Researchers have measured how dark brown carbon impacts the melting of snow.
Wildfires leave behind significant climate-changing particles that absorb sunlight and raise atmospheric temperatures. These aerosols, when deposited on snow, act like a thick wool blanket, making snow darker and reducing its ability to reflect sunlight.
However, the specific contributions of different types of smoke particles to these effects have not been fully understood. A recent study published in npj Climate and Atmospheric Science by researchers at Washington University in St. Louis reveals that dark-brown carbon (d-BrC) – which is light-absorbing and water-insoluble organic carbon – plays a much greater role in warming snow than previously thought. It is 1.6 times more effective at warming than what researchers initially considered to be the main agent, black carbon.
Previous studies have noted the presence of water-insoluble organic carbon on snow in regions like the Tibetan Plateau and other midlatitude areas. “However, no one has truly investigated their potential for melting snow,” said Rajan Chakrabarty, a professor at WashU’s McKelvey School of Engineering.
Chakrabarty’s PhD student, Ganesh Chelluboyina, who is a McDonnell International Scholars Academy fellow, and postdoctoral fellow Taveen Kapoor, have devoted much of their time at WashU tackling this issue.
The team describes d-BrC as an “evil cousin” of black carbon; similar to black carbon, it settles on snow, much like swapping out a white t-shirt for a dark brown poncho. Unlike other particles, these cannot be removed or faded to lose their light-absorbing properties. When snow loses its reflective quality and absorbs more heat, it raises the surrounding air temperature, fueling further warming.
If d-BrC is not considered, researchers have likely been undervaluing the extent of snow melt caused by wildfire smoke. This study will help create more precise climate models and measurements. As large wildfires increase in frequency, it will be crucial for policymakers to address this type of carbon to mitigate unusual snow melting. Although d-BrC absorbs slightly less light than black carbon, it compensates by being four times more common in wildfire smoke.
The research team aims to further explore the real-world impacts of d-BrC as they transition into experimental research. How can they conduct snow-aerosol experiments without going outdoors? They will utilize a four-foot-tall snow globe for their lab work.
“We’ll create snow by spraying atomized water droplets into the top of the chamber, then add aerosols on top,” Chelluboyina explained.
