Ozone pollution is generally a problem in the summer, but scientists in Boulder say natural gas production is contributing to a winter ozone problem.
Scientists at the National Oceanic and Atmospheric Administration say the pollutant formed quickly in cold February days around two major gas fields in southwestern Wyoming. That happened when there were temperature inversions and snow cover to reflect sunlight to start the chemical reactions to form ozone.
Ground-level ozone is a key component of smog and is typically associated with hot weather. It forms when the sun bakes pollutants such as vehicle exhaust and vapors from everything from paint.
Colorado regulators have toughened regulations on gas-field emissions to try to reduce the Denver-area's ozone levels.