Specifying light absorbing properties of aerosol particles in fresh snow samples, collected at the Environmental Research Station Schneefernerhaus (UFS), Zugspitze

Abstract. Darkening of pristine white areas on Earth could happen when light absorbing particles are deposited on snow and ice surfaces. Airborne particles like mineral dust, ashes or carbonaceous aerosols are able to reduce the snow and ice albedo already by a small quantity of deposited particles. In this study we developed a laboratory analysis method to address mass and absorption properties of snow particles simultaneously. For a set of snow samples, taken at the Environmental Research Station Schneefernerhaus (UFS) during winter 2016/2017, we combine the determination of refractory Black Carbon mass (rBC) by a Single Particle Soot Photometer (SP2) with photo acoustic aerosol absorption spectroscopy at three distinct wavelengths across the visible spectral range (PAAS-3 λ ). For the calibration of the method, Fullerene standard aerosol was used and its mass specific absorption cross section was determined. The analysis of the UFS snow sample measurements reveals a significant difference between the particle masses determined from the PAAS-3 λ and the SP2 data. Our findings suggest that the light absorbing particles included in the snow could not only be composed of rBC but must have particulate matter of different nature. This result is confirmed by Environmental Scanning Electron Microscopy (ESEM) and single particle fluorescence measurements with the Waveband Integrated Bioaerosol Sensor (WIBS-4) which both revealed a significant portion of biological material to be present in the snow samples.