Developing World Antes Up In Greenhouse Game
Science a Gogo October 25, 2006

A jury-rigged smoke sampling system put together by two researchers from the University of Illinois, Urbana-Champaign, has revealed that the primitive cooking stoves used in the developing world may be much bigger contributors to the greenhouse effect than previously thought.

In the past, laboratory tests have been used to measure the pollutants from cooking fires because field tests have been difficult to conduct. But researchers Tami Bond and Chris Roden decided to get a more accurate measure by knocking together a portable battery-operated sampling cart, which included sensors for measuring carbon dioxide and carbon monoxide, particle soot absorption, particle color and concentration. They then took the cart to Honduras where more than 80 percent of families cook their meals over open wood fires.

Reporting the results in the journal Environmental Science & Technology, the researchers said that the stoves in Honduras produced double the expected amount of smoke particles. "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.

Previous estimates of sooty particles from burning firewood were put at around 800,000 metric tons of soot worldwide a year. That figure may now need to be doubled. Put into perspective, diesel cars and trucks generate about 900,000 metric tons of soot annually. In total, from all sources, about 8,000,000 tons of soot is emitted into the world's atmosphere each year.

It's estimated that as many as 400 million cooking stoves - fueled by wood or crop residue - are in use daily worldwide. The sooty particles they produce are darker than those from grassland or forest fires and have a climate warming effect because they absorb solar energy and heat the atmosphere. As well as their effect on the climate, Roden said that smoke from cook stove fires is a major cause of respiratory problems, 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 added.

Roden agreed, but said that any new 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."

Source: American Chemical Society
Photo courtesy of Chris Roden

Article:
Emission Factors and Real-Time Optical Properties of Particles Emitted from Traditional Wood Burning Cookstoves
Christoph A. Roden, Tami C. Bond, Stuart Conway, and Anibal Benjamin Osorto Pinel
Environ. Sci. Technol.; 2006; ASAP Web Release Date: 27-Sep-2006;

Abstract:

It is estimated that the combustion of biofuel generates 20% of all carbonaceous aerosols, yet these particles are studied less than those of other common sources. We designed and built a portable battery-operated emission-sampling cart to measure the real-time optical properties and other emission characteristics of biofuel cookstoves. In a field study in Honduras, we measured emission factors averaging 8.5 g/kg, higher than those found in previous laboratory studies. Strong flaming events emitted very dark particles with the optical properties of black particles. The elemental carbon to total carbon ratios ranged from 0.07 to 0.64, confirming that high elemental carbon fractions can be emitted from biofuel combustion and may not be used to distinguish fossil-fuel from biofuel sources when cooking is the dominant usage. Absorption Ångström exponents, representing the dependence of absorption on wavelength, ranged from 1 (black) to 5 (yellow). Strongly absorbing particles with absorption inversely dependent on wavelength were emitted separately from particles with weak absorption and strong wavelength dependence; the latter probably contained conjugated aromatic compounds. Because combustion occurs in distinct phases, different types of carbonaceous aerosols from biofuel combustion are externally mixed at emission and may have different atmospheric fates. Air Force 1