There's this law/regulation, from link Rob posted above.
"In California, those rules are enforced by CARB, the state’s mighty air resources board, and its local affiliates. “I’ve talked to many prescribed fire managers, particularly in the Sierra Nevada over the years, who’ve told me, ‘Yeah, we’ve spent thousands and thousands of dollars to get all geared up to do a prescribed burn,’ and then they get shut down.” Maybe there’s too much smog that day from agricultural emissions in the Central Valley, or even too many locals complain that they don’t like smoke. Reforms after the epic 2017 and 2018 fire seasons led to some loosening of the CARB/prescribed fire rules, but we still have a long way to go. "