Several reasons potentially explain this. Ventilation of houses could be somewhat limited if residents close windows and doors to stay warm and save fuel.We estimated the air exchange rate in the different households (Table 2). In tents that use simple stoves and have a hole on top, the PM2.5 concentrations dropped the fastest (14.0 mg/m3/min) after the fire was extinguished among all the households. In contrast, the PM2.5 exchange rate in the simple house (ID 6 in Table 2) at night when the door was closed was the lowest in this study (1.56 mg/m3/min). This low exchange rate does not reflect the ventilation of this household during daytime when the doorwas open, but it provides an indication that the ventilation of the stone house may have been similarly limited. Maintaining ventilation even with a chimney is important because the chimney cannot ventilate emissions introduced to the living area when, for example, fuel is added or lighting the stove. Our survey showed that a larger percentage of households using chimney stoves (75%) were not worried about their health after installing a chimney (Fig. 3, right), but our data show that installing a chimney may not be a sufficient mitigation measure in a house. Residents living in one house with a chimney were still exposed to severe indoor air
pollution.