dangers of wood burning during an inversion (or in a major City).
The general rule is that one fireplace produces the same pollution as almost 1,000 cars. So yes, a few hundred thousand burning wood can cause significant pollution (especially back in the day when fire places didn't have filters (today's woodburning stoves do a much better job of filtering the pollution)
http://www.grreporter.info/en/fireplace_pollutes_air_much_1000_cars/8814