Research Shows How Wildfires May Have Larger Effects on Cloud Formation and Climate Change

As forest fires continue to grow in frequency and size around the world, new research from Carnegie Mellon University scientists shows how chemical aging of the particles emitted by these fires can lead to increased cloud formation and intense storm build-up in the atmosphere. The research was published online in the journal Science Advances.

“The introduction of large quantities of ice nucleation particles from these fires can have a significant impact on the microphysics of clouds, whether subcooled cloud droplets freeze or remain liquid, and on the tendency of clouds to precipitate,” said Ryan Sullivan, Associate Professor of Chemistry and Mechanical engineering. Understanding these effects is a key factor in accurately modeling the Earth’s climate and how it could continue to change.

Building on the research published last year by Sullivan’s team at the Center for Atmospheric Particle Studies, the authors collected various plant materials, burned them, and analyzed the particles emitted in the smoke. In particular, the team was interested in ice nucleation particles, rare types of particles that catalyze the formation of ice crystals in the atmosphere at higher than usual temperatures and thus strongly influence climatic processes, including cloud formation and the question of whether or not a cloud fails can. In fact, most of the precipitation over land comes from ice-laden clouds.

While it was already well known that particles freshly released from burning biomass – such as tall grass, shrubs, and trees – can greatly affect ice nucleation, Sullivan’s team was keen to find out the effects of these particles on their days and weeks of traveling Atmosphere and experienced chemical aging. Using a special chamber reactor, mass spectrometers, electron microscopy and an innovative microfluidic droplet freezing technique, the researchers analyzed the particles that are formed when various types of plant material are burned, such as those that occur in forest fires, and prescribed burns and simulated the aging processes these particles undergo in the atmosphere.

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A diagram showing the various aging processes of aerosol for burning biomass in the atmosphere.

Typically, ice nucleation particles lose their effectiveness as they age in the atmosphere. In this study, however, the researchers found that the ice nucleation ability of particles emitted by burning biomass actually increases when they experience simulated atmospheric aging. This represents a completely different framework for investigating how the climate-related properties of an important episodic particle source in the atmosphere develop.

“This is because the aging of the atmosphere causes the loss of particle coatings that are initially present on the smoke particles that hide the ice-active surface sites,” Sullivan said. “These locations are the mineral particles produced from the combustion of biomass fuels itself that we reported on in the Proceedings of the National Academy of Sciences last year.”

The data from this study could have a huge impact on future research on forest fires and climate change, said Lydia Jahl, who recently received her Ph.D. in chemistry from Carnegie Mellon in Sullivan’s group.

“We have estimated that burning just one square meter of grassland can affect the concentration of ice nucleation particles in hundreds of thousands of cubic kilometers of the atmosphere,” said Jahl. “Climate modelers could use our data further to determine, among other things, how forest fire emissions affect the balance between incoming solar radiation and outgoing terrestrial radiation.”

Other authors on this study were Thomas A. Brubaker, Bailey B. Bowers, and William D. Fahy of Carnegie Mellon; Micahel J. Poland, now from McDaniel College; Leif G. Jahn, now from the University of Texas at Austin; Kerrigan P. Cain, now with NASA’s Glenn Research Center; and Sara Graves, now from the University of California at Los Angeles.

Funding for this study was provided by grants from the National Science Foundation.

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