By Kathleen Berger, Executive Producer for Science and Technology

Wildfires have sparked new research in the Aerosol Interdisciplinary Research Group’s lab, AIR Lab, at Washington University in St. Louis. Principal Investigator Rajan Chakrabarty is igniting new areas of study following his “wildfire chasing” in the western U.S. in 2019.

To conduct a comprehensive analysis of what makes up wildfire smoke plumes, Chakrabarty’s team spent 45 days traveling to wildfire locations, where they sampled gaseous smoke and aerosol species and analyzed their chemical and optical properties.

During their sampling of ground and airborne smoke from large-scale wildfires, Chakrabarty’s team discovered an unusually strong light absorber in the plumes that wasn’t black carbon, accounting for more than half of the observed total absorption. They discovered that the stealthy, dark brown carbon particles in wildfires likely contribute to much more climate warming than previously recognized. This discovery shifted Chakrabarty’s attention to the stratosphere.

“Once emitted into the stratosphere, the particles can cause enhanced warming there. The lifetime of these particles is up to six months,” said Chakrabarty, the Harold D. Jolley Career Development Associate Professor of Energy, Environmental, and Chemical Engineering at Washington University in St. Louis.

Given the intensity of the threat posed by light-absorbing particles—also known as climate heaters—in the stratosphere, the team is exploring the possibility of arming the stratosphere with particles that reflect light, to have a cooling effect. The goal is to offset global warming caused by all other factors. The aerosols for potential stratospheric injection are tested with specialized equipment in Chakrabarty’s lab. The ultimate aim is to inject these particles into the stratosphere to reflect the sun’s rays before they can warm the planet.

“This particular modality of solar radiation management is called stratospheric aerosol injection (SAI),” said Chakrabarty.

Chakrabarty and his collaborators are investigating SAI with a $1.5 million grant from the Simons Foundation International. WashU researchers have engineered specialized equipment to test different particles and determine the best one for the job. The team is studying how these particles will interact with solar radiation and ozone over time to ensure their effective deployment.

This new project aims to inform climate projections and offer potential solutions. For example, in the case of a heat dome with excessive and dangerous heat, Chakrabarty suggested considering the approach as a temporary fix.

“This is more for local or regional warming,” he said. “You’d take a load of this material in an aircraft, fly it all the way up to the stratosphere, and inject it. We’re only trying to address a small piece of the problem.”

The team is starting by creating a database of optical and chemical properties for the most promising aerosol candidates for the mission.

“Injection is like preventing the spread of a disease,” Chakrabarty added, for perspective. “In this case, the ‘disease’ is rising temperatures. What we’re trying to inject are small mirrors to reflect sunlight, lowering the Earth’s temperature. It’s more of a band-aid solution, trying to stop the symptoms until we find a permanent solution.”