Smoke from fires has been linked to asthma attacks and heart problems and has contributed to a decline in air quality
Last modified on Thu 2 Aug 2018 12.57 BST
As climate change helps push up the number of wildfires in the western US, communities face losing lives and properties to the flames. But another threat also looms large – dangerous exposure to wildfire smoke.
Huge wildfires in California have killed at least six people and razed hundreds of homes. A pall of smoke has shrouded much of California and has wafted eastwards, with Nasa satellites showing fingers of smoke billowing as far as Salt Lake City, Utah.
Much of the smoke from the two fires – near the city of Redding and another close to Yosemite national park – has remained close to ground level, prompting air quality warnings.