Thermal-optical analysis of snow samples – challenges and perspectives introduced via the occurrence of mineral dust

Abstract. The determination of mineral dust and elemental carbon in snow samples is of great interest, as both compounds are known as light absorbing snow impurities. Different analytical methods have to be used to quantify both compounds. Still, the occurrence of mineral dust, which contains hematite, leads to a bias in the quantification of elemental carbon via thermal-optical analysis. Here we present an approach which utilizes this interference to determine the concentration of hematite via thermal-optical analysis using a Lab OC/EC Aerosol Analyzer (Sunset Laboratory Inc.) and the EUSAAR2 protocol. Therefore, the temperature dependency of the transmittance signal determined during the calibration phase, i.e. when all carbonaceous compounds are already removed, is evaluated. Converting the transmittance signal into an attenuation, a linear relationship between this attenuation and the hematite loading is obtained for loadings ranging from 10 to 100 µgFe cm-2. Furthermore, the approach allows to identify samples which need to be re-evaluated, as the analysis of elemental carbon is biased by mineral dust. We discuss the successful application of the method, designed for snow samples, to ambient air samples containing mineral dust, and the limitations of the method when other iron compounds besides hematite are present.