Coal-fired units at Xcel Energy’s 56-year-old Cherokee Generating Station in Adams County are gone — and with them almost 10 tons a year of air pollutants.

In their place, a new natural-gas-fired unit is under construction — a $530 million project.

This work at Cherokee is the biggest part of the $1 billion Clean Air-Clean Jobs Act program approved in 2010 to cut air pollution by closing and retrofitting Xcel coal-fired plants.

The program is expected to cut power-plant nitrogen oxides — an ingredient in regional ozone — by 86 percent.

The Front Range is exceeding federal health standards for ozone, and the state must submit a plan to the federal government on how it will get into compliance. Closing the coal plants is part of that plan.

Passage of the law creating the program and its implementation were battled for in the legislature and at the Colorado Public Utilities Commission.

It was opposed by the mining industry and independent power producers and supported by the natural-gas industry and environmental groups.

The Colorado Office of Consumer Counsel also voiced concerns about the impact of the program on bills.

The law offers Xcel, Colorado’s largest utility, financial incentives for closing aging coal plants. Xcel estimated the effect on rates would be about 2 percent.

“It is turning out to be a successful program,” said John Nielsen, energy program director at Western Resource Advocates, a Boulder-based environmental-policy group. “So far, everything is on time and on budget.”

Cherokee coal-fired units 1 and 2 have been demolished, unit 3 will operate until 2015, and unit 4 will be shut in 2017.

The Arapaho 3 unit in Denver is slated to shut by the end of this year, and a coal-fired unit at the Valmont Plant in Boulder will shut in 2017, according to Xcel.

In addition, $340 million in air-pollution controls are being installed at the Hayden Plant in Craig and the Pawnee Station in Brush.

“The program is moving along and meeting its goals,” Xcel spokesman Mark Stutz said.

In 2010, the two Cherokee units, now demolished, emitted 4,823 tons of sulfur dioxide and 4,488 tons of nitrogen oxides, according to federal Environmental Protection Agency data.

In June, the Obama administration announced that it would propose rules to curb emissions of carbon dioxide, a greenhouse gas linked to climate change, from power plants.

The closed Cherokee units also emitted 1.6 million tons of carbon dioxide in 2010, according to the EPA.

“One of the aims of Clean Air-Clean Jobs was to get out in front of future regulations,” Western Resource Advocates’ Nielsen said.

“If there are carbon-dioxide regulations, Colorado should get credit for Clean Air-Clean Jobs,” he said.

Mark Jaffe: 303-954-1912, mjaffe@denverpost.com or twitter.com/bymarkjaffe