Normal summer pollution on the Wasatch Front is a regular cycle of ozone rising in the day and falling at night because the sun kicks off the chemical reaction that forms the pollutant. That allows for safe air in the morning and at night for outdoor activities.
READ: Utah's double-whammy air quality concerns doctor
Wildfires create particulates (smoke) that linger no matter the time of day.
Here's a look at how the highest rolling 24-hour average of smoke in the last two days compares with the worst days of December, January and February, when winter inversions trap particulates.
