Is Inversion Season Over?

Yes, and no.

If you mean situations in which a shallow, persistent (i.e., multiday) cold pool is capped by a layer in which temperature increases in height, then it's pretty much over.  With no snow on the ground, a higher sun, and a longer day than a few weeks ago, shallow cold pools are now readily burned off during the day.

That being said, we can still have an elevated inversion, as was the case yesterday afternoon.

Source: SPC

Under such conditions, however, pollutants are mixed through a layer that extends through a greater depth of the valley and PM2.5 concentrations don't get as high as they do during shallower cold pool events in winter.  Nevertheless, you will see some smog around, so we're not pollution free.

Does this then mean that elevated PM2.5 days are over for this winter?  Nada.  We are just moving into the time of year when dust storms occur, and I wouldn't be surprised if we saw some events this spring if the dry conditions continue.