In December, federal officials plan to designate Tacoma as the only city in Washington where concentrations of airborne soot exceed federal air quality standards, officials said Tuesday.

Also Tuesday, the Puget Sound Clean Air Agency announced a regional violation of a recently revised federal air quality standard for ground-level ozone, which also damages lungs. Federal officials are not expected to make that official until May 2010.

While ozone causes problems in summer, Tacoma’s soot problem is typically the worst in winter, and peaks on cold days when the air is still and residents crank up wood-burning stoves.

The soot compliance deadline is 2015. Specific regulations won’t be drafted until next year, and officials said they don’t know what effect they might have.

“It’s too early to tell,” said Gina Bonifacino, a EPA air quality planner in Seattle. “We don’t know yet.”

One strategy already in the works is a campaign to encourage owners of wood-burning stoves to change to cleaner methods of home heating. The Puget Sound Clean Air Agency kicked off a $204,000 program late last year. Earlier this month, the state Department of Ecology announced a $650,000 follow-up subsidy, also available to Tacoma-area householders.

Bonifacino said similar stove-swap programs elsewhere have produced significant air-quality improvements, enough to meet federal Clean Air Act standards. “If we get lucky, maybe that will do it,” said Alice Collingwood, a Clean Air Agency spokeswoman.

And before the EPA makes a final decision on Tacoma’s air, the agency plans to solicit public comment. The start of that 30-day comment period has not been scheduled, but it’s likely to begin in September, Bonifacino said.

The federal standard for fine particles was revised in 2006 to more effectively protect human health.

The standard governs particles 2.5 micrometers in diameter or one-thirtieth the size of a human hair. Although too small to detect without a microscope, together such particles form haze and impair visibility.

Medical research has shown that such tiny particles lodge deeply in human lungs, shorten lives and contribute to respiratory ailments.

In Tacoma, concern centers on a South End monitoring station, where a record going back several years shows particulate concentrations in excess of the current limit.

In 2006, when EPA revised its standard, the agency cut by nearly half the permitted amount of airborne soot: The 24-hour standard went from 65 to 35 micrograms per cubic meter.

The EPA’s proposal for Tacoma is based on a December 2007 recommendation from the state Department of Ecology. Federal officials also have endorsed the map of the so-called “non-attainment” area recommended by state officials in March.

The map includes all of Tacoma except Northeast Tacoma and Point Defiance Park, which were left out because state officials said those areas don’t contribute to the air-pollution problem.

The boundaries extend southeast from Tacoma to South Hill and Frederickson and include Lakewood, Steilacoom, Ruston, Fife, Edgewood, Puyallup, Spanaway and Parkland.

Susan Gordon: 253-597-8756