When the Dallas County Medical Society asked Texas environmental regulators in October to increase pollution controls on coal-fired power plants, they knew it would be a tough sell.But the association of more than 6,500 physicians said it was fed up with seeing patients suffering from the region’s air quality problems, which are among the worst in the nation. And members said real improvement was possible by targeting two of the nation’s oldest coal-fired plants, which are among the state’s biggest sources of nitrogen oxide emissions — air pollutants that react with other toxic chemicals in the presence of sunlight to create ozone.Still, the association’s members were not prepared for what happened when the Texas Commission on Environmental Quality took up their request.“There is data that shows that we should be raising the ozone levels,” Bryan Shaw, the commission’s chairman, said to doctors who testified. "And I am not at all suggesting that’s true. I'm suggesting that there is data that shows that we’re at a point where there's noise there, and I think that there’s concern that we may be chasing the wrong rabbit, as I sometimes utilize, to try to capture that.”Later in the meeting, he added, “It does no one any good to go and require reducing ozone if we’re not having a beneficial impact.” “It was completely unexpected,” said Robert Haley, an epidemiologist and professor at the University of Texas Southwestern Medical Center who attended the meeting. “In the scientific world, nobody questions this. All of this was argued decades ago.”The commission denied the medical society’s petition, following the recommendation of its staff.Doctors and scientists statewide believe that Dallas-Fort Worth’s ozone levels are a major public health concern. High levels of ozone are particularly risky for people with asthma, lung disease, heart disease and even diabetes — health problems that afflict more than 1.5 million North Texans out of a population of roughly 7 million.Dallas-Fort Worth ozone levels have long been well above federal standards set to protect health, and scientists are pushing for those standards to be lower.But some of them fear that Texas officials and politicians are too focused on bolstering the state’s explosive economic growth and energy boom to deal comprehensively with the problem.“It’s very political, a lot of economic issues involved,” Haley said.In public statements, Shaw has argued that requiring expensive pollution controls in coal-fired plants could have an “economic ripple” effect, driving up the price of power and disproportionately affecting poor Texans. And state officials say Texas’ air quality has improved significantly since 2000 despite a huge population increase, as nitrogen oxide emissions decreased by more than 50 percent. While that trend has been mirrored nationwide — in large part because of new vehicle pollution standards imposed by the federal government — Texas’ investments in cleaner energy sources and vehicle replacement programs have also played a role, officials say.But the steady downward march that ozone levels began in North Texas in 2000 stopped in 2007.The state environmental agency says it is committed to reducing ozone. Still, in recent years its work has not translated into comprehensive policies or solutions, scientists and advocates say.“The TCEQ staff has done some of the best modeling and sponsored some of the best science in the country, trying to inform their efforts to reduce ozone,” said Daniel Cohan, a professor at Rice University. But he added that “sometimes you can have a paralysis by analysis. … The modeling has been excellent, but a plan has yet to emerge.”When the agency’s commissioners voted against more restrictions on coal plant emissions in October, they said the change would be premature because the agency is already working on a federally required plan to reduce ozone in Dallas-Fort Worth. But in each of the five related plans it has developed since 1991, the agency has predicted that the region would meet federal ozone limits within one to five years — and it has always been wrong.In the 2011 plan, the agency’s staff said new federal gasoline standards alone would help ozone drop from more than 85 parts per billion to 78 in just two years (the current standard is 75 parts per billion), and staffers rejected dozens of other strategies suggested to improve air quality, such as reducing emissions from cement kilns and coal plants. Levels still hover around 87 parts per billion.David Brymer, director of the commission’s office of air, said the agency’s models have improved significantly. And he said the region’s ozone level is calculated over a three-year period, so the current one includes the unusually hot year of 2011.“That year has kind of skewed us a little bit,” Brymer said. Looking at more recent data, he argues, “it becomes a lot more clear that we’re not really that far off as what it might seem.”The agency now says it believes that new federal gasoline standards and the increase in newer, more efficient vehicles will allow ozone levels to drop to just over 75 parts per billion by 2018.