The U.S. Department of Justice said on Thursday ConocoPhillips, the largest domestic refiner, will pay a $4.5 million fine and spend $525 million to cut harmful air emissions from nine U.S. petroleum refineries in seven states.

Under the Clean Air Act agreement, ConocoPhillips - the No. 3 U.S. oil company - will pay the civil penalty and spend more than $525 million to install pollution control measures at its refineries.

It will spend at least an additional $10 million on environmental projects to further reduce emissions and support community activities to help reduce pollution.

The agreement was part of a consent decree filed in the U.S. District Court in Texas. Five states are involved in the settlement, which is a part of the Environmental Protection Agency’s national effort to reduce air emissions from refineries.

“This is the largest of 13 settlements the EPA has made with U.S. refiners,” said Thomas Skinner, assistant EPA administrator. “We now have legal agreements with companies representing more than half of domestic refining capacity.”

Under the agreement, ConocoPhillips is expected to reduce harmful air emissions by more than 47,000 tons per year from nine petroleum refineries in seven states. The affected refineries are located in Belle Chasse, La.; Linden, N.J.; Borger and Sweeny, Texas; Carson/Wilmington, Calif.; Ferndale, Wash.; Rodeo/Santa Maria, Calif.; Trainer, Pa. and Roxanna/Hartford, Ill.

The actions are expected to reduce annual emissions of nitrogen oxide by more than 10,000 tons and sulfur dioxide by more than 37,100 tons per year. Emissions of particulate matter are expected to be significantly reduced, Justice Department officials said.

The air pollutants addressed by the agreement can cause serious respiratory problems and exacerbate cases of childhood asthma, officials said.

“Today’s settlement with the largest petroleum refiner in America leads us closer to ensuring clean air compliance across the refining industry,” said Assistant Attorney General Thomas Sansonetti, who runs the department’s’ environment and natural resources division. “The department will continue to aggressively pursue these actions to reduce air pollution.”