While ozone levels are falling in north metro Denver, both sides of the oil-and-gas development debate are taking a deep breath to explain why.

State regulators report that emissions of volatile organic compounds, a key ingredient in ground-level ozone, have fallen by one-half in metro Denver and the northern Front Range, the battlefield over fracking.

The Colorado Oil and Gas Association, an industry group, reports that meanwhile production statewide quadrupled during the six-year period.

The industry, its association said, has reduced emissions and mitigated effects “as part of its ongoing commitment to being good stewards of our natural resources and protecting the environment.”

The falling numbers prove regulations are working and more can be done, said Dan Grossman, the Environmental Defense Fund’s Rocky Mountain regional director and senior director of EDF’s state programs on oil and gas.

“Colorado’s oil and gas industry is responsible for the emission of hundreds of thousands of tons of ozone-precursor VOCs and climate-disrupting methane each year,” he told Colorado Politics. “And as the state looks to comply with the more stringent 2015 ozone standard of 70 ppb, and to continue to reduce greenhouse gas emissions, we can’t afford to rest on our laurels.

Grossman added, “Simple, cost-effective measures (such as increased inspection requirements for smaller wells and replacing leaky pneumatic devices with more efficient ones) are readily available to industry to further reduce pollution from the state’s oil and gas facilities. It is past time to implement them.”

Dan Haley, president and CEO of the Colorado Oil and Gas Association, said the reductions can be attributed to “technological innovation, regulatory initiatives currently on the books and leadership from our industry.”

COGA pointed out that the West’s “background” ozone levels, those that occur naturally without a human-related cause, are the highest in the United States.

“Consequently, addressing ozone related challenges in Colorado is an extremely difficult, economy-wide undertaking, as only 20 to 30 percent of the emissions needed to form ozone in the non-attainment area are actually produced by Colorado-based human activity,” COGA said in a statement. “These activities include but are not limited to cars, boats, planes, tractors, as well as industrial plants, lawn and garden equipment, and even household products like paints, solvents, and hair spray.”

The announcement was part of the industry’s “Clear the Air: The Facts on CEO” campaign. The CEO stands for climate, energy and ozone.

The industry has invested heavily in research and public outreach to convince Coloradans not to impose new rules that could drive the business out of the state.

“This summer’s ozone season is not over yet, and there is a lot Coloradans can do to mitigate ground-level ozone and reduce the number of ozone-exceedance days,” Haley said in a satement. “COGA will continue sharing the facts and working with members of industry to support ongoing efforts to reduce emissions in the nonattainment area.”