This week the pattern has produced some stagnant air conditions. Near the coast the lighter winds have allowed marine layer to form up in the night and morning and to only slowly and partially clear. The same mechanism also traps the wildfire smoke haze near the surface. Add to that high clouds from a former tropical system and there was a lot of sun filtering today.
This combination looks to hang around til later Friday morning, the cold front looks to pass thru Friday afternoon and the strong NW winds will mix out the marine layer and weaken the temperature inversion capping in all the smoke haze as well. The pace of the NW winds (15-25mph Friday afternoon) will also likely thin the smoke concentrations locally. The air quality alert in SLO county was extended into Friday morning but I think the hidden good news in that is that it was not extended further.
The weekend breeze will still be around and temps will drop and any night and morning marine clouds will be much more imited and clear faster where it does form. Early next week looks mild before a ridge in the upper atmosphere moves in again to boost temps but not to extreme levels.