Wood Stoves Soot Seems to Be a Main Actor in the Global Warming

New studies of soot produced by primitive cook stoves used in poor countries from South Asia, Latin America and Africa found it more harmful and with a much greater impact on global climate change than thought.

The soot quantity produced by "biofuels" (wood, agricultural waste and dried manure) seems to be much higher than scientists suspected. Soot particles form aerosols absorb light, increasing temperature in the atmosphere and decreasing it on land. These shifts could change rainfall patterns, bringing floods or intense droughts. This has impact on agriculture-based economies of the same developing countries. "Perhaps as many as 400 million of these stoves, fueled by wood or crop residue, are used daily for cooking and heating by more than 2 billion people worldwide," said Tami Bond, Ph.D., and doctoral candidate Chris Roden of the University of Illinois, Urbana-Champaign.

This team estimated that burning firewood - the main biofuel - produces 800,000 metric tons of soot worldwide each year, compared to 890,000 produced by diesel cars and trucks. "These two sources each account for about 10 % of the soot emitted into the world's atmosphere each year," said Bond.

Field tests in Honduras showed that the traditional stoves produce two times more soot than measured in lab experiments. "These dark, sooty particles, which are darker than those produced by grassland or forest fires, have a climate warming effect because they absorb solar energy and heat the atmosphere," said Roden.

Indian scientists made laboratory tests to see how much soot 11 types of biofuel emit when burnt in traditional one-pot stoves, representing over 80 % of stove use in India. They believe that biofuels contribute to 42 % of India's total soot emissions, open burning (like forest fires) produced 33 % and use of fossil fuels produced 25 %.

Soot could have a negative impact on the atmosphere, particularly given the extensive use of biofuels in India. To diminish the impact on the environment, cleaner fuels - like liquid petroleum gas or kerosene - must be used, but these alternatives are more expensive and less accessible to poor people. "Above all, this not an attempt to blame the developing countries for polluting the world," said Kirk Smith, professor of environmental health sciences at the University of California, Berkeley, US.

"Developed nations are still responsible for the majority of greenhouse gas production. Tackling the problem of burning solid biofuels would be a win-win situation because of the combined health and environmental benefits that would result from reducing soot emissions," says Smith.

Home contamination caused by cooking stoves affects the health of hundreds of millions of people, and killing more children annually than malaria or HIV/AIDS. It is a major cause of respiratory infections, pneumonia, lung cancer, eye infections and tuberculosis. "Emissions from wood cook stoves affect the health of users -- especially of women and children -- neighborhood air quality, and global climate. Reducing these emissions, through the use of cleaner burning stoves and fuels, should have far-reaching benefits," Bond said.

Techniques used in field tests in Honduras included sensors for measuring carbon dioxide and carbon monoxide, particle soot absorption, particle color and concentration. "We expected field measurements to be different from lab measurements, and we suspected the amount of black carbon from these stoves would be higher than open burning, but we were surprised by how much," Roden said.

The problem is increased by the poor quality of the stoves. And the number of people using traditional stoves is increasing, being estimated to 2.6 billion by 2030. "Designing and distributing improved cook stoves may be an effective method of mitigating global climate change, and can improve the health of the users," Roden said.

"However, the cook stoves must be well designed and properly tested. They must be built with local traditions and practices in mind and must be easy to use, or they may become expensive doorstops."