The good news is that firefighters in California have regained control of the Caldor Fire near Lake Tahoe and tens of thousands of evacuated residents can now return to their homes. The bad news is the Caldor Fire is the second wildfire this season to burn through the Sierra Nevada Mountains from one side to the other. Something that never happened before this year. The other fire to do it is the Dixie Fire further north, which is on pace to be the largest California wildfire on record. And while thousands have been impacted with evacuations, millions of people in western states have been living with the smoke for weeks. The general guidance when living with hazy and polluted air is to stay indoors. But NPR's Nathan Rott reports on new research that shows the air behind closed doors may not be much better. And NPR's Lauren Sommer reports on a region of the country that is leading the way with fire prevention that may surprise you.