To estimate regional emissions from yak dung burning, we used the average per capita yak dung consumption of approximately 1640 kg/year . This per capita biofuel use is considerably higher than the global average, most likely due to the cold climate and high heating needs.
Combining this per capita yak dung consumption with the 2000 population census data of 4291 residents in Nam Co, approximately 7 kt/year of yak dung is consumed in the region. Coupling this value with emission factors previously reported from different experiments, several estimates of BC and PM2.5 emissions from Nam Co in 2000 can be derived: 1) 0.84 Mg/year BC and 18 Mg/year PM2.5 based on the emission factor of BC and TC as 0.12 and 2.56 g/kg, respectively ; 2) 2.1 Mg/year BC and 160 Mg/year PM2.5 based on 22.9 gC/kg fuel and our average BC/PM2.5 ratio 0.013; and 3) 3.4 Mg/year BC and 31 Mg/ year PM2.5 based on the emission factor of BC and TC as 0.49 and 4.36 g/kg, respectively. Residential BC and PM2.5 emissions in Tibet were estimated to be 0.695 and 3.46 Gg/year in 2000, respectively, without including emissions from yak dung burning. Since Nam Co only holds 0.2% of the rural population in Tibet based on the Tibet Statistical Yearbook 2012 and assuming 0.8e3.4 Mg/year of BC and 18e160 Mg/year of PM2.5 from the residences in Nam Co, it is likely that another 0.4e1.7 Gg/year of additional BC and 9e80 Gg/year of PM2.5 emissions have been unaccounted for in their estimate.