We're not quite into inversion season yet, but we've reached that time of year where the incoming solar radiation is simply not sufficient to build a deep convective boundary layer in the afternoon. As a result, considerable urban smog (I shouldn't call it haze, but I like Jimi Hendrix too much) is developing over the Salt Lake Valley during quiescent weather periods.
Yesterday afternoon, for example, there was noticeable smog as one looked south toward the Oquirrh Mountains from near Ensign Peak.
In the afternoon sounding from Salt Lake City airport, it appears that the convective boundary layer extends to just below 700 mb (~10,000 ft) which is close to the crest of the surrounding mountains. Thus, we're getting decent mixing, but perhaps not enough to pump everything out. Hence the smog.
The good news is that PM2.5 levels remain relatively low.
|Source: Utah Division of Air Quality|