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The World Health Organization considers air pollution the greatest environmental threat to public health, estimating that it kills more than 7 million people a year and attributing almost half of those deaths to household smoke from open fires and traditional stoves. To combat the problem, the United Nations and other groups have launched initiatives aimed at increasing access to clean-cooking methods—including subsidies for high-efficiency stoves.
But research by University of Pennsylvania’s Susanna B. Berkouwer and Chicago Booth’s Joshua Dean, who conducted a study in Nairobi, Kenya, suggests that when it comes to the health effects of air pollution, the spikes associated with traditional cooking methods are only one part of a larger picture. Study participants who adopted high-efficiency cookstoves self-reported lower levels of respiratory symptoms such as headaches and coughing. Yet switching to these cleaner stoves had no effect on blood pressure, blood oxygen levels, or medical diagnoses such as pneumonia.
The findings suggest that respiratory symptoms are associated with the peaks in air pollution caused by cooking, while clinical health symptoms such as blood pressure are more closely tied to average levels of pollution exposure. The city’s ambient pollution—from sources such as industrial activity, vehicles, and agricultural burning—remained the same during the 3.5-year-long study.
Beyond the improvements in respiratory symptoms that they bring, high-efficiency cookstoves have other climate and social welfare benefits that make their adoption worthwhile and could justify a subsidy, the researchers argue.
“Burning less charcoal does reduce the peaks during cooking, and that’s correlated with reductions in self-recorded diagnoses,” says Dean. “But it doesn’t move average pollution exposure at all, partly because these peaks are just not that big a part of the day.” In short, he says, “in urban settings where people face both peak and ambient pollution, alleviating the peaks for improved cooking is not sufficient to make long-term impacts on chronic health conditions.”
This is particularly true in Nairobi, a city of 4.4 million people. Berkouwer and Dean’s experiment there offered one set of participants a hefty subsidy to induce them to buy high-efficiency stoves. For others, they set it low. These participants did not purchase a stove and thus served as a control group.
In the study, high-efficiency stoves significantly reduced participants’ exposure to harmful particle emissions while cooking. However, they did little to change people’s overall average and peak exposure levels throughout the monitoring period.
Participants carried a backpack throughout their day equipped with devices that measured particulate matter and carbon monoxide—essentially, their exposure to ambient and peak emissions. They self-reported respiratory symptoms and later responded to a survey about chronic health diagnoses.
“Exposure levels during cooking with traditional stoves were appallingly high,” says Dean, “and these peaks seem to be a really important factor in the respiratory symptoms that people experienced.” Yet, there was no reduction in chronic health outcomes or reported diagnoses, Dean says, nor did they observe any changes in blood pressure or pulse oxygenation.
But high-efficiency cookstoves nevertheless yielded big benefits, the researchers say. For one, they saved households money. Berkouwer and Dean calculate that charcoal purchases amounted to about 20 percent of household income, and high-efficiency cookstoves cut a household’s charcoal consumption by nearly half.
“Even if the health benefits to high-efficiency cookstoves were less than might be expected, there would still be massive financial savings,” says Dean. “These households spent a huge amount of their money on energy. The stoves retailed for $40 at the time of the study, and the savings were more than $120 during the first year. That return on investment can help people obtain a livelihood.”
A second benefit is that the stoves could be among the most cost-effective ways to reduce carbon emissions. Each high-efficiency cookstove reduces CO2 emissions by approximately 3.5 tons per year. The researchers’ data indicate that this is far more cost-effective than many other carbon-abatement technologies. They calculate the cost of emissions reduction for the stoves to be about $5 per ton, while electric vehicles, for instance, struggle to break $100 per ton.
Moreover, the technology is scalable. Billions of people worldwide rely on traditional stoves, and replacing those stoves with cleaner versions would cut millions of tons of carbon emissions. Switching to high-efficiency stoves could therefore play a significant role in reducing greenhouse-gas emissions, Dean says. He notes that there is also high additionality—the emissions reductions achieved by replacing cookstoves would not occur otherwise. Many households that received subsidized stoves otherwise wouldn’t have purchased one, and nearly four years after the study, about 85 percent of them still have it.
Susanna B. Berkouwer and Joshua Dean, “Private Actions in the Presence of Externalities: The Health Impacts of Reducing Air Pollution Peaks but Not Ambient Exposure,” Working paper, March 2024.
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