Below shows one period during which the chopper was flying across the Salt Lake Valley and over portions of the Wasatch Front. The chopper position varies, as well as its altitude, and it is clear that sometimes it it flying in clean air (blues) other times "dirty" air with much higher PM2.5 values (red).
Between about 2100 and 2600 meters, the air is mostly clean. All observations were below about 30 ug/m3 and the vast majority were < 5 ug/m3.
However, go higher up and there are some horrible PM2.5 values again, some as high (or higher) as in the polluted air in the valley. This is what I suspect is the smoke from the California fires. This smoke isn't uniform. There are some pockets of clean air, but the PM2.5 levels are quite high in some locations.
This is simply incredible data. I've never seen anything like it. Wintertime pollution trapped in the valley. Smoke from extreme wildfires at upper levels. Remarkable. Thanks to the MesoWest team and KSL for making this happen. Note that this data is freely available in real time at http://utahaq.chpc.utah.edu/.