Yak dung burning in Tibetan households pollutes indoor air

Burning of yak dung can fill the indoor air with dangerous levels of fine particulate matter, including black carbon, a new study on Tibetan households has warned.
During the long cold season, traditional nomadic people in Tibet spend much of their time in dwellings where they cook and stay warm by burning yak dung.
This can fill their indoor air with dangerous levels of fine particulate matter, researchers have found.
"Indoor air pollution is a huge human health problem throughout the developing world," said Eri Saikawa, an assistant professor in the Department of Environmental Sciences at Emory University and in the Department of Environmental Health at the Rollins School of Public Health.

"In a cold region like Tibet, the impact on individuals could be even greater because they spend so much time indoors and try to keep their homes as air tight as possible," Saikawa said.
In March 2013, Qingyang Xiao, a graduate student in Rollins School of Public Health, travelled to the Tibetan region of Nam Co to gather data. About 4,500 residents live in the region, at an altitude of 4,730 metres.

Xiao used battery powered aerosol monitors to measure indoor concentrations of fine particulate matter, or particles 2.5 micrometres in diameter or smaller, which consists mainly of black carbon and organic carbon.

She recorded the measurements in six households with different living conditions and stove types. Yak dung was the main fuel for cooking and the only fuel for heating.
The results showed that the average concentrations for black carbon and fine particulate matter were nearly double those reported by some similar studies of households in areas of lower altitude and warmer climates, such as India and Mexico.
The moisture content of the yak dung is a key factor in the emission levels, Saikawa said.
After a rain or snowfall, the piles of uncovered dung are moist, leading to incomplete combustion and more emissions of fine particulate matter due to increased organic carbon by smoldering.

Saikawa is also studying levels of black carbon emissions in the outdoor environment generated by the burning of biomass fuels like yak dung.
Black carbon absorbs heat in the atmosphere and reduces the ability to reflect sunlight when deposited on snow and ice. Its impact is greatest at high altitudes.
"Black carbon emissions from burning biofuel such as yak dung have not been quantified before in the atmosphere of the Himalayas," Saikawa said.
"We know that many Himalayan glaciers are melting rapidly, and our work suggests that more black carbon is getting deposited on them than previously thought," Saikawa said.

The study was published in the journal Atmospheric Environment.