improve heavy-duty on-highway fuel economy by more than 25% over the next 10 years.”

What does the industry think of the NOx Rule? The EPA’s future rule signals progress. Today, NOx levels are near zero, and with additional regulations, emissions will be even less. The American Trucking Association (ATA) wants the federal government, not states, to set NOx standards. “Further ramping down on NOx emissions as envisioned by this petition will likely have a deleterious effect on our industry’s overall fuel economy. We believe any tightening of NOx standards for large trucks might consider these impacts, as well as the impact these technologies may have on engine cost and reliability,” said ATA’s energy and environmental counsel. The ATA works with the EPA to improve the environment, like with the SmartWay Transport Partnership.


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