Light absorption from particulate impurities in snow and ice determined by spectrophotometric analysis of filters.

Light absorption by particulate impurities in snow and ice can affect the surface albedo and is important for the climate. The absorption properties of these particles can be determined by collecting and melting snow samples and extracting the particulate material by filtration of the meltwater. This paper describes the optical design and testing of a new instrument to measure the absorption spectrum from 400 to 750 nm wavelength of the particles collected on filters using an "integrating-sandwich" configuration. The measured absorption is shown to be unaffected by scattering of light from the deposited particulates. A set of calibration standards is used to derive an upper limit for the concentration of black carbon (BC) in the snow. The wavelength dependence of the absorption spectra from 450 to 600 nm is used to calculate an absorption Ångstrom exponent for the aerosol. This exponent is used to estimate the actual BC concentration in the snow samples as well as the relative contributions of BC and non-BC constituents to the absorption of solar radiation integrated over the wavelength band 300 to 750 nm.

Source attribution of black carbon in Arctic snow.

Snow samples obtained at 36 sites in Alaska, Canada, Greenland, Russia, and the Arctic Ocean in early 2007 were analyzed for light-absorbing aerosol concentration together with a suite of associated chemical species. The light absorption data, interpreted as black carbon concentrations, and other chemical data were input into the EPA PMF 1.1 receptor model to explore the sources for black carbon in the snow. The analysis found four factors or sources: two distinct biomass burning sources, a pollution source, and a marine source. The first three of these were responsible for essentially all of the black carbon, with the two biomass sources (encompassing both open and closed combustion) together accounting for >90% of the black carbon.

Visible and near-ultraviolet absorption spectrum of ice from transmission of solar radiation into snow.

Snow is a scattering-dominated medium whose scattering is independent of wavelength at 350-600 nm. The attenuation of solar radiation in snow can be used to infer the spectral absorption coefficient of pure ice, by reference to a known value at 600 nm. The method is applied to clean Antarctic snow; the absorption minimum is at 390 nm, and the inferred absorption coefficient is lower than even the lowest values of the Antarctic Muon and Neutrino Detector Array (AMANDA) experiment on glacier ice: The absorption length is at least 700 m, by comparison with 240 m for AMANDA and 10 m from laboratory attenuation measurements.