Air pollution, identified by the World Health Organization as the foremost environmental threat to human health, claims between 7 and 9 million lives annually, representing 10%–15% of global deaths. In response to this critical issue, Wharton professor of business economics and public policy Susanna Berkouwer has studied the nuanced causes of air pollution, focusing on the crucial distinctions between short-term exposure peaks and continuous sustained exposure.

“High levels of air pollution significantly decrease life expectancy, but existing regulations primarily focus on the annual or daily averages of pollution, overlooking short-term fluctuations that many people experience. Short bursts of pollution are often caused by indoor cooking,” said Berkouwer.

Their paper, co-authored with the University of Chicago’s Joshua Dean, argues that shedding light on these nuances is crucial for creating effective environmental regulations to address this global health crisis. Should policies focus on how everyday individuals can reduce peak pollution, or should they address broader, ambient air quality concerns?

“Improved cookstoves have a huge impact in that short window of cooking – but not on the 24-hour average.”— Susanna Berkouwer

Short- and Long-term Air Pollution Impact Your Health Differently

The researchers conducted a field study in Nairobi, Kenya, examining the impact of improved cookstove adoption on pollution and health. Through randomized subsidies and credit access, they generated random variation in the adoption of improved cookstoves and followed up with participants 3.5 years later, employing high-frequency monitoring techniques and detailed health measurements.

To measure air pollution, each participant in the study wore a backpack with devices that recorded tiny particles and carbon monoxide in the air every minute for 48 hours. The study found that the improved stove greatly reduced peak cooking emissions by 42%, significantly improving air quality during cooking. There was also a substantial decrease in average exposure to pollution during cooking in the treatment group using improved stoves compared to the control group (50 micrograms per cubic meter vs. 33 micrograms).

However, the overall impact on daily pollution exposure was much less pronounced, due to the limited time people spent cooking each day (approximately 9% of the time). “Improved cookstoves have a huge impact in that short window of cooking – but not on the 24-hour average,” Berkouwer said.

When it comes to health impacts, the improved stove led to a statistically significant decrease (0.24 standard deviation) in self-reported respiratory symptoms, including sore throat, headache, cough, and runny nose. These improvements were not consistently reflected in more clinical health measurements like blood pressure and oxygen levels.

“We find that addressing the short-term peaks really helps resolve the kind of symptoms you’d get if you spend time around a campfire. But we don’t see any impact on longer-term medical diagnoses like pneumonia,” said Berkouwer.

“Providing improved stoves for free would be a considerably cheaper way to reduce carbon emissions than almost any other technology available today.”— Susanna Berkouwer

Climate Policy Needs to Address Diverse Causes of Air Pollution

The results have important policy implications, as they underscore the need for nuanced measures to address the diverse causes of air pollution. While individual efforts, such as using improved stoves, may offer modest health benefits in the short term, the research suggests that government regulations targeting broader environmental factors could yield more substantial and enduring health improvements. “You might need government intervention to address the ambient pollution — it could be regulating emissions from cars or coal-fired power plants,” Berkouwer said.

Given that billions of people living in cities, especially in poorer countries, face daily exposure to high pollution levels, the study’s implications are global. More than 90% of pollution-related deaths occur in low- and middle-income countries, affecting around 4 billion people who lack access to improved cookstoves, resulting in sporadic bursts of high pollution.

Additionally, the study is relevant to international development and climate policy, in terms of the impact of subsidies on improved cookstove usage. Offering subsidies between $30–$40 resulted in a 72 percentage point-higher ownership rate after 3.5 years. Combining that with the findings on reduced emissions, the study estimates that providing improved stoves for free would cost around $4.90 for every ton of carbon dioxide reduced — considerably lower than many other available methods.

People using these improved stoves in urban areas also continue to save money on charcoal, about $86 per year, suggesting that investing in initiatives like improved cookstoves can be an effective and economical strategy for wealthier countries and international organizations to contribute to carbon reduction efforts. “There’s huge financial benefits to be had,” said Berkouwer. “Providing improved stoves for free would be a considerably cheaper way to reduce carbon emissions than almost any other technology available today.”