One of the main takeaways is the fact that the EPA recommends that, to avoid adverse health effects, daily average PM2.5 concentrations remain below 30ug/m^3 (micrograms per meter cubed).
Here's a figure (from the Department of Air Quality) of Salt Lake County PM2.5 concentrations over the last several days. Notice the fact that the blue line remains above fifty for significant time periods.
Their app is quite handy as well, showing a quick snap shot of current conditions, as well as time-series and air quality forecasts. While air quality has improved over the last 12 hours, we've seen several instantaneous readings of PM2.5 well above 60um/m3, which level is unhealthy for the entire population and not just sensitive groups. Current snapshot as of 10:05PM:
And here are the thresholds:
With the main takeaway being that PM2.5 values above 35 are unhealthy for sensitive groups (kids, those with respiratory ailments, and the elderly) while values above 55 area unhealthy for everyone.