ANCHORAGE, Alaska — Two Alaska groups on Tuesday sued the Environmental Protection Agency, saying officials missed a deadline for deciding whether the Fairbanks North Star Borough should be reclassified as seriously out of compliance with federal air pollution standards.

The EPA in November 2009 designated the Fairbanks North Star Borough moderately out of compliance.

The agency after six years was required to review progress, and if problems lingered, consider reclassification of Fairbanks to a serious non-attainment area, said attorney Kenta Tsuda of Earthjustice, an environmental law firm representing Citizens for Clean Air and the Sierra Club.

The reclassification, due at the end of June, did not happen, Tsuda said. Serious non-attainment would mean stricter requirements within a state plan to clean up Fairbanks air.

“The state is required to use ‘best available control’ measures,” Tsuda said.

The lawsuit was filed in Seattle, the EPA’s regional headquarters. The agency released a statement noting that, based on air quality monitoring results finalized in July, Fairbanks did not attain the fine particulate standard by the end of 2015.

“The EPA is now working on proposing reclassification of the Fairbanks nonattainment area to serious,” the agency said. “We continue to work closely with Alaska Department of Environmental Conservation and the Fairbanks North Star Borough to support their efforts to improve air quality and bring Fairbanks into attainment.”

Fairbanks’ air pollution problem in the winter is brought on by extreme cold and geography.

Temperatures reach 40 to 50 below zero. Fairbanks and the nearby city of North Pole are partially surrounded by hills that create a bowl effect. In a meteorological phenomenon known as an inversion, cold air along the ground can be capped by a layer of warmer air, trapping emissions.

The area regularly sees high levels of fine particulate, a mix of solid particles and liquid droplets that can be inhaled deep in the lungs.

Fine particulate is linked to heart attacks, decreased lung function and premature death. Children, the elderly and people with chronic disease are most susceptible.

Fine particulate levels around Fairbanks at times spike to the highest levels in the nation and regularly exceed federal limits.

The sources of particulate are wood- and coal-burning stoves, vehicles and coal-fired power plants, according to the lawsuit. Some Fairbanks residents burn wood as a cheaper alternative to expensive oil. They have fought attempts to ban inefficient wood-burning heating systems.

A state cleanup plan rejected measures that could help Fairbanks air, such as a ban on the sale of green wood, Tsuda said. That could change if the EPA designated Fairbanks as a serious nonattainment area.

“At the very least, the state has to look at those measures that they didn’t consider before,” he said.