You'd be surprised how common it is, the largest source of air pollution in the winter in the SF bay area is from people burning wood.
There's no coal consumption to speak of. There's diesel fuel consumption, though that is largely concentrated on transport corridors (I-80, I-580, US-101).
Wildfire emissions all but certainly swamp woodstove usage.
That said, yes, a small number of poorly-tuned fireplaces can create a large amount of smoke. Where the intent is actual useful heating, and not fireplace-as-decoration, thats' a solvable problem.
Look on page 7
39% Wood Smoke 12 Cooking 12 Other Mobile Sources 12 Road Dust 7 On-Road Motor Vehicles 6 Combustion: Stationary Sources 5 Industrial/Commercial Processes 3 Construction and Farming Dust 2 Animal Waste 1 Wind-Blown Dust 1 Wildfires
Wildfires are basically non-existent in the winter, although the Colorado fire currently doesn't bode well for future California winters.
My understanding is that here in NYC the single largest (non-industrial?) source of air pollution is heating oil. The city banned the two worst heating oils back in 2015, but with a long phase-out period[1]. I would have expected the situation to be the same in most other cities, although SF's weather certainly doesn't justify oil burning the way NYC's does :-)
[1]: https://www.ny-engineers.com/blog/how-nyc-is-phasing-out-hea...