On Friday, the metropolitan area became the first in the nation to get a clean bill of health from the Environmental Protection Agency for five of the six federal air quality standards.
Sulfur dioxide levels are still not in compliance, but that didn't stop officials from cheering the progress made against Denver's "brown cloud."
"What once seemed a mile-high task is now reality," EPA administrator Christie Whitman said. "Years after invoking tough policies and programs to dramatically improve its air quality, the Denver metro area now stands as a model for other large cities fighting their own battles against air pollution."
"You truly can breathe more easily today," she said.
With Gov. Bill Owens looking on, Whitman approved the final paperwork that will return the metro area to full compliance with the National Ambient Air Quality Standards. She said only Los Angeles still has problems as serious as those that once faced Denver.
The achievement was lauded by environmentalists. "Denver's air quality progress is an enormously important success and demonstrates that concerted public and private action can achieve cleaner, healthier air," Vickie Patton, senior attorney for Environmental Defense, said in a statement.
The Denver area has spent more than three decades trying to eliminate layers of pollution and particulates that hovered above the city and suburbs on winter days, part of a seasonal air inversion.
The state passed rigid auto inspection laws, required oxygenated fuels in polluted areas and banned wood burning in fireplaces on high-pollution days. Voluntary car pools and alternatives to sand on icy roads also helped.
Bob Doran, a 78-year-old former truck driver who has lived in the Denver area since 1951, said several friends moved away 14 years ago because they had breathing problems from the pollution.
Doran, breathing with the help of an oxygen tank, said the air has been considerably better the past three years.
"We used to have this foul crud in the air. It's better than it used to be," he said.
Patton said Colorado's rapid population growth could put the region in violation of a new federal rule on the level of ozone, a byproduct of vehicle emissions and power plants. The standard has been the subject of legal challenges by industries.
Since 1970 federal standards have measured carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter and sulfur dioxide, all of which harm human health.