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Observed vertical redistribution of black carbon and other insoluble light‐absorbing particles in melting snow
Author(s) -
Doherty Sarah J.,
Grenfell Thomas C.,
Forsström Sanja,
Hegg Dean L.,
Brandt Richard E.,
Warren Stephen G.
Publication year - 2013
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/jgrd.50235
Subject(s) - snow , meltwater , snowpack , scavenging , carbon black , snowmelt , albedo (alchemy) , atmospheric sciences , particle (ecology) , environmental science , snow field , radiative forcing , aerosol , chemistry , geology , meteorology , geomorphology , geography , snow cover , art , biochemistry , natural rubber , oceanography , organic chemistry , performance art , art history , antioxidant
Light‐absorbing impurities in snow reduce snow albedo, producing a positive radiative forcing, warming the surface air and snowpack, and accelerating snow melt. As the snow melts, black carbon (BC) and other insoluble light‐absorbing particulate impurities (ILAP) are retained at the snow surface because their scavenging efficiency with meltwater is <100%, so concentrations of ILAP in surface snow increase with snow melt, further reducing snow albedo. The magnitude of this positive feedback depends on the scavenging efficiency of BC and other ILAP with snow meltwater. We present results from field measurements of the vertical distribution of BC and other ILAP in snow near Barrow (Alaska), the Dye‐2 station in Greenland and Tromsø (Norway) during the melt season. Amplification factors due to melt are calculated for the concentrations in surface snow of BC and all ILAP. At Barrow and Dye‐2, melt scavenging rates are estimated. Melt amplification appears generally to be confined to the top few centimeters of the snowpack, where it increases concentrations of BC and other ILAP by up to a factor of about five. Scavenging fractions of ILAP due to percolation of meltwater are estimated at 10–30%, with the rates for BC being comparable or a few percent lower. The lack of distinction may result from the particles in snow being internal mixtures of both BC and other ILAP, so that scavenging efficiencies for these internally mixed particles are determined by the total particle size and hydrophobicity rather than being different for individual particle components.