MADISON, Wis. (AP) -

After four years and a lawsuit, the state Department of Natural Resources is finally ready to adopt federal air pollution standards.

The U.S. Environmental Protection Agency published new limits on fine particulate matter in January 2013. Wisconsin law requires the DNR to adopt rules matching EPA standards to ensure state permits meet federal requirements but the Republican-controlled agency didn't do it.

Environmental groups Clean Wisconsin and the Midwest Environmental Defense Center sued in 2014 to force the agency to comply.

The groups and the DNR quietly settled the lawsuit last year with an agreement calling for the DNR to get rules reflecting the federal standards into state code by March 31, 2017. Agency officials have now drafted the regulations and the DNR board is expected to adopt them at a Dec. 14 meeting and forward them to Gov. Scott Walker. If he signs off and no lawmakers object, the rules would likely go into effect in late March.

"We're glad to see DNR finally adding these health-based air quality protections to help address the many respiratory illnesses like asthma, bronchitis and emphysema that many Wisconsin residents face," said Amber Meyer-Smith, Clean Wisconsin's government relations director. "It's unfortunate that the DNR needs to be compelled to add these protections, but we're glad they're complying with the settlement timelines."

DNR officials said at the time the lawsuit was filed that they were working on drafting the rules but it was slow-going because the rule-making process requires the DNR to analyze the standards' economic impact. Agency spokesman Andrew Savagian said this week that Walker authorized the DNR to begin work on the rule in June 2015. He had no immediate comment on why work didn't start until the settlement was reached.

Fine particulate matter is a mix of small particles and liquid droplets made up of acids, organic chemicals, metals, soil or dust particles often found near roads, dusty industries or in smoke from forest fires or power plants. The particles can pass through the throat and nose and enter the lungs, causing health problems, according to the EPA. The federal rules revised the annual standard for the amount of particulate matter allowable in the air from 15 micrograms per cubic meter to 12 micrograms per cubic meter.

DNR officials wrote in a Nov. 7 memo to Secretary Cathy Stepp that all areas of the state are currently within the new standards. They solicited information about what effect adopting the federal standards would have on businesses and particulate matter sources from more than 1,600 stationary sources in Wisconsin and a half-dozen business associations, including Wisconsin Manufacturers and Commerce, the state's largest business group and a staunch Republican ally, and concluded the regulations would have little to no impact.

The 2015 settlement also required the DNR to adopt tighter restrictions the EPA set in 2010 for sulfur dioxide and nitrogen oxide. The DNR sent those rules to the Legislature in April 2015, shortly before the settlement was approved. They went into effect this August.

Savagian said that rule took so long because it was the first one the DNR's air program implemented under the economic impact requirement.

Sulfur dioxide is a gas produced from fossil fuel combustion at power plants and other industrial facilities. The gas has been linked to a number of respiratory ailments, according to the EPA. Nitrogen oxide results from vehicle emissions and contributes to smog. It can cause airway inflammation and exacerbate problems for asthma suffers, the EPA has said.

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