The photo below, taken yesterday afternoon from the Bonneville Shoreline Trail in the Avenues Foothills, showed a very well defined pollution layer extending to perhaps about 6500 or 7000 feet.
The corresponding sounding taken that afternoon showed a shallow surface-based mixed layer that extended to about 850 mb (1597 m; 5240 ft) above which the atmosphere was nearly isothermal (i.e., constant temperature) with height to 775 mb.
PM2.5 concentrations this afternoon reached almost 30 ug/m3, which is in the upper half of the moderate category. Then the dropped abruptly, although that looks awfully spurious to me.
|Source: Utah DAQ|