The Obama administration's proposal to tighten federal health standards for ground-level ozone could have consequences for oil and gas drillers in the Interior West, where production has boomed over the last decade. Photo courtesy of the National Energy Technology Laboratory.

More than a dozen Western counties with high levels of oil and gas drilling could face tougher requirements for ozone pollution under new proposed federal standards rolled out last week, adding another dose of regulatory uncertainty to an industry already facing tougher scrutiny over its air emissions.

The revised health standard, if finalized later this year, could cause petroleum-rich sections of Colorado, Wyoming, New Mexico and Utah to become so-called "nonattainment areas" for ozone, forcing state governments to revise or adopt new federally approved plans to reduce ozone precursor pollutants in the affected counties.

The two main ozone-forming gases -- nitrogen oxides (NOx) and volatile organic compounds (VOCs) -- are produced from the burning of fossil fuels, but they are also released in abundance by oil and gas drill rigs -- primarily from pump compressors, leaky valves and condensate tanks.

And while industry has taken aggressive steps in recent years to reduce ozone-forming emissions -- including installing pollution controls on compressors and wellheads -- regulators say such efforts may not be enough. Go to story #1