In Southeast Missouri, it has delivered relief to everyone who is watching ozone levels, from business leaders to environmentalists.
Southeast Missouri, with ozone monitors in Perry and Ste. Genevieve counties, for several years has battled against air-quality issues and fought to keep ozone readings at allowed levels to avoid being designated a "nonattainment area" by the Environmental Protection Agency. Such a designation would lead to strict and costly regulations.
Not once this summer has the ozone level exceeded the EPA's desired standards. The most recent reading at the monitoring station near Farrar, Mo., was about 65 parts per billion -- well below the EPA's 2008 National Ambient Air Quality Standard of 75 parts per billion.
David Grimes, regional planner with the Southeast Missouri Regional Planning and Economic Development Commission, said ozone is created when nitrogen oxide and volatile organic compounds, emitted by industries and vehicles, combine on hot and sunny days. In the absence of strong heat, or even if there's a cool breeze, conditions are less optimal for the formation of ozone.
Grimes said the cool weather "absolutely is" a help.
July is normally considered the height of the EPA's declared ozone season, which begins April 1 and ends Oct. 31. According to data from the Weather Channel, July is typically the warmest month in Missouri, with an average temperature of 89 degrees.
This year, however, the weather has been almost springlike, with temperatures dipping to the 50s some evenings.
The EPA chose to maintain its part-per-billion standard in 2011, although it considered lowering it to 60 or 70 parts per billion. The agency decided to revisit an adjustment of the standard in 2013. Grimes said no new standard has been released and no new reviews performed, which he said is a good thing for the region.
He said the EPA has requested the Clean Air Science Advisory Committee schedule a formal meeting for 2014 to review standards. That meeting is required before any changes can occur.
"They released a statement in March 2008 and should have released one in March 2013, but it's looking like it won't be released until about 2015, which is good for us," Grimes said. "We had a bad year last year ... but this year we would be compliant. If this pattern continues next year, we would be comfortably compliant."
Even if Perry County maintains an average below the EPA standard, the area still could face consequences. The St. Louis district includes multiple counties, including Jefferson, which connects the St. Louis site and the Ste. Genevieve site. Grimes said St. Louis is out of compliance and most likely will be designated a nonattainment area. If that happens, neighboring areas fall under suspicion because of their possible contribution to high ozone readings. Grimes said "it's like dominoes."
"Ste. Genevieve could be classified a nonattainment area because it's near the St. Louis district," he said. "Same with Perry County; we could be considered if Ste. Genevieve became a nonattainment area. And if Perry County were to be designated as nonattainment, then Cape County would be looked at."
Grimes said there have been no "exceedences" this year in Perry County or neighboring Ste. Genevieve County, but he's trying to be realistic. He expects temperatures eventually will rise, which could lead to rising ozone levels.
For now, Grimes said he is encouraging residents to do little things to keep emissions low, such as carpooling, mowing lawns in the evening and "stopping at the click" rather than topping off while refueling their vehicles as gas stations.