The searing summer in St. Louis has helped drive ozone levels to the highest levels seen in five years, killing the region's chances for meeting federal standards any time soon.

Data from air monitors across the region quantify the extent of the problem. From April 1 through the end of August, the 11 ozone monitors recorded 172 instances in which concentrations exceeded federal standards. And there’s still almost two months remaining before the ozone season ends on Oct. 31. Ground-level ozone, a colorless gas, can trigger asthma attacks and aggravate other respiratory ailments.

"We are continuing to have one of the worst ozone seasons in recent years,” Wendy Vit, air quality planning section chief for the Missouri Department of Natural Resources, told members of the state’s Air Conservation Commission during a meeting in Jefferson City last week.

Vit said 12 of 23 ozone monitors across Missouri likely violate the federal 2008 ozone standard of 75 parts per billion measured over an eight-hour period. The state won’t know for sure until the Environmental Protection Agency verifies the data. It also appears that the West Alton monitor in St. Charles County recorded levels that violate the previous federal standard of 80 parts per billion established in 1997.

The entire St. Louis area is out of compliance with the 2008 ozone standard, and the Missouri portion of the region still doesn't comply with the previous standard. The so-called non-attainment classifications require the states to develop strategies for controlling ozone or risk consequences that include the loss of highway funding.

Those air pollution control plans -- which include requirements for auto emissions tests every two years and the use of reformulated gasoline -- have been working, air planning officials and regulators say.

In fact, by last fall, ozone levels in St. Louis were low enough that the state of Missouri sought to have its half of the metro area declared in compliance with the 1997 standard. But this summer’s ozone levels have dashed those plans. 

"That is now essentially a moot point," Vit told the Air Commission. "We cannot move forward. ... Essentially, St. Louis will be out of compliance with the old standard as well as the current 2008 standard, and it just complicates ozone planning, to say the least, in St. Louis."

By late Wednesday, DNR spokeswoman Renee Bungart had not responded to written questions submitted Tuesday morning.

Mike Jay, an environmental scientist at the EPA’s regional office in Kansas City, said its unclear what the consequences of continued noncompliance will be for Missouri.

Unlike pollutants emitted directly by smokestacks and tailpipes, ozone is formed by a chemical reaction of nitrogen oxides and volatile organic compounds that "cook" in the sunlight. The pollutants originate from power plants, factories, automobiles and gasoline vapors among other sources.

Because of the role of sunlight and heat in the formation of ground-level ozone, it’s no surprise the St. Louis area and other Midwest cities have experienced air quality problems this summer, which will end up among the hottest and driest on record.

But the reasons for high ozone readings are more complex, said Jay Turner, an air quality expert and associate engineering professor at Washington University.

In fact, drivers for high ozone readings can vary from day to day, Turner said. While he hasn't thoroughly analyzed this summer's data, he said an increase in regional power plant emissions related to the heat could also have contributed. And the lack of afternoon rain showers, typical in most years, probably played a part.

Regular rains can "shave the peak off those eight-hour ozone averages," he said. "That hasn’t been happening."

And because ozone pollution, and pollutants that trigger its formation, can travel hundreds of miles, problems can originate several states away.

That’s what happened on June 8 and 9, for instance, when an upper level air mass, driven by high pressure system over Lake Michigan, was driven into St. Louis, bringing with it high ozone levels that showed up first on rural air monitors in Illinois.

"Historically, that’s always when we have our worst ozone, because lots of emissions and lots of ozone are blown into the area from out of state," Turner said.

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