Indoor air pollution from burning yak dung as a household fuel in Tibet

- Real-time BC and PM2.5 concentrations were measured in households in Nam Co, Tibet.
- 23 households were surveyed on energy use and awareness of indoor air pollution.
- Chimney installation may not by itself ensure adequate indoor air quality.
- We observed a lower BC/PM2.5 ratio for dung combustion than previous estimates.
- About 0.4-1.7 Gg/year of additional BC is emitted by yak dung combustion in Tibet.

Yak dung is widely used for cooking and heating in Tibet. We measured real-time concentrations of black carbon (BC) and fine particulate matter with an aerodynamic diameter of 2.5 μm or less (PM2.5) emitted by yak dung burning in six households with different living conditions and stove types in the Nam Co region, Tibet. We observed a much lower average BC/PM2.5 mass ratio (0.013, range 0.006-0.028) from dung combustion in this area than previously reported estimates, ranging between 0.05 and 0.11. Based on our measurements, estimated fuel use, and published emission factors of BC and PM2.5, about 0.4-1.7 Gg/year of BC is emitted by yak dung combustion in Tibet in addition to the previously estimated 0.70 Gg/year of BC for Tibetan residential sources. Our survey shows that most residents were aware of adverse health impacts of indoor yak dung combustion and approximately 2/3 of residents had already installed chimney stoves to mitigate indoor air pollution. However, our measurements reveal that, without adequate ventilation, installing a chimney may not ensure good indoor air quality. For instance, the 6-h average BC and PM2.5 concentrations in a stone house using a chimney stove were 24.5 and 873 μg/m3, respectively. We also observed a change in the BC/PM2.5 ratios before and after a snow event. The impact of dung moisture content on combustion efficiency and pollutant emissions needs further investigation.