If you thought the EPA 2010 diesel exhaust emissions rules were the last you’d ever hear about reducing the nitrous oxide levels coming out of your trucks’ exhaust stacks, take a deep breath of clean air and think again.

Earlier this week, the U.S. Environmental Protection Agency announced that, in response to petitions filed by several states, including New York, Connecticut, Washington, Rhode Island, Massachusetts and Vermont, as well as cities with persistent smog problems such as Los Angeles and San Jose, Calif., it would begin work on a new proposed rule aimed at setting lower standards for NOx diesel emissions from heavy-duty diesel engines beginning in model year 2024.

EPA said the initiative is in keeping with its Clean Air Act mandates, which require it to revise standards occasionally to ensure it is doing everything possible to protect public health. The agency noted it has been 16 years since it last revised its NOx standards for heavy-duty diesel engines.

Industry response to the announcement centered on the Truck and Engine Manufacturers Association (EMA), which announced it would cooperate with EPA and the California Air Resources Board to determine if new regulations are warranted and can be implemented in a fashion that keeps costs and exhaust complexity at a minimum for North American fleets and other end users.

“Currently, we don’t know the answer to those questions and we need data to help us understand what improvements are possible,” said Jed Mandel, EMA president. “We are willing to cooperate and work in conjunction with anyone in the industry to address these issues.

"We do think there is some room for improvement on the current regulations," he continued. "And we want to have a hand in the process because if there are going to be new standards, we feel it is much better for our members to have one Federal standard to contend with, as opposed to several individual state standards spread out all over the country.”

Mandel said he agrees with EPA’s estimate that it will take at least two years to research the potential for new regulations and come up with a reasonable path forward to attain them, should they become law.

“We have a lot of work to do on this initiative,” he noted. “But my sense at the moment is there may be several, little things we can do in real-world trucking operations that will satisfy the EPA’s desire for further NOx reductions without putting undue strain on fleets and other businesses that depend on diesel trucks.”

Sean Waters, director of regulatory affairs and product compliance for Daimler Trucks North America, told HDT that the OEM “will collaborate with EPA, CARB and other stakeholders on potential future NOx regulations and work to ensure that such reductions do not jeopardize future CO2 and fuel economy reductions.”