It happens. Citrus growers often used smudge pots in the winter to protect their crops. Average low in Upland is 42 in Dec and 43 in Jan.
Yeah, I’ve seen a lot of info about Florida citrus farmers doing the same thing. But the only places I see on the NWS forecast synopses that may get below 40 are well outside any area that could be impacted by an air quality issue.