Federal environmental regulators announced Thursday that more of Utah needs to reduce wintertime pollution.

As state officials look for ways to cut fine particulate pollution in the next few years, three more counties -- Box Elder, Cache and Tooele -- potentially face vehicle emissions tests to help control the microscopic soot that sometimes fouls the winter air in northern Utah's basins for weeks at a time.

Already, the Wasatch Front counties -- Salt Lake, Davis, Weber and Utah -- use emissions testing as a pollution-cutting tool.

Thursday's announcement identifies areas that violate the Clean Air Act's limits for PM 2.5. These final "nonattainment" areas in Utah include all of Salt Lake and Davis counties, portions of Cache, Utah, Weber, Box Elder and Tooele counties, plus a portion of Franklin County, Idaho, that is part of Cache Valley's airshed.

"PM 2.5 levels in Utah communities can have considerable impacts to human health," said Carol Rushin, EPA Region 8's acting regional administrator. "Designating areas as nonattainment will lead to the development of a plan to reduce air-pollution emissions and bring cleaner air to the Wasatch Front."

The state Division of Air Quality and federal regulators have been wrangling over the final boundary for nearly three years. Earlier this year, the state Legislature and then-Gov. Jon Huntsman Jr. were joined by Utah Republicans in Congress -- U.S. Sens. Orrin Hatch and Bob

Bennett and Rep. Rob Bishop -- in protesting the EPA's assertion that parts of rural Utah counties are contributing to the PM 2.5 problem.

In the end, EPA accepted only some of their advice.

Bennett vowed Thursday to assemble the data necessary to prove EPA wrong.

"This decision is not only unnecessary but also unjustified," he said in a news release. "I will continue to work with the state and the counties to correct EPA's data as quickly as possible."

Cheryl Heying, director of the air-quality division, noted that her agency was able to persuade EPA to shrink the boundaries a bit, but not as much as the state believes is warranted.

"We feel the science," she said, "does not support their conclusion."

Nonetheless, Heying's staff began working immediately on solutions to the crackdown that seemed inevitable once EPA announced it was lowering the allowable limits for PM 2.5 nearly two years ago.

Now her agency has three years to come up with a workable plan.

Solutions could include expanding the state's vehicle emissions-testing program, though Heying said that was not a foregone conclusion. Also possible is tightening the limits on industrial polluters, such as the Nucor Steel plant north of Brigham City.

But Heying said some pollution reductions are expected from fuel-efficient automobiles and from updating farm machinery, school buses and other diesel vehicles with equipment that emits less pollution.

"It's going to be a lot of little things will add up," she said. "No stones will be unturned."

Michelle Hofmann, co-president of the advocacy group Utah Moms for Clean Air, noted that pollution is a growing problem for many northern Utahns.

"This [EPA] action forces us to work on air pollution," she said. "It's very proactive."

fahys@sltrib.com