Last December, the Environmental Protection Agency finalized its emissions standards for heavy-duty vehicles as part of its Clean Trucks Plan, clean air regulations that aim to reduce greenhouse gasses (GHG) and pollutants from the transportation sector. This new rule is the first time pollution standards for buses, semi-trucks, and commercial delivery trucks have been updated in more than 20 years.

The main focus of the new standards is nitrogen oxides (NOx), irritant gasses released by gasoline and diesel engines. Regulations tackling the reduction of other GHG emissions (like carbon dioxide and methane) would follow in the spring, EPA Administrator Michael Regan told The New York Times. Revised GHG standards for all heavy-duty vehicles might not start until the model year 2030.

When heavy-duty vehicles emit NOx, they “react in the atmosphere to form pollutants like fine particulate matter and ozone,” says Noelle Eckley Selin, professor in the Institute for Data, Systems, and Society and the Department of Earth, Atmospheric, and Planetary Sciences at the Massachusetts Institute of Technology. “These pollutants are damaging to human health, as they lead to cardiovascular and respiratory issues.”

[Related: The EPA wants more ‘renewable’ fuel. But what does that actually mean?]

Heavy-duty vehicles contribute about 23 percent of GHG emissions from the transportation sector, making them the second-largest contributor only behind light-duty vehicles like cars. New vehicles, starting with the model year 2027, are required to comply with the updated clean air standards. The EPA says the new regulations are more than 80 percent stronger than the current ones, which also cover a broader range of the vehicle’s operating conditions.

For instance, NOx emissions are high when vehicles idle or operate in stop-and-go traffic—so-called low-load conditions that aren’t subject to current emission standards. Yet these low-load operations are estimated to account for most of the vehicle’s NOx emissions during a typical workday, which is why the scope of the new standards will include them as well. The new rule also requires manufacturers to make sure that emission control systems function properly and aren’t prone to tampering by the drivers.

According to the EPA, the new rule can reduce the NOx emissions of heavy-duty vehicles by 48 percent in 2045. By then, the agency expects the pollution reduction to have provided substantial health benefits, resulting in 18,000 fewer cases of childhood asthma, 3.1 million fewer cases of asthma and allergic rhinitis symptoms, and 78,000 fewer lost days of work.

Emission reduction in the transportation sector would not only reduce health burden, but also support environmental justice and equity, says Eri Saikawa, associate professor of environmental sciences at Emory University. Heavy-duty diesel vehicles cause a disproportionate impact on people of color and low-income communities because they are more likely to live or attend school near major roadways, resulting in greater-than-average exposures to these pollutants.

[Related: Urban sprawl defines unsustainable cities, but it can be undone.]

To mitigate air pollution and climate change, Saikawa emphasizes the need to also reduce emissions of black carbon, a short-lived but potent climate pollutant that heavy-duty vehicles produce as well. It is not yet clear if black carbon emissions would be addressed in the updated EPA regulations to come.

Even though air pollution in the US has significantly improved over the past decades, Selin says it remains harmful at current levels. Additional policies, especially those striving for net zero goals, would have plenty of potential to reduce other aspects of air pollution. “Efficiency improvements and emissions reductions will be important, but ultimately addressing the impacts of climate change and air pollution together will require zero-emission alternatives,” she adds.

The White House has major federal actions in place that will accelerate and advance the use of clean heavy-duty vehicles. The production of new technologies like zero-emission heavy-duty trucks is also expected to increase in the near future, helping support the effectiveness of the Clean Trucks Plan.

“This is a difficult sector to decarbonize, and this will require innovations in technology as well as new policy actions,” says Selin. Coordinated efforts to tackle the sector’s environmental impacts, she adds, will be vital to ensure those affected by air pollution receive the “greatest possible benefit.”