WASHINGTON >> Pollution from diesel trucks, buses and cars globally is more than 50 percent higher than levels shown in government lab tests, a new study says.

That extra pollution translated to another 38,000 deaths from soot and smog in 2015, the researchers estimated.

The work published Monday in the journal Nature was a follow-up to the testing that uncovered the Volkswagen diesel emissions cheating scandal. Researchers compared the amount of key pollutants coming out of diesel tailpipes on the road in 10 countries and the European Union to the results of government lab tests for nitrogen oxides.

They calculated that 5 million more tons was being spewed than the lab-based 9. 4 million tons. Governments routinely test new vehicles to make sure they meet pollution limits.

Experts and the researchers don’t accuse car and truck makers of cheating, but say testing is not simulating real-world conditions.

“The paper shows how much human failure costs,” said Jens Borken-Kleefeld, a transportation scientist at the International Institute for Applied System Analysis in Austria who wasn’t part of the study.

The researchers included a team from the International Council on Clean Transportation, a nonprofit research and advocacy group, that arranged the testing that first showed VW diesel cars were rigged to cheat on emissions tests. They used previously published tests of pollutants coming from thousands of vehicles, all models, to calculate the extra pollution in 2015. Worldwide, three-quarters of that extra pollution is from trucks and buses.

Other research connects soot and smog to heart and lung diseases, with pollution killing more than 4 million people every year around the world, said lead author Susan Anenberg, a researcher at Environmental Health Analytics and a former U.S. government scientist.

The researchers calculated that the extra nitrogen oxides were responsible for about 31,400 deaths in 2015 because of tiny soot particles in the air and 6,600 deaths from extra smog. The European Union, which has mostly diesel cars, had an extra 11,500 deaths; China, 10,600; India, 9,300; and the United States, 1,100.

In Europe, new truck regulations are working and much of the excess pollution is coming from cars, said study co-author Ray Minjares of the clean transportation group.

Diesel in California

Diesel trucks are the largest source of air pollution in Southern California’s ocean-to-mountains air basin, experts say.

Southern California has made tremendous progress reducing smog since the 1970s, but the region still doesn’t meet federal health standards.

Monday’s study results arrive on the heels of a decision last month by California lawmakers to ease diesel truck emissions rules as part of the political horse-trading needed to pass a gas-tax hike, said Penny Newman, executive director of the Center for Community Action and Environmental Justice, based in Jurupa Valley.

Under the new law, trucks that meet California rules cannot be required to retire or upgrade their rigs until their machines are either 13 years old or have traveled at least 800,000 miles, and some truck owners are able to operate their rigs here for up to 18 years.

It also makes rules for sea ports, rail yards, warehouse-distribution centers and government fleets to use cleaner trucks more vulnerable to legal challenges, the regional air quality officials have said.

The change will greatly slow down air-pollution cleanup efforts, Newman said.

Joe Lyou, an air district board member and President and CEO of the Coalition for Clean Air, said he was not surprised that the latest study found that diesel pollution is underestimated.

“Studies at UC Riverside have also shown that our local trucks emit more air pollution than presumed because they spend a disproportionate amount of time hauling heavy loads in slow traffic,” Lyou said in an email.

Air district officials are counting on the Trump administration to require more stringent emissions standards for new diesel trucks. “It has been 17 years since the EPA revised heavy duty truck emission standards,” Lyou said. “We now have new clean alternatives to heavy-duty diesel trucks. The study shows why we need a new, more protective truck emissions standard.”

But not everyone agrees. Some business leaders fear that clean-air technology places them at a disadvantage.

“There is no absolute path to ‘quote’ clean emissions technology. There is nothing out there that is commercially viable,” said Weston LaBar, executive director of Harbor Trucking Association, a group representing port trucking companies. He maintains that zero-emissions electric trucks don’t have the power to haul full containers and natural-gas big rigs, once touted as the answer, have failed to deliver as promised.

The ports of Los Angeles and Long Beach — the largest fixed source of diesel pollution in the region — are in the middle of updating their decade-old anti-pollution plan.

During that time, the ports have made significant strides in sharply reducing diesel particulate matter in large part due to the curbs they put on diesel truck emission. Pushing for further reductions in dirty air, the port has replaced many machines on the docks with cleaner-running alternatives and officials are looking to eventually make the port nearly emission free.

Yet, for now, experts report that rates of asthma and other respiratory problems near the ports remain higher than many other parts of Southern California.

“It’s the reason why we are doing the work that we are doing,” said Heather Tomley, director of environmental planning at the Long Beach port. “We recognize there are negative impacts from these sources of pollution.”

A 2015 USC study showed that Southern California children — over a 20-year period — had fewer respiratory problems as a result of improved air quality.

﻿﻿Staff writers David Danelski and Rachel Uranga contributed to this report.﻿