When Marshall Burke moved to California in 1998, wildfires were not top of mind. They flared up occasionally, “but it wasn’t something people really thought about much,” recalled Burke, an associate professor of environmental social sciences in the Stanford Doerr School of Sustainability.
That perception has changed as wildfires have become much more frequent and their smoke has begun to affect millions more people. “Things are headed in the wrong direction from an air quality perspective,” Burke said. Together with colleagues, he has worked to quantify how wildfire smoke affects air quality and public health, using data-driven analysis to inform potential solutions.
Here are five essential facts based on Burke’s research.
Wildfire smoke is rapidly reversing decades of U.S. air quality progress
Following the Clean Air Act of 1963 and subsequent amendments to the law, air quality in the United States dramatically improved. Communities once shrouded in haze regained visibility, and decreased pollution from vehicles and industry contributed to improved public health. Burke and colleagues, including Stanford’s Michael Wara and Marissa Childs of the University of Washington, have found that wildfire smoke is now undermining this hard-won success.
The researchers developed new algorithms and analyzed particle pollution data from satellites and ground sensors to estimate smoke exposure across the United States. Their analyses show that the number of people exposed to smoke-caused unhealthy air at least one day a year grew 27-fold in just 10 years. Since 2016, wildfire smoke has slowed or reversed air quality improvements in 35 states. “We are rapidly eroding those decades of previous progress in the span of five to 10 years, due to just this one source, wildfire smoke,” said Burke.
Wildfire smoke is now a nationwide problem
Once thought of as a seasonal phenomenon in fire-prone Western states, wildfire smoke now affects communities coast to coast, with more than 1.5 million people across the U.S. living in locations routinely exposed to extremely heavy smoke days. The smoke contains toxic fine particles known as PM2.5, which can lodge deep in the lungs and enter our bloodstream, harming lung, heart, and brain health. “This is now a very shared burden across the U.S.,” said Burke.
Burke, together with Stanford scholar Sam Heft-Neal, found that smoke exposure is linked to increased emergency department visits, excess mortality, and preterm birth rates. In 2021, the researchers found that a 3.4% increase in preterm birth risk resulted from one week of elevated smoke exposure, even when pollution levels were low enough to meet “good” or “moderate” air quality standards established by federal regulators.
In addition to health burdens, economic analyses show wildfire smoke exposure can reduce labor productivity and student test scores.
In the week following an extreme smoke day, emergency department visits for asthma, COPD, and coughing increase by 30-110%.
Household actions can reduce smoke exposure
Evidence from sensor data shows that individual behaviors such as closing windows, sealing homes, and running air conditioners or purifiers with HEPA filters can substantially lower smoke exposure. Actions at the community level, such as setting up clean air shelters in libraries and schools, may also benefit health, though their impact needs more research. Ongoing studies by Burke and others are quantifying the impact of practical interventions and why some people effectively keep pollution out of their homes during smoke waves while others do not. “Understanding what works to limit exposure is an important next step for us,” said Burke.
Updating air quality rules can empower communities to better manage wildfire smoke
Under the Clean Air Act, local regulators face penalties if pollution concentrations exceed certain thresholds. Yet wildfire smoke is increasingly becoming a major source of hazardous air pollution in many areas and currently gets a regulatory pass. Agencies can apply for exemptions for pollution exceedances caused by wildfires.
The exemption has a logic, as wildfire smoke often drifts across jurisdictions. “But, if everyone makes that argument, then no one’s controlling wildfire smoke anywhere,” said Burke. One way to break the cycle is to update air quality regulations to promote long-term smoke reduction strategies. A potential change could involve exempting controlled burns – fires intentionally set to reduce fuel loads and prevent larger wildfires – from counting against local air quality goals, which discourages approval.
To enable more informed decisions, Burke and colleagues are studying how prescribed burns affect smoke pollution over time. Preliminary research from Burke and PhD student Iván Higuera-Mendieta suggests that a decade-long prescribed fire program could reduce the cumulative concentration of smoke PM2.5 by about 23% compared to a control scenario without the treatment.
Climate change, wildfires, and air quality are intertwined
Climate change is one of the factors driving more frequent and intense wildfires, which in turn worsen air quality. Accurately accounting for economic and health damage caused by wildfire smoke can provide a clearer understanding of the costs and benefits of climate action.
Together with researchers Minghao Qiu, Christopher Callahan, Iván Higuera Mendieta, Lisa Rennels, and Noah Diffenbaugh, Burke is working to estimate deaths from wildfire smoke in the U.S. that could be avoided through climate mitigation. Preliminary analyses suggest incorporating this data could double current estimates for the social cost of carbon emissions in the U.S. In terms of excess deaths, Burke said, “the wildfire smoke damages are as large as the combined effects of all other climate impacts that have been studied in the U.S.”
For more information
Burke is also a senior fellow at the Stanford Woods Institute for the Environment, the Freeman Spogli Institute for International Studies, and the Stanford Institute for Economic Policy Research (SIEPR); an associate professor (by courtesy) of Earth system science; and a member of Bio-X and the Wu Tsai Neurosciences Institute.
Callahan and Rennels are postdoctoral scholars in the Stanford Doerr School of Sustainability – Callahan in Earth system science and Rennels in environmental social sciences. Rennels is also a Stanford Energy Postdoctoral Fellow in the school’s Precourt Institute for Energy.
Diffenbaugh is the Kara J Foundation Professor and Kimmelman Family Senior Fellow in the Doerr School of Sustainability.
Wara is senior director for policy at the Sustainability Accelerator and a senior research scholar at the Woods Institute for the Environment, both within the school.
Heft-Neal is a senior research scholar at the Center on Food Security and the Environment.
This story was originally published by Stanford Doerr School for Sustainability.
Writer
Ula Chrobak
