Imagine that you drive north from Montrose, Colorado to Grand Junction. Air quality starts out pretty good, gets worse. You take I-70 east to Glenwood Springs, then angle southeast, but higher, to Aspen. It looks like the smoke and ash of regional fires flow up both Colorado and Roaring Fork rivers. Upvalley. I felt it in my lungs which is what got me interested. Here's the key to my slapped together chart. 0 to 50 = Good 51 to 100 = Moderate 101 to 150 = Unhealthy for sensitive groups 151 to 200 = Unhealthy 201 to 300 = Very unhealthy 301+ = Hazardous I suspect this random bit of citizen science (data points from public resources) is no more than that. But wildfires move fast and fire isn't the only concern.