WASHINGTON — The owners and operators of more than half a million diesel pickup trucks have been illegally disabling their vehicles’ emissions control technology over the past decade, allowing excess emissions equivalent to 9 million extra trucks on the road, a new federal report has concluded.

The practice, described in a report by the Environmental Protection Agency’s Office of Civil Enforcement, has echoes of the Volkswagen scandal of 2015, when the automaker was found to have illegally installed devices in millions of diesel passenger cars worldwide — including about half a million in the United States — designed to trick emissions control monitors.

But in this case no single corporation is behind the subterfuge; it is the truck owners themselves who are installing illegal devices, which are typically manufactured by small companies. That makes it much more difficult to measure the full scale of the problem, which is believed to affect many more vehicles than the 500,000 or so estimated in the report.

In terms of the pollution impact in the United States, “This is far more alarming and widespread than the Volkswagen scandal,” said Drew Kodjak, executive director of the International Council on Clean Transportation, the research group that first alerted the E.P.A. of the illegal Volkswagen technology. “Because these are trucks, the amount of pollution is far, far higher,” he said.

The E.P.A. focused just on devices installed in heavy pickup trucks, such as the Chevrolet Silverado and the Dodge Ram 2500, about 15 percent of which appear to have defeat devices installed. But such devices — commercially available and marketed as a way to improve vehicle performance — almost certainly have been installed in millions of other vehicles.

The report found “significant amounts of excess air pollution caused by tampering” with diesel pickup truck emissions controls. The technology is essentially an at-home version of the factory-installed “defeat devices” embedded into hundreds of thousands of vehicles in the United States by Volkswagen, which was forced to pay $14.7 billion in the U.S. to settle claims stemming from the scandal.

The report said “diesel tuners” will allow the trucks to release more than 570,000 tons of nitrogen dioxide, a pollutant linked to heart and lung disease and premature death, over the lifetime of the vehicles. That is more than ten times the excess nitrogen oxide emissions attributed to the factory-altered Volkswagens sold domestically.

The report also found that the altered pickup trucks will emit about 5,000 excess tons of industrial soot, also known as particulate matter, which is linked to respiratory diseases and higher death rates for Covid-19 patients.

“A global respiratory pandemic is the worst time to find out that there is this massive cheating by the makers of these devices,” said John Walke, an expert in air pollution law at the Natural Resources Defense Council, an advocacy group, noting recent studies linking higher levels of particulate matter pollution to higher rates of Covid-19.