WASHINGTON – The Trump administration has spent this year unwinding enforcement of emissions controls on diesel trucks.
In January, the Justice Department stopped criminally prosecuting anyone who distributes, manufactures or installs “defeat devices” – hardware or software that disables or bypasses a vehicle’s emissions system.
In July, President Donald Trump pardoned nine people convicted of such crimes, which violate the Clean Air Act, a landmark environmental law enacted in 1970.
One of the pardons involved a business that brought in $4.3 million over two years by remotely disabling software on diesel trucks that monitors pollution control hardware. The business charged up to $4,500 per truck for the service.
The owner was sentenced to four months in prison and a $25,000 fine.
“From the comfort of his home, this defendant caused environmental damage across the country, tampering with pollution controls on diesel trucks so that they spewed 30 to 1,200 times the pollutants of a legally configured truck,” said the prosecutor in Tacoma, Washington.
Public health advocates and environmental activists denounce the administration’s retreat from aggressive enforcement of emissions cheaters.
“These standards are only as good as their enforcement,” said Laura Kate Bender, vice president of nationwide advocacy and public policy at the American Lung Association.
Medium- and heavy-duty trucks made up just 6% of vehicles but were responsible for 59% of on-road nitrogen oxide emissions and 55% of particle pollution, she said, citing a 2020 study.
“If we are seeing more and more vehicles that aren’t running their emissions controls, that is going to lead to pollution that could have been prevented,” Bender said.
Only three metro areas have worse ozone pollution than Phoenix, according to the American Lung Association.
Will Humble, executive director of the Arizona Public Health Association and a former director of the Arizona Department of Health Services, said the “much more narrow” enforcement focus means the Trump administration can undermine the law without going through a formal rulemaking process that could take up to two years.
“They have a softer touch when it comes to enforcing the Clean Air Act. But that’s a discretionary thing. It doesn’t change the rules. It doesn’t change the regulations,” Humble said.
But what one president can do, the next can undo.
So, Humble said, he doesn’t expect a long-term negative impact – unless the next president has a similar agenda.
To Barry Pierce, one of the men Trump pardoned, the regulations are too onerous.
The Idaho resident pleaded guilty in 2023 to tampering with devices required under the Clean Air Act. His business, Gorilla Performance, removed the emissions control devices from trucks, then reprogrammed the on-board diagnostic (OBD) systems so they wouldn’t recognize the change.
He was sentenced to four months in prison and a $1 million fine.
Pierce said that many owners can’t afford to repair an emissions system that could easily cost $13,000 on a truck.
“Most people cannot afford to spend $13,000 once a year, or every other year, just to put that vehicle back into compliance,” he said by phone. “The problem is the EPA forcing these vehicle manufacturers to put the system in without really doing any testing to make sure these things work correctly. Because once they fail – and they will fail – they’re guaranteed to fail.”
Pierce now runs a business cleaning diesel particulate filters, which lets trucker owners save several thousand dollars compared to buying a replacement.
How the rollback works
Before the Biden administration, Clean Air Act enforcement was generally pursued through civil actions rather than criminal prosecution.
In January, Acting Attorney General Todd Blanche – the No. 2 official at DOJ at the time – signed an order instructing federal prosecutors to drop any pending criminal cases and cease opening new ones related to emissions tampering.
The memo stated that these violations were still open to civil penalties.
The American Lung Association’s 2025 “State of the Air” report found more than four in 10 Americans live in a county with a failing grade for ozone or particle pollution.
Diesel engines are still a major source of the smallest, most dangerous particles. Nitrogen dioxide reacts with sunlight to form ground-level ozone, or smog. Other compounds, especially nitrous oxide, also contribute to climate change.
The health risks fall hardest on children, older adults, pregnant people, outdoor workers and anyone living near a highway, warehouse or distribution hub, Bender said. Arizona is home to two major freight corridors, Interstate 10 and Interstate 40.
Phoenix-area air quality has improved dramatically over the past three decades even as Maricopa County’s population grew from roughly 2.2 million to 4.5 million.
Humble credits that to Clean Air Act requirements and improvements in vehicle technology driven mainly by consumer demand rather than EPA mandates. But commercial trucks have not improved as fast as private vehicles.
“If people are finding ways to get around them, it’s resulting in people getting sick who didn’t have to,” Bender said.
While critics blast the Trump administration for backing away from aggressive enforcement of flagrant Clean Air Act violations, defenders welcome the relief from restrictions they view as unworkable for truckers and fleet operators.
“Imagine being a manufacturer that’s created a really great product, maybe even a really, really popular product. Now, in perpetuity, you’re worried about whether or not a federal agency is going to come knocking on your door,” said Karen Bailey-Chapman, senior vice president of public and government affairs at the Specialty Equipment Market Association, the largest aftermarket car part association. “That’s not a way to position American manufacturing or especially American small businesses.”
Bailey‑Chapman said aftermarket parts manufacturers don’t object to compliance but have struggled with a lack of clear and consistent rules.
By law, parts that modify an emissions system are legal if they don’t make a vehicle dirtier than its original emissions profile, she said, but the EPA’s guidance has been confusing as to what would cross the line.
SEMA has developed its own emissions testing and compliance program to give manufacturers a consistent standard. EPA told the group July 1 that manufacturers can rely on SEMA testing to certify compliance with anti-tampering standards.
“We’ve always underscored that the law is still the law. So defeating an emission system is still illegal,” Bailey‑Chapman said.
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