Yeah, that's easy to underestimate. Where I live they've even declared a ban on open fires; a number of people have a fireplace / pit / thing in their back yard which is used for social events, but during certain weather conditions that smoke lingers. And because firewood is expensive people will use whatever they get their hands on. Also, people don't have proper stoves, and people don't know how to make a proper fire, so the result is... a lot of noxious smoke and poor air quality.