ANCHORAGE — The U.S. Environmental Protection Agency announced Thursday it is proposing to accept a state of Alaska plan for cleaning up polluted winter air in Fairbanks even as the agency presses for more stringent measures.

The agency is recommending approval of the state plan addressing “moderate” nonattainment for fine particulate, said Tim Hamlin, EPA region 10 director of the Office of Air and Waste. A final decision is due Aug. 28.

With the Fairbanks area continuing to fall short of clean air standards, however, the EPA has proposed to reclassify the borough as in “serious” non-attainment, requiring a new plan.

“It’s clear that more is needed to be done to reach attainment,” Hamlin said by phone from Seattle.

Fine particulate is a mix of solid particles and liquid droplets that can be inhaled deep in the lungs. Fine particulate causes premature death in people suffering heart and lung diseases. It causes nonfatal heart attacks, according to the EPA, and increased visits to emergency rooms for people with respiratory or heart diseases.

The primary sources of particulate in Fairbanks, Hamlin said, are woodstoves and wood heaters used to warm homes. Wood is an alternative to expensive heating oil.

Extreme cold and geography contribute to the Fairbanks pollution problem. Hills surrounding Fairbanks create a bowl effect. During inversions, when cold air along the ground is capped by a layer of warmer air, emissions are trapped.

The environmental law firm Earthjustice, representing two groups, sued to force an EPA decision on the state plan. Earthjustice attorney Kenta Tsuda said by email he had not seen the decision document.

“If EPA has signed a proposed action, that’s good news because the Clean Air Act process has to move forward in Fairbanks,” he said.

The state plan for moderate nonattainment, Hamlin said, met requirements of the law that called for “reasonably available” emission control technologies. Among the elements are prohibitions on open burning, limits on the amount of smoke that can be emitted and prohibitions on burning wood that’s not seasoned.

A plan for serious nonattainment would require “best available” emission control technologies.

Down the road, if air quality in the borough is in serious non-compliance, and a state plan for cleanup is not working, the EPA could step in with a federal plan. Hamlin acknowledged that step likely is years away, even though people with heart and lung problems remain vulnerable.

“The reason we’re not talking about that and not emphasizing that is it’s far, far more effective for the borough and the state to be addressing this issue,” he said, especially when the pollution source is a lot of individual actions.

“It’s not a large, industrial point source that is the primary issue here,” Hamlin said. “It’s a lot of individual people trying to stay warm in the winter.”