The Idaho Department of Environmental Quality has extended its air quality advisory and banned all outdoor burning across a wide stretch of the state. What the Very Unhealthy Category Actually MeansThe Air Quality Index runs from zero to 500 and is divided into six tiers. Smoke from wildfires in central and eastern Oregon moved into southwest Idaho, pushing air quality in the Boise Treasure Valley into the very unhealthy category. Idaho DEQ extended an air quality advisory and banned outdoor burning across a large portion of the state. Idaho DEQ's website and the free AIR Idaho app provide current readings, three-day forecasts, and advisories.