Mass specific optical absorption coefficients of mineral dust components measured by a multi wavelength photoacoustic spectrometer. The effect of HULIS coverage on the absorption spectra

Mass specific aerosol optical absorption coefficients of various mineral dust components, including silicate clays (illite, kaolin and bentonite), oxides (quartz, hematite and rutile), and carbonate (limestone) were determined at the operational wavelengths of a multi-wavelength photoacoustic instrument (i.e. at 1064, 532, 355 and 266 nm). These photoacoustically measured spectra can be used on one hand in global radiative forcing calculations, and on the other hand for validating optical absorption spectra typically deduced from measurements on bulk phase samples of mineral dust components by using indirect measurement methods. These inter-comparisons prove that there is a strong need for standardized sample preparation and measurement methodology in case of bulk phase measurements. The effect of HULIS (i.e. humic-like substances) coverage on the mass specific aerosol optical absorption coefficients are discussed as well.