Measured Impact of Black Carbon on Snow Surface Albedo

ODELLE HADLEY (1), Thomas Kirchstetter (1), Mark Flanner (2)

(1) Lawrence Berkeley National Laboratory (2) University of Michigan, Ann Arbor

     Abstract Number: 381
     Last modified: May 11, 2010

Abstract
Black carbon (BC) affects global and regional climates through different mechanisms, including the deposition to and darkening of surface snow and ice. Modeling studies attribute increased air temperature and decline in snow and ice extent in the Northern Hemisphere partly to BC deposition on the surface. If the models are correct, this BC effect may be the second leading cause of observed ice retreat, nearly equal to the greenhouse gas effect in some regions. Observational validation of the modeled BC impact on snow has yet to be published. Field studies dating back to the early 1980s measured atmospheric BC deposition to snow and ice in the arctic, but the BC effect on snow albedo and melting has been difficult to observe directly because the albedo reduction is small and often masked by other natural variables, and the transport of BC in melting snow has not yet been evaluated through measurement.

This study presents a comparison between the measured and modeled spectral albedo (300 to 2500nm) of laboratory-made snow with effective radii of 50, 100, and 200 microns and BC concentrations from 0 to 2000 ppbm. Ice grain morphology and size distributions are measured using a digital microscope. BC concentrations are measured using a spectrometer equipped with a liquid waveguide capillary cell. In addition to albedo measurements, the transport of BC in melting snow has been measured in laboratory-made and natural snow. These measurements provide the first observations of a BC concentration enhancement in melting snow and can be used to improve the snowpack scavenging parameter of BC used in models.