Personal PM2.5 and indoor CO in nomadic tents using open and chimney biomass stoves on the Tibetan Plateau

Abstract

Yak dung is the primary source of energy for cooking and heating of nomadic Tibetan herders. Personal PM2.5 and indoor CO concentrations and time-activity patterns were investigated in nomadic tents with open stoves and locally available chimney stoves. Personal PM2.5 monitoring using a light-scattering datalogger was performed with women in five tents with open fires and four with chimney stoves over 3 days. Meanwhile, indoor CO variation was also measured. Results showed that 24 h average concentrations of PM2.5 and CO in the tents with open stoves were 1.42 mg m−3 (n = 5, SD = 3.26) and 6.69 mg m−3 (n = 4; SD = 9.11), respectively, which were significantly higher than the tents with chimney stoves having 0.14 mg m−3 (n = 4; SD = 0.65) and 0.12 mg m−3 (n = 4; SD = 1.01) of PM2.5 and CO, respectively. Although chimney stoves significantly reduced indoor air pollution, the concentration of PM2.5 was still higher than annual WHO Air Quality Guideline (0.035 mg m−3). Diurnal variability of PM2.5 and CO was similar and had multiple peaks. This phenomenon was closely connected with behaviors of the participants within the tents. Average 1-h peak concentrations of PM2.5 and CO exceed 24-h mean values by a factor of 5.0 and 4.3, respectively. Significant correlation between hourly PM2.5 and CO concentrations was revealed. Generally, women and children spent 7 h longer than other family members within the tent each day and were thus exposed to higher levels of pollutants. Secondhand tobacco smoke and burning of yak oil lamps are also present in many households, but are much smaller contributors to the exposures. Therefore, yak dung combustion contributes substantially to the personal exposure of householders in this setting even during the warmest time of year in this setting and that although exposures are greatly reduced with chimney stoves; they are still high by comparison to national standards or WHO guidelines.