A coalition of environmental groups filed a notice of intent to sue on Thursday, warning the U.S. Environmental Protection Agency it must hold Utah and Arizona accountable for missing deadlines to submit plans to clean up air pollution.

The announcement came just as a new layer of dirty air settled in over Salt Lake City in the latest winter inversion, a phenomenon in Utah's urban corridor caused by weather and geography.

The groups, led by the Center for Biological Diversity, filed the notice as the first step to legally challenge the EPA, said Robert Ukeiley, the organization's senior attorney. The EPA now has two months to act or a lawsuit will be filed, he said. The notice also asks that Arizona be held accountable for missing its deadline for an air quality plan for Pinal County.

Inversions hover over Salt Lake City as cold, stagnant air settles in the bowl-shaped mountain basins, trapping automotive and other emissions that have no way of escaping to create a brown, murky haze.

Doctors warn that breathing the polluted air can cause lung problems and other health concerns, especially for pregnant women and people with respiratory issues.

The legal filing comes a day after Utah's air quality board approved the plan it was supposed to submit last summer. Utah Air Quality Director Bryce Bird said the plan was delayed because of technical issues with the model being used, but should be submitted to the EPA in the coming weeks. That should prevent the filing of the actual lawsuit, he said.

The Utah plan lays out actions implemented in recent years, including a requirement that only environmentally friendly water heaters and certain consumer products such as hair spray and nail polish be sold. It also details an existing ban on wood burning on the worst air quality days and a requirement that chain burger restaurants add equipment to limit pollution when using contained ovens, or broilers.

Additionally, the plan explains how an estimated $98 million will be spent by private companies and the U.S. government to add emission-reducing equipment at refineries and rocket propelling manufacturers and replace old boilers at Hill Air Force Base, Bird said.

EPA spokesman Richard Mylott didn't return an email and phone call seeking comment Thursday. His message said he was out of the office because of the government shutdown. Arizona Department of Environmental Quality spokeswoman Erin Jordan declined comment, saying she can't comment on potential litigation.

Utah Gov. Gary Herbert said in a statement that officials recognize the need to improve air quality, which is why he recommended $100 million in his latest budget for the issue.

The state's air quality issues could get a new round of scrutiny if Salt Lake City is awarded the 2030 Winter Olympics. A decision by the International Olympic Committee is expected in several years.

Deeda Seed, a field campaigner for the Center for Biological Diversity, said residents are grateful that many Utah officials take the issue seriously but said the results are lacking. The coalition that also includes the Center for Environmental Health and the Utah Physicians for a Healthy Environment wants the EPA to issue a formal notice that Utah and Arizona missed the deadlines.

"This is really about holding the EPA accountable for the job it's supposed to do to protect our air," Seed said. "This about bringing attention to this issue. This is a critical time for us."