It wasn't much of a race. Before the dog days of summer arrived, air monitors in Denton and northern Tarrant counties had already racked up records of excessive ozone.
The Keller monitor logged its fourth day above a federal limit on Wednesday. Denton's monitor logged its fourth on Thursday.
It's been five years since ozone violations occurred so quickly in the Dallas-Fort Worth region. In the summer of 2006, ozone levels at several monitors exceeded 100 parts per billion in early June, according to state records.
Ground-level ozone, formed as engine exhaust and other pollutants react with sunlight, can aggravate asthma and cause permanent lung damage, according to the Environmental Protection Agency.
In order to promote improvement in the region's air quality, an old federal standard allows no more than three days each year with an eight-hour average of 85 parts per billion at any one monitor. The EPA has known the standard does not protect public health in the long term and plans to announce a new, stricter criterion soon, agency officials have said.
Yet, ozone levels in Denton have exceeded the old federal limit earlier each year over the past three summers, state records show.
"Ozone season" spans from March 1 to Oct. 31, said Joe Hubbard, spokesman for Region 6 of the EPA, so it is too soon to tell whether this year's preliminary readings mean that the state's latest plan to comply with the Clean Air Act has failed.
That deadline is June 15, 2013.
Denton Mayor Mark Burroughs, chairman of the North Texas Clean Air Steering Committee, said the high ozone readings don't bode well for the region, either now or when the stricter standards are announced.
"The plan was based on past control strategies that had worked, and were working, for the region," Burroughs said. "But is it enough? We don't know. If this summer is an indication, we might still be in trouble."
Weather conditions can play a significant role in ozone formation, according to Terry Clawson, spokesman for the Texas Commission on Environmental Quality. However, regulatory levels of ozone are averaged over three years to account for that, Clawson wrote in an e-mail.
"Even though there are always variations in meteorology that impact ozone levels, we think that D-FW ozone will continue the longer-term downward trend despite a significant population increase," Clawson wrote.
To address the problem, TCEQ officials will hear public comments on a revised plan to improve the region's air quality at 10 a.m. and 6:30 p.m. Thursday at Arlington City Hall.
The plan includes some new emission-control measures, Clawson said.
In addition, state officials ordered a field study of the area by atmospheric scientists from Rice University and the University of Texas.
David T. Allen, a chemical engineering professor at UT, said the effort is similar to a field study the group conducted along the Texas Gulf Coast. Corrective actions taken by state regulators since then have greatly improved air quality there, he said.
The group gathered data from the end of May through June and has finished that phase of the study. Some of the measurements were taken in airplanes, so that the scientists could determine how ozone formation might be traveling in the area. Some of the measurements were taken continuously on the ground in various locations, including side-by-side air monitors.
Other measurements were taken in a laboratory. One air sample was "quenched," or frozen, to suspend molecular action; the other is "cooked" to simulate field conditions. Then the team can determine how much ozone is formed locally, Allen said.
"The study was designed to answer two questions: how much ozone is formed locally and how much gets blown in from other areas," he said.
The group has begun analyzing the results, Allen said.
Local environmental groups have long been critical of what they say is lax state regulation of industrial polluters and say they're increasingly concerned about emissions, particularly volatile organic compounds (VOCs) from natural gas production facilities.
While such facilities are known to emit VOCs, a component of ozone formation, compressors and other combustion equipment in natural gas fields can also emit nitrogen oxides, a primary component of ozone formation, according to Christine Wiedinmyer, an atmospheric chemist at the National Center for Atmospheric Research in Boulder, Colo.
Allen said the research team is doing the best it can to find out the underlying causes of the persistent ozone in the area.
"It's better to have good information, no matter how we use it," Allen said.
Burroughs encourages residents to take voluntary steps to help reduce ozone - mowing late in the day and limiting car trips - which might help avoid mandatory future measures that are likely to be more painful.
"It might help to think of it as a summer thing," Burroughs said, adding that it isn't just about the federal rules, but people's health, too.
"More and more kids have to have inhalers," Burroughs said. "And more elderly people have upper respiratory infections in the middle of summer."
PEGGY HEINKEL-WOLFE can be reached at 940-566-6881. Her e-mail address is pheinkel-wolfe@dentonrc.com.
Oh, The Ozone
State ozone monitors in Denton and northern Tarrant counties have recorded persistent ozone levels above federal standards over the past five years, even as ozone levels - measured as an eight-hour average each day - have dropped elsewhere in the Dallas-Fort Worth area. Here are the four highest ozone levels recorded so far this year at those monitors (as of Thursday, and in parts per billion).
Denton Airport South
June 6 - 95
June 22 - 90
July 5 - 95
July 7 - 85
Keller
June 6 - 90
June 22 - 92
July 6 - 92
July 7 - 90
Grapevine Fairway
June 6 - 91
July 5 - 88
July 7 - 83
July 6 - 82
