New type of soot from wildfires to be probed for role in climate change

Flaming wildfires around the world emit about one-third of the soot in the atmosphere and are blamed for contributing to changes in climate.

Richard Axelbaum, Rajan Chakrabarty

Recently, researchers found that these fires emit a new type of soot particle, known as a superaggregate, with distinct physical and optical properties. But little is known about how soot superaggregates form and their ultimate impact on the climate and human health, because obtaining particle samples from wildfires is extremely difficult and poses a risk to human life.

Rajan Chakrabarty, in the School of Engineering & Applied Science at Washington University in St. Louis, has received a three-year, $300,000 grant from the National Science Foundation to generate soot superaggregates in his lab that mimic those from real-world wildfires. He plans to use a patent-pending, negative gravity flame aerosol reactor to produce the particles and to study how they are formed and their microphysical properties in detail. Richard Axelbaum, the Stifel & Quinette Jens Professor of Environmental Engineering Science, is co-principal investigator on the project.

In addition to determining the particles' impact on climate change and human health, the findings will assist policymakers and regulators in developing new and effective monitoring, control and mitigation strategies, said Chakrabarty, assistant professor of energy, environmental & chemical engineering.

Soot is created by incomplete combustion of gaseous hydrocarbons in high-temperature combustion, ranging from the burning of biomass to engines and furnaces. In some parts of southeast Asia and Russia, flaming wildfires contribute to nearly two-thirds of soot emissions in the atmosphere. Depending on the size of the superaggregates, these particles could impact radiative forcing in the otherwise ignored longer solar wavelengths, Chakrabarty said. From the health perspective, these particles could get deposited deep inside human lungs, similar to sub-micron-size soot aggregates emitted from diesel engines.

"Our research is designed to bring about a potentially transformative change in our understanding of soot formation mechanism in large-scale flaming fires, the optical characteristics of the emitted particle, and their impact on climate," Chakrabarty said.

As part of the project, Chakrabarty and Axelbaum will work with the university's Institute for School Partnership to provide summer workshops on combustion science and climate change for 20 local high school math and science teachers from districts in underserved communities. During the school year, teachers and students will be able to ask Chakrabarty and graduate students in his lab questions related to combustion science and climate.

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