“The hot weather, egged on by a high-pressure system, is helping to mix up a nasty blanket of ground-level ozone that not only looks unappealing but is bad for the lungs.
The Utah Division of Air Quality is classifying Monday and Tuesday air quality conditions on a mandatory action alert level in the Salt Lake area, meaning motorists should refrain from driving as much as possible, and sensitive populations — like those with respiratory conditions — should stay indoors.”

http://www.deseretnews.com/article/865688080/Heat-poor-air-quality-expected-to-linger-this-week.html