https://www.vice.com/en_us/article/jgqazy/wildfire-smoke-is-alive

On September 9, 2020, Californians woke up to an apocalyptic orange sky caused by smoke from more than 20 wildfires burning up and down the West Coast. The smoky haze was photographed settling over populated cities like San Francisco, where millions breathed in hazardous air conditions.

Craig Shoemaker, a meteorologist with the National Weather Service in Sacramento, told the New York Times, “Without the smoke, it would be a clear day. This is all generated from the fires.”