JISAO Researchers Study Impact of Soot on Arctic Snow Melt Rates

Researchers at the University of Washington (UW) Joint Institute for the Study of the Atmosphere and Ocean (JISAO), in collaboration with the UW Department of Atmospheric Sciences, and the University of Hawaii, are currently engaged in research to determine whether ambient levels of soot in the Arctic are significant drivers of the region’s rising snow melt rates. Using snow samples from a broad array of sites within the Arctic Circle, the JISAO team melts and filters the sampled snow and then uses a spectrophotometer to measure the amount of light absorbed by the material on the filter. Comparison with a set of calibration standards determines the amount of soot per volume of snow and enables researchers determine how much of the light absorption was by soot versus other components, such as desert dust.

Background: In addition to greenhouse gases, pollutants such as particulate matter and ozone are also affecting global temperatures. Recent modeling studies indicate that the addition of soot to snow may be making a significant contribution to the observed warming, especially in the Northern Hemisphere. Forest fires, industrial processes, diesel vehicles, and other sources of incomplete combustion emit soot particles to the atmosphere which can be incorporated into snowflakes or deposited on snow, making the snow darker. Darker snow will be less reflective, absorbing more sunlight and possibly melting faster. Of particular interest is whether this effect is impacting the rate of melt in the Arctic, because melting in this region is proceeding at a quicker pace than expected and because the melting of snow and ice exposes the dark sea and land surface underneath. This results in more sunlight being absorbed by the surface, and therefore to a "feedback" cycle that produces more warming and more melting.

Significance: This is the first time such a broad set of measurements have been made of the soot content of snow across the Arctic. Upon completion of the data-collection phase, the researchers will compare their findings with those from previous modeling studies of soot content in snow to determine how much the soot is changing the reflectivity of the snow – and whether it is enough to be leading to accelerated melting. This research supports NOAA’s Mission Goal 2 - Understand climate variability and change to enhance society's ability to plan and respond.