Illegal Tampering by Diesel Pickup Owners Is Worsening Pollution, E.P.A. Says

“That is an astronomically high level of smog-forming pollution,” he added. “It’s happening at ground level where people are breathing the fumes. And if the problem extends to other vehicles it’s almost unimaginable what the health impact will be.”

The E.P.A.’s Office of Civil Enforcement, which is largely staffed with career civil servants, has been conducting the investigation into diesel tuners for about five years, since it discovered the cheating by Volkswagen. An E.P.A. official familiar with the report, who spoke on condition of anonymity because he was not authorized to speak on the record, said it represents a significant milestone in the ongoing investigation.

The report was completed last week, though the E.P.A. has not publicized it or issued a news release, which stands in contrast to the media blitz assembled by the Obama-era agency for the Volkswagen investigation. In this instance, word got out after Evan Belser, the deputy director of the office’s Air Enforcement Division, emailed a copy of the report to the heads of three state air pollution control organizations.

A spokesman for the E.P.A., James Hewitt, initially said Wednesday that he was unfamiliar with the report. In a statement emailed after he was informed of it, Mr. Hewitt said, “Under our National Compliance Initiative, in FY 2020, E.P.A., resolved more civil tampering and aftermarket defeat device cases (31) that prevented more motor vehicle emissions (14.6 million pounds) than in any prior year in the agency’s history. Additionally, E.P.A. has assessed more in civil penalties, criminal fines, and restitution under this administration than the first four years of the Obama administration.”

The report studied only diesel pickup trucks weighing between 8,500 pounds and 14,000 pounds, but E.P.A. analysts believe the cheating has spread across American garages and highways.

“One reason it is difficult to estimate the full extent of tampering nationwide is that the Air Enforcement Division has reason to believe this conduct occurs within most or all categories of vehicles and engines, including commercial trucks, passenger vehicles, pickup trucks, motorcycles, forestry equipment and agricultural equipment,” the report concluded.

“The aftermarket defeat device problem is huge,” said Phillip Brooks, a former E.P.A. emissions investigator who worked on the diesel tuner investigation and the Volkswagen case. “A lot of people just don’t understand what the problem is — your average person buys a vehicle and says, it’s my vehicle, I can do what I want with it. They may not even be aware that these devices are illegal.”