Sky-high smoke
Wildfire smoke lofted into atmosphere could affect Earth’s climate
image:
Satellite observations of wildfire-driven thunderstorm activity and smoke plume. These images are from a June 16, 2022 active fire in New Mexico.
view moreCredit: NOAA GOES Satellite
Key takeaways
- Harvard atmospheric scientists directly sampled 5-day old wildfire smoke in the upper troposphere and found large particles that are not reflected in current climate models.
- The large particles had a measurable cooling effect, with potential implications for future climate predictions
Some wildfires are so intense, they create their own weather – thunderstorms driven by heat that hurtle smoke as high as 10 miles into the sky like giant chimneys.
When these smoke plumes reach the thin, calm air of the upper troposphere and lower stratosphere, they can persist for weeks or even months – yet their exact effects on the Earth’s climate aren’t well known because they’re difficult to capture and measure.
An atmospheric science team in the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) took an audacious swing at directly observing fresh wildfire smoke that found its way into the uppermost troposphere, about nine miles above Earth’s surface.
In a study published in Science Advances, the researchers report that unusually large particles they observed inside a wildfire-induced, high-altitude smoke plume had a significant cooling effect on that region, a phenomenon with potential consequences for the Earth’s climate yet aren’t incorporated into current climate models.
“We’re seeing more and more wildfires in Canada, the western U.S., all over the world,” said senior author Frank Keutsch, Stonington Professor of Engineering and Atmospheric Science at SEAS. “We are particularly interested in what the impact is on climate, and extending from that, what is the impact on atmospheric composition – the things that we care about, for example, the stratospheric ozone layer that protects us from UV radiation.”
Absorbed or scattered sunlight
Wildfire smoke, as well as other aerosols like industrial air pollution, can change the amount of radiation that gets to the ground by absorbing sunlight or scattering it back toward space. Better understanding the behavior of high-altitude smoke clouds could lead to new insights into the balance between incoming and outgoing radiation, and thus, how Earth processes like the hydrological cycle might be responding to fires, Keutsch explained.
For example, said study co-author and project scientist John Dykema, local heating caused by the smoke absorbing sunlight could cause atmospheric circulation to change, which could in turn shift positions of jet streams and may have implications for weather. “I think all of these things are possible, and we don’t currently have enough information to say which way they could go,” he said.
The research team used the NASA ER-2 high-altitude aircraft outfitted with specialized equipment to make unprecedented observations of a smoke plume that climbed into the uppermost troposphere shortly after the eruption of a New Mexico wildfire in June 2022.
Aboard the aircraft that was shared with other research groups, they deployed a portable optical spectrometer that measures the concentration and size of particles, as well as an instrument that measures plume composition — complemented by an instrument from a group at Purdue University to identify smoke particles.
With the help of geostationary satellite technology, the researchers were able to pinpoint the plume, fly into it, and capture detailed information from within it just five days post-fire. This compares with previous observers who’d managed to measure stratospheric smoke that was several weeks old.
Coagulated aerosols
Within the young plume, the Harvard team observed concentrations of surprisingly large aerosols, about 500 nanometers in diameter, or double the size of typical smoke aerosols at lower altitudes. With the help of modeling experts at Colorado State University, they showed that efficient particle coagulation could explain their large observed size.
“Particles can coagulate at any place in the atmosphere,” said lead author and former Ph.D. student Yaowei Li. “But in that specific region, the air mixes very slowly. That allows wildfire smoke particles to remain concentrated and collide more often, making coagulation much more efficient.”
These larger-sized particles, they continued, had a much stronger cooling effect, increasing outgoing radiation by 30-36% compared with smaller smoke particles typically found at lower altitudes. This effect has not been included in current climate models. The results could have important implications for how scientists understand the Earth’s future climate.
“Our study provides new insights to better constrain how particles from these specific phenomena of wildfire-driven thunderstorms affect the Earth’s energy budget,” Li said.
The study was co-authored by Harvard researchers Xu Feng, Jasna Pittman, Bruce Daube, Steven Wofsy, and Loretta Mickley. Other co-authors were David Peterson, Xiaoli Shen, Nicole June, Michael Fromm, Theodore McHardy, Justin Jacquot, Jonathan Dean-Day, Anita Rapp, Kenneth Bowman, Daniel Cziczo, and Jeffrey Pierce.
The research was supported by NASA under the Earth Venture Suborbital-3 program awards for the Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) mission, for which Keutsch is the Deputy-PI. Additional support came from the Naval Research Laboratory, the National Science Foundation, and the Salata Institute for Climate and Sustainability at Harvard.
Journal
Science Advances
Method of Research
Observational study
Article Title
Enhanced Radiative Cooling by Large Aerosol Particles from Wildfire-Driven Thunderstorms
Article Publication Date
10-Dec-2025
Chemical traces of 2023 Canadian wildfires detected in Maryland months after smoke subsided
A new University of Maryland study of campus air samples revealed that chemical compounds from Canada’s historic 2023 fires lingered in the air, forming an ‘atmospheric soup.’
image:
Sun behind wildfire smoke haze on June 7, 2023.
view moreCredit: Sharon L. Chapman
Jn 2023, Canada’s worst wildfire season on record produced so much smoke that it spilled across national borders into the United States. At times, a thick haze enveloped much of the U.S. East Coast and triggered “Code Purple” and “Code Maroon” alerts—the most hazardous air quality warning categories—in the Washington, D.C. region.
More than 1,000 miles from where the smoke originated, a group of University of Maryland researchers seized the rare opportunity to directly analyze wildfire plumes—a pollutant that plagues the U.S. West Coast far more frequently than the East Coast. Their findings, published in the journal Environmental Science: Atmospheres, revealed that chemical compounds from Canada’s wildfires remained in the atmosphere in College Park, Md., months after the smoke subsided, raising concerns about the potential health and environmental effects.
“Even when the Air Quality Index was good—long after the fires started to dwindle—we still found similar compounds that we saw during the Canadian wildfire event,” said study senior author Akua Asa-Awuku, a professor in UMD’s Department of Chemical and Biomolecular Engineering.
In the future, their findings could help improve predictive models used to study wildfires and their effects. Most chemical composition studies of long-range smoke plumes rely on federal agency satellites and planes that fly through wildfires to collect samples. On-the-ground testing is rarer, making UMD’s study unique.
“To our knowledge, no study data provides a molecular-level composition of the 2023 Canadian wildfire plumes,” said the study’s lead author, Esther Olonimoyo, a UMD chemistry Ph.D. student. “This is a pretty complex area of study where more work still needs to be done in understanding the chemical composition of wildfire plumes.”
When Canadian wildfire smoke first arrived on campus, Asa-Awuku, Olonimoyo and their co-authors collaborated with Department of Atmospheric and Oceanic Science researchers to collect air samples from the rooftop of the university’s Atlantic Building in June 2023, August 2023 and February 2024.
The researchers took those samples back to Asa-Awuku’s Environmental Aerosol Research Laboratory for chemical analysis using a high-pressure liquid chromatography method developed by Olonimoyo and study co-author Candice Duncan, an assistant professor in the Department of Environmental Science and Technology.
Their method was designed to quickly and accurately analyze organic acids, which are carbon-rich compounds—including ones found in wildfire smoke—that can negatively affect the climate and human health when concentrated in the atmosphere. While smoke plumes peaked on campus in June 2023 and visibly dissipated by August, the researchers discovered that air samples collected in August still contained the chemical traces of wildfire smoke.
Those samples were collected on a day when the Air Quality Index (AQI) was good, suggesting that compounds from wildfire plumes may linger in the atmosphere longer than expected.
“We see the persistence of compounds in the atmosphere beyond what the air quality indices tell us,” Olonimoyo said. “That raises public health concerns that people might still be exposed to certain compounds even after air quality indices have significantly improved.”
The researchers identified different classes of carbonaceous chemicals in the air, including some that could be toxic to humans in high concentrations. Asa-Awuku noted that the AQI measures five major pollutants and does not account for a wider range of chemical species—including atoms, molecules, ions and radicals—in the atmosphere.
“The AQI provides a general assessment of overall air quality for the region,” Asa-Awuku said. “The AQI was high when there was a lot of particulate matter from the wildfire emissions, but the AQI tells us little about the chemical composition of particulates.”
It wasn’t until February 2024—eight months after the wildfires—that researchers saw a significant decrease in wildfire-associated compounds. Asa-Awuku suggested that the compounds they observed may have interacted with gases in the atmosphere, triggering chemical reactions that made them stick around longer.
“A lot of the compounds that we analyzed don’t dissipate like a primary emission, which is emitted directly into the atmosphere,” Asa-Awuku explained. “They are persistent over time and space, which suggests that they are part of an atmospheric soup that’s generating more and more of these organic compounds with time.”
Studying these compounds—and their ability to dissolve in water—can help researchers understand their longer-term impact on the environment. Some chemical compounds from wildfire plumes react with water vapor and wind up in clouds, so when it rains, they can infiltrate the soil and alter the Earth’s natural biogeochemical cycle.
Moving forward, Olonimoyo plans to analyze these compounds in greater detail and identify the ones with unique signatures. Ultimately, she hopes their findings will help the scientific community make better predictions about wildfires and their impact on people and the environment.
“Knowing the molecular composition of these plumes is very important in model predictions,” Olonimoyo said. “The scientific community can make better predictions when they have more accurate knowledge, and it also helps us assess the likely implications if certain compounds are present in the atmosphere.”
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In addition to Olonimoyo, Asa-Awuku and Duncan, UMD co-authors included Yue Li, director of the Mass Spectrometry Facility in UMD’s Department of Chemistry and Biochemistry, and Department of Chemical and Biomolecular Engineering Ph.D. students Martin Changman Ahn and Dewansh Rastogi (Ph.D. ’23).
The paper, “Chemical signatures of water-soluble organic carbon (WSOC) fraction of long-range transported wildfire PM2.5 from Canada to the United States Mid-Atlantic region,” was published in Environmental Science: Atmospheres on November 25, 2025.
This research was supported by the U.S. National Science Foundation. This article does not necessarily reflect the views of this organization.
Journal
Environmental Science Atmospheres
Method of Research
Observational study
Article Title
Chemical signatures of water-soluble organic carbon (WSOC) fraction of long-range transported wildfire PM2.5 from Canada to the United States Mid-Atlantic region
GeoFlame VISION: Using AI and satellite imagery to predict future wildfire risk
A new computer model produces a dynamic wildfire risk map, starting with the state of California
Society for Risk Analysis
Washington, D.C., December 9, 2025 – Wildfires pose a significant threat across the southwestern United States, due to the region’s unique topography and weather conditions. Accurately identifying locations at the highest risk of a severe wildfire is critical for implementing preventive measures.
With this goal in mind, scientists from the University at Buffalo have developed GeoFlame VISION, a proposed computer model that uses AI and satellite imagery to produce a dynamic wildfire risk map at a granular spatiotemporal scale for the entire United States. The authors will present a case study of California using their model on Dec. 9 at the Society for Risk Analysis Annual Meeting in Washington, D.C.
“This novel approach of integrating remote sensing data with machine learning and AI will not only help with efficient wildfire mitigation, but also aid in decision-making related to land management and the controlled expansion of Wildland-Urban-Interface (WUI) regions – which in turn can lower the risk of wildfire-induced damages to the critical infrastructures and WUI communities in the future”, says Sayanti Mukherjee, assistant professor of industrial and systems engineering at the University at Buffalo and corresponding author of the study.
Preliminary findings from the dynamic wildfire risk map of California:
The eastern, southwestern, and northwestern parts of California are significantly more vulnerable to wildfires than other regions. This is mainly because the impact of the dry, warm Santa Ana winds is particularly pronounced in California's southwestern and northern regions, increasing the likelihood of wildfires there.
According to the map, the California counties of Mono, Inyo, Mariposa, Ventura, and Tulare are at the highest risk of wildfire. The 2022 Airport Fire in Inyo and the 2017 Thomas Fire in Ventura reinforce the credibility and accuracy of this finding.
The model shows that Los Angeles and Mono counties are in wildfire hotspots due to their dry climates, unique vegetation, and prevailing wind directions.
The key predictors of wildfire risk are climate, topographical, and vegetation factors.
Wind speed plays a significant role in the occurrence of a severe wildfire, followed by the normalized difference vegetation index (NDVI) and precipitation.
“The wildfire risk in a region not only depends on the topographical, landcover, and weather-related variables, but also on the built environment, such as the buildings and power grid infrastructure, which is often overlooked in the traditional physics-based wildfire spread models,” says Poulomee Roy, lead author of the study and a doctoral candidate at the University at Buffalo. “Thus, the interactions among all these factors -- which we include in our study -- are instrumental in modeling the dynamic wildfire risk.”
To create the map, the researchers used satellite imagery data from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) to extract information on historical burned areas from 2015 to 2022 at a weekly time scale (with small areas marked burned or unburned). This dataset was integrated with information on variables such as topography, elevation, climate, vegetation, windspeed, and the locations of critical infrastructure, including residential buildings and power stations. Using advanced vision-based AI and other technologies, a pixel-based predictive analysis of the wildfire-burnt areas was then performed. The map is about 92% accurate at predicting dynamic wildfire risk at a granular spatiotemporal scale (based on real data from past wildfires).
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About Society for Risk Analysis
The Society for Risk Analysis (SRA) is a multidisciplinary, global organization dedicated to advancing the science and practice of risk analysis. Founded in 1980, SRA brings together researchers, practitioners, and policymakers from diverse fields including engineering, public health, environmental science, economics, and decision theory. The Society fosters collaboration and communication on risk assessment, management, and communication to inform decision-making and protect public well-being. SRA supports a wide range of scholarly activities, publications, and conferences. Learn more at www.sra.org.
EDITORS NOTE:
This research will be presented on December 9 at 8:30 EST at the Society for Risk Analysis (SRA) Annual Conference at the Downtown Westin Hotel in Washington, D.C. SRA Annual Conference welcomes press attendance. Please contact Emma Scott at emma@bigvoicecomm.com to register.
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