(Bloomberg News) Wyoming's southwestern region was found to have an unsafe level of smog-causing ozone for the first time, a designation the U.S. Environmental Protection Agency linked to a boom in oil and gas drilling in the state.

The EPA included the Upper Green River Basin in its list of areas nationwide exceeding a federal ozone limit. Until today, Wyoming was the only state where all counties had met the federal ozone limit.

"The growth in the oil and gas industry, which has been explosive in the last few years, is the place we need to look for answers," Bruce Pendery, staff attorney for the Wyoming Outdoor Council, said in an interview. "This will force the state to take significant steps to clean up the air."

Ozone, a precursor to smog, is caused by emissions from vehicle traffic, industrial activities or projects such as road construction. Gas escaping from wells or pipelines contains volatile organic compounds such as benzene, which also can cause smog. Engines running compressors, drill rigs or pumps also release nitrogen oxides, another source of ozone.

Smog is typically observed in summer and often in heavily populated areas such as Los Angeles, Houston and Baltimore. Nationwide, 46 areas exceed the federal standard of 75 parts per billion, including those three metropolitan areas. In Wyoming, the top smog months have been in January, February and March, when sun and warm air traps emissions near to the ground.

Bush-Era Standards

With the regulation today, the EPA is implementing the standard on ozone levels set by the administration of President George W. Bush in 2008. EPA Administrator Lisa Jackson had proposed lowering the standard to 70 parts per billion, which President Barack Obama turned down in September after a wide-ranging lobbying campaign by industry groups.

If the lower standard had been imposed, a number of other counties would have been included in the list today, according to John Walke, clean-air director for the New York-based Natural Resources Defense Council.

"When politics overrides science, real people are denied the benefits of clean air," Walke said in an interview.

Breathing air with high levels of ozone can reduce lung function and aggravate asthma or other respiratory conditions, according to the EPA.

With the official designation of "non-attainment" for the U.S. ozone standard of less than 75 parts per billion, a state or locality must develop a plan to cut its pollution.

Wyoming officials have established a task force to come up with recommendations to boost air quality, according to Pendery, a member of that task force.