CASPER, Wyo. (AP) — For the first time in about six years, state regulators this week have invoked special conditions that require energy companies to reduce pollution from oil and gas fields in southwest Wyoming.

The Wyoming Department of Environmental Quality issued so-called ozone action days in the Upper Green River Basin for Friday and Saturday. Ground-level ozone is the primary ingredient for smog.

On action days, oil and gas producers take steps such as reducing truck idling and limiting refueling.

Chris Merrill, of the Wyoming Outdoor Council, says the action day is a reminder that ozone levels can still be a threat in Wyoming, and more work needs to be done to control it.