While many of our Western readers will be grateful right now for the largely fossil fuel-powered central heating that keeps our homes snug and warm in the biting winter months, spare a thought for the nomads of the Himalayas, whose home energy plan consists of a more renewable but somewhat less savory fuel: yak dung. A new study in the journal Atmospheric Environment reports that yak dung – burnt indoors for the dual purpose of cooking and staying warm – fills the air with dangerous black carbon.

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The households in the study mostly used yak dung as fuel for cooking and they all used yak dung as the only fuel for heating.

It was estimated by the World Health Organization (WHO) that 4.3 million people died prematurely around the world in 2012 as a consequence of indoor air pollution from stoves that used coal, wood, dung or crop waste as fuel. In comparison, outdoor air pollution was estimated to be linked to 3.7 million deaths in 2012.

Yaks are central to nomadic society in Tibet. The long-haired, cattle-related creatures work as pack animals and provide meat and milk, as well as fiber for fabrics, and their dung is used as heating fuel.

Although previous studies have examined indoor air quality in Tibet, they had only looked at the summer season. The researchers behind the new study – from the Department of Environmental Sciences at Emory University and the Department of Environmental Health at the Rollins School of Public Health, both in Atlanta, GA – wanted to investigate indoor emissions during the cold winter months.

“Indoor air pollution is a huge human health problem throughout the developing world,” says co-author Eri Saikawa. “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.”

In March 2013, Saikawa’s colleague, Qingyang Xiao – a graduate student at Rollins School of Public Health – traveled to Nam Co in Tibet and measured indoor concentrations of fine particulate matter in six households using battery powered aerosol monitors. The households mostly used yak dung as the main fuel for cooking and they all used yak dung as the only fuel for heating.

Fine particulate matter consists of particles that are 2.5 micrometers in diameter or smaller – mainly black carbon and organic carbon. Xiao found that the average concentrations for black carbon and fine particulate matter were nearly twice as dense as those reported among similar households in India and Mexico.

Four of the homes in the study were traditional tents and two were simple stone houses. In all cases, the homes consisted of one room where all family members slept, ate and cooked. Half of the homes had open stoves without chimneys and half had stoves with chimneys.

The home with the lowest indoor concentrations of fine particulate matter used liquefied petroleum gas for cooking and yak dung for heating. The home with the highest black carbon concentrations was, surprisingly, a stone house with a chimney.

“That was surprising,” Saikawa says. “It shows that it is misleading to think that having a chimney will always improve the situation, unless you can be sure that the home is ventilated correctly and that you have proper air flow within a dwelling.”

In addition to the measurements of indoor emissions, Xiao also surveyed members of 23 households on energy use and awareness of indoor pollution.

She found that the families spent an average of 16 hours per day indoors during the winter months, and 70% of respondents were aware of the health problems concerning indoor pollution. However, not all families had the financial means to invest in a chimney, as the average household income is less than $900 a year and chimneys cost around $60.

The researchers also noted that, after rain or snowfall, piles of uncovered dung are moist and less combustible, which results in more emissions of fine particulate matter caused by smoldering.

Black carbon has the greatest impact at high altitudes – such as in the Himalayas – because it absorbs heat in the atmosphere and reduces the ability to reflect sunlight when it is deposited on snow and ice.

Saikawa explains:

Black carbon emissions from burning biofuel such as yak dung have not been quantified before in the atmosphere of the Himalayas. 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.”

Next, the team will expand on its small sample of households and investigate indoor emissions in other areas of Tibet. The researchers will also link these measurements to a biomarker study involving blood samples of the inhabitants of these households.

“We want to use our data to make the world a better place,” Saikawa says. “The ultimate goal is to reduce pollution from biomass fuels in ways that benefit human health and reduce the climate impact.”