In a move aimed at reducing air pollution, Gov. Gavin Newsom on Friday signed a law that for the first time will require most large trucks in California, including 18-wheel tractor trailers, to pass a regular smog check.

Already, cars and passenger vehicles that are six years old or older are required to pass a smog check every two years. But large trucks, a major source of diesel soot and other air pollution, have not been required to pass inspection.

On Friday, Newsom signed Senate Bill 210, which requires the California Air Resources Board to set up a pilot program over the next two years and after that put rules in place for truck smog checks.

“Just as car owners have to get their own personal cars smog checked every two years, so too should truck operators be required to maintain their emissions controls so that we can ensure long-lasting air quality improvements,” said State Sen. Connie Leyva, D-Chino, who wrote the bill.

Heavy-duty trucks operating in California account for nearly 60 percent of the emissions of nitrogen oxides (NOx) — one of the main chemicals that causes smog — from mobile sources and are the largest source of diesel particulate pollution in the state.

Environmentalists say the new law will reduce emissions of soot and other contaminants, which contribute to high asthma rates in California, especially for people who live near freeways.

“This is the biggest air quality bill of this year,” said Bill Magavern, policy director for the Coalition for Clean Air, an environmental group with offices in Los Angeles and Sacramento.

“It’s something we have needed for years,” Magavern said. “Diesel trucks are the single biggest source of air pollution in California.”

He added. “The trucks can emit almost 10 times as much pollution as they are supposed to emit. So we need inspections and maintenance to keep their pollution levels down to where they were when the truck was new.”

But trucking industry officials say the rules are unnecessary because of other truck engine rules already in place or being phased in over the next few years. They also say they are concerned that the new law may allow state officials to take private data from trucking companies if the state program requires trucks to share information in the on-board computers that track truck emissions and other data.

Information kept in those on-board computer systems includes how far the trucks were driven, when they were driven, how fast they went, braking details and other information, said Joe Rajkovacz, a spokesman for the Western States Trucking Association, based in San Bernardino County.

“It is proprietary data,” he said. “Under the guise of environmentalism they want to grab people’s data.”

He said, “It brings up interesting privacy issues. Law enforcement can’t grab your cell phone at a traffic stop and go through it without a warrant. This is troubling to a lot of people.”

The new law applies to trucks that weigh more than 14,000 pounds. That includes delivery trucks, dump trucks,18-wheel tractor trailers, tanker trucks, farm trucks and others. The law does not include buses.

Approximately 12 million people in California live in communities that exceed federal health standards for ground level ozone, or smog, and particulate matter. Many are in the Central Valley and Southern California, which have some of the nation’s highest asthma levels. Other areas with high asthma levels include communities near ports, such as Oakland and Long Beach.

Rajkovacz noted that the California Air Resources Board already does regular tests for smoke from trucks at weigh stations and trucking companies. And under landmark rules finalized several years ago, the board required that by 2023, only trucks that are model 2010 or newer can be driven on California roads. That rule was required because older trucks pollute far more than newer trucks, but it was fought vociferously by the trucking industry.

“Once bureaucracy has its hooks in an industry, it never lets go,” he said. “It becomes a huge jobs program for public employees. They keep layering on costs.”

The law was supported by the American Lung Association, the American Heart Association, the American Cancer Society, the Bay Area Air Quality Management District, Sierra Club California, the Union of Concerned Scientists and other health and environmental organizations.

It was opposed by the Western States Trucking Association, the California Farm Bureau Federation, California Cattlemen’s Association and several other industry groups.