Smoke from forest fires returned to Tooele Valley this weekend, lowering air quality to the yellow or moderate level, according to the Utah Division Of Air Quality.
The DAQ reported yellow air quality in Tooele County from Friday through Monday with continued yellow air quality forecast to continue through Wednesday.
A National Weather Service forecast map shows smoke moving into northern Utah from California.
The haze is expected to start clearing Wednesday night with Thursday forecast as clear in Tooele County, according to the NWS.
Wildfire smoke is composed of a complex mixture of gases, fine particles, and water vapor that form when organic matter burns. Particulates from smoke are a mixture of solid particles — pieces of wood and other burning solids — and liquid droplets.
The biggest health threat from wildfire smoke comes from fine particles, according to the Utah Department of Environmental Quality.
During yellow, or moderate, air quality periods the DAQ lists activity as unrestricted, but unusually sensitive people should consider reducing prolonged or heavy outdoor exertion, according to the DAQ.
If smoke gets thick, the DAQ advises people with existing heart or respiratory ailments to reduce exertion and outdoor activity.