South Louisiana has been left in a sort of limbo status since the U.S. Environmental Protection Agency sent mixed signals about the region's air quality.

Now, public health advocates are suing the federal government to try to force it to take decisive action and identify the areas with unsafe pollution.

The Baton Rouge area has ping-ponged in and out of ozone compliance as federal regulations have tightened. Low-atmosphere ozone, a contributor to smog, has been linked to respiratory ailments "much like a sunburn damages skin," as the EPA has characterized it.

Gas prices, power plants and the region's petrochemical industry are all impacted by efforts to control emissions, which are created by burning fossil fuels.

Former President Barack Obama's administration lowered the minimum acceptable ozone level from 75 parts per billion to 70 ppb in 2015. Baton Rouge was declared in compliance with the old standard just recently, but the EPA was supposed to identify which areas were compliant with the new threshold by Oct. 1.

That didn't happen.

Instead, last month, the agency named counties and parishes around the country that had attained an acceptable ozone level, while not listing others at all. Those left off the list include 11 Louisiana parishes — East and West Baton Rouge, Ascension, Livingston, Iberville, Pointe Coupee, East and West Feliciana, St. Helena, Assumption and St. James.

"We don't know what the thinking is because EPA didn't spell anything out. … We have not been given a directive," said Vivian Aucoin, senior scientist at the Louisiana Department of Environmental Quality.

The regional EPA office was no more clear when approached for an explanation for this story, issuing a three-sentence response about the 2015 National Ambient Air Quality Standards.

"On November 6th, EPA moved forward with final attainment designations (for 2015 ozone NAAQS) for nearly 90 percent of the country. For the remaining areas, EPA is not yet prepared to issue designations. EPA will issue designations at a later date," the agency wrote in a statement.

Groups such as the American Lung Association and the Environmental Defense Fund filed suit in California on Monday to get the courts to compel the EPA to definitively identify which areas aren't in attainment.

While the agency says 90 percent of the country has been addressed, many areas with a high degree of pollution are heavily populated. The Environmental Defense Fund argues that more than 100 million people are not being adequately protected because the EPA is dragging its feet and failing to identify nonattainment counties and parishes.

"Everyone in this country is entitled to breathe clean, healthy air," said Graham McCahan, an attorney for the Environmental Defense Fund.

He said he is hopeful EPA Administrator Scott Pruitt will fulfill his responsibility and require "the state of Louisiana to make a plan and address the sources of pollution."

The capital area is agonizingly close to being in compliance with meeting the air quality standards set for ozone levels. The threshold is 70 ppb and Baton Rouge stands at 71 ppb, Aucoin said.

Baton Rouge Area Chamber Executive Vice President Michael DiResto said he hopes the EPA will give the region a year or so to get down to the acceptable level.

"Obviously, we're moving toward improvement," he said. "It just does not make sense … to stifle our economy and our industry."

The Louisiana Mid-Continent Oil and Gas Association is hopeful the region won't be declared out of ozone compliance. Nonattainment means gas stations have to stock fuel that's chemically different from the gas that's sold elsewhere. It's more expensive to produce and can inflate costs by 10 cents to 15 cents per gallon, said Tyler Gray, attorney for the oil and gas association.

“The designation of non-attainment for the capitol region is problematic for a number of reasons. For the everyday consumer, it could mean an increased cost of gasoline during the summer of 2018," LMOGA President Chris John wrote in a statement. 

"We have been working at LMOGA with our members, along with regulators at the local, state, and federal level, to develop a body of work that shows the rationale for non-attainment is either isolated or the result of influences outside of the Baton Rouge metro area. Hopefully, this isn’t the final decision going into 2018 summer.”

When an area falls out of attainment, industrial sites also can't expand without taking measures to slash emissions at their existing facilities, Aucoin said. Businesses need to know where the federal government stands so they can plan ahead, DiResto said.

"I think, right now, what's really troubling is that we're in a period of uncertainty. ... It's a confused period," DiResto said.

For one, everyone is trying to figure out why places far removed from the industry like St. Helena didn't make the attainment list. Also, Assumption Parish is usually included in the Houma statistical area, while St. James typically gets lumped in with New Orleans, Aucoin said.

When will Louisiana get some kind of clarification?

"Your guess is as good as mine. … We ask that question on a daily basis," Aucoin said.

Generally speaking, she said, the parishes under scrutiny include East and West Baton Rouge, Livingston, Ascension and Iberville. That's why cars registered in those parishes have to have their emission controls checked when drivers apply for their inspection sticker, she said. Vehicle emission standards are regulated nationally, though.

Authorities have worried about ozone pollution for decades because the substance reacts with cells, particularly those that line the throat and lungs, according to LSU toxicology professor Vince Wilson.

Chronic exposure causes inflammation and irritation similar to smoking, though smoking has other deleterious health effects as well, he said.

Ozone doesn't usually cause acute health problems, but the cumulative effect over time can contribute to conditions like chronic obstructive pulmonary disease and forces the cardiovascular system to work harder to pump oxygen throughout the body.

The EPA has previously linked its efforts to keeping children healthy.

"EPA's updated ozone standards will improve public health protection for children, avoiding hundreds of thousands of asthma attacks beginning in 2025. … Repeated ozone damage to developing lungs can affect children into adulthood, contributing to permanent reductions in the lungs' ability to function," the agency wrote in an online fact sheet.

Ozone high in the atmosphere is beneficial because it blocks ultraviolet rays. But ozone close to the surface doesn't make its way up into the protective layer, Wilson said.

Low-atmosphere ozone levels have dropped over the years. The attainment level was once 120 ppb. When the federal government considered where to place the new ozone standard, some experts called for thresholds as low as 60 ppb before settling on 70 ppb.

McCahan, the attorney for the Environmental Defense Fund, said there are harmful effects as low as 60 ppb.

In reality, experts don't know if there's a level that's totally safe for humans, Wilson said.

"The levels we are breathing in the air are not the best for us," he said.

Follow Steve Hardy on Twitter, @SteveRHardy.