SACRAMENTO, Calif. (AP) — A California company will pay $1 million for violating federal environmental laws by making and selling devices that defeated smog controls on diesel trucks, prosecutors announced Tuesday.

Sinister Manufacturing Co., Inc. of Roseville, doing business as Sinister Diesel, pleaded guilty Tuesday to conspiracy and to violating the Clean Air Act by tampering with the monitoring device of an emissions control system of a diesel truck, according to a statement from the U.S. attorney’s office.

Prosecutors said that for nearly a decade, Sinister sold products referred to as “delete devices” or “defeat devices” that were designed to bypass diesel truck emissions controls, along with software that could alter a truck’s on-board computer so that it appeared to run normally.

The company “also counseled customers on how to evade state emissions tests,” the U.S. attorney’s office statement said.

Such devices, which have been sold by several companies, are promoted as increasing horsepower. Some diesel truckers have used them to intentionally spew big black clouds of diesel exhaust, which is known as “rolling coal,” environmental groups have said.

While Sinister marketed the devices as being geared for racing and off-road driving, the company knew most were used on public roads and at times a quarter of its gross revenue came from “delete” products, prosecutors said.

“EPA testing has shown that a vehicle altered with these parts can emit more than 100 times the amount of certain harmful air pollutants, compared to a vehicle with an intact emissions control system,” said Larry Starfield of the Environmental Protection Agency’s Office of Enforcement and Compliance Assurance.

An EPA report in 2020 found that more than 500,000 diesel pickup trucks in the country had been illegally deleted, the U.S. attorney’s office statement said.

Diesel emissions can contribute to respiratory ailments such as asthma and lung cancer, and one study attributed 21,000 deaths a year to diesel particulate matter, according to the statement.

“Environmental laws that control diesel pollution are especially important to protect sensitive populations such as the young, the elderly and people who suffer from respiratory conditions,” said Phillip A. Talbert, U.S. attorney for the Eastern District of California.

Sinister agreed to pay a $500,000 criminal fine and another $500,000 to settle a federal civil case. The company agreed it wouldn’t make, sell or offer to sell delete products.