An ozone health watch for the Valley has been extended into Friday by the Arizona Department of Environmental Quality.
People with existing respiratory conditions should limit time outdoors, especially in the late afternoon when ozone production is at its peak.
Near-unhealthy ozone levels were reported Wednesday and Thursday. Ozone is an invisible gas that is created when other pollutants in the air are heated by the sun.
An absence of cloud cover, a mostly light wind regime, and afternoon high temperatures near 100 degrees by Friday make for optimal local ozone production and accumulation conditions. For these reasons, the existing ozone health watch has been extended once again. It was originally extended from Wednesday to Thursday.