Mayan families in Guatemala use indoor fires not only for cooking, but also to keep women and newborn babies warm, said Lisa Thompson, an assistant professor in the nursing school at the University of California-San Francisco. Wood-fired post-partum saunas expose women to carbon monoxide levels as high as 300 parts per million for half an hour at a time, and babies for about 10 minutes – well above the U.S. Environmental Protection Agency’s maximum limit of 35 ppm in a 1-hour period, she said.
Low-weight babies and stillbirths also are linked to the indoor air pollution from solid fuel. In Guatemala, babies were born on average 85 grams heavier if their mothers cooked using electricity or gas instead of cookstoves, according to one study.
Less is known about other hazards. When Smith saw people tossing plastic bags into their cooking fires, he began testing for other toxics and found dioxins, which are carcinogens. Even when people do not burn plastic, he said, incomplete combustion produces toxic substances in many “improved” cookstoves.
“There are thousands of things in wood smoke,” he said. “You get significant emissions of benzene, formaldehyde and butadiene. Do you need to say anything more than that 40 percent of the world’s children are in kitchens where there are significant amounts of three major carcinogens? If you had those three pollutants being pumped into kitchens in this country at the levels that it happens, even with no particles, you’d have the National Guard out.”
Some research also suggests soot accounts for 30 percent of the recent warming in the Arctic, and the UN’s Global Alliance for Clean Cookstoves reports that a quarter of global soot emissions can be traced back to cookstoves.
Because methane, carbon monoxide and black carbon remain in the atmosphere for a shorter time, some scientists and policymakers consider them “low-hanging fruit.” Reducing them with better technology could have an immediate impact on climate change.
Such efforts, however, could be problematic.
Families in Bangladesh would rather spend a hypothetical subsidy on health care, education, electricity or other needs than on low-emission stoves, according to one study. Even a half-price discount did little to increase demand for stoves.
In Lima Bautista’s community, the Peruvian government encourages women to “improve” their open-hearth cookstoves as part of a program that gives families a cash incentive to keep their children in school and take them for health checkups.
But with no technical advice available, many families simply raise the hearth or install an ineffective chimney, said researcher Elizabeth Klasen. Those measures have no impact or could even make emissions worse. Klasen is working with Checkley on a study comparing locally built and commercially available stoves that are meant to increase fuel efficiency and lower emissions.
Smith doubts that they will see a significant improvement.
“I’ve seen so many ‘improved’ stoves come and go that I’m cynical,” he said. “People use the word ‘improved’ as though it’s magical.”
Engineers and development workers have been experimenting with cookstove designs at least since the 1980s. They come in many styles, from mud-brick hearths to oil drums, with the most common model known as a “rocket stove.”
Because lower emissions depend on more efficient combustion, the secret lies in the stove’s combustion chamber, where “time, temperature and turbulence” are key, said Jim Jetter, an engineer in the U.S. Environmental Protection Agency’s Air Pollution Prevention and Control Division.
“The combustible gases have to have enough time to burn in the combustion chamber, they have to have high enough temperature to completely combust, and there needs to be turbulence, or good mixing in the combustion chamber,” said Jetter, who tests cookstoves in his laboratory.