Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 6 2 2006 10.5194/acpd-6-1841-2006 http://www.atmos-chem-phys-discuss.net/6/1841/2006/ http://www.atmos-chem-phys-discuss.net/6/1841/2006/acpd-6-1841-2006.html http://www.atmos-chem-phys-discuss.net/6/1841/2006/acpd-6-1841-2006.pdf 1841 1866 2006-03-14 Strong spectral dependence of light absorption by organic carbon particles formed by propane combustion M. Schnaiter M. Gimmler I. Llamas C. Linke C. Jäger H. Mutschke Institute of Meteorology and Climate Research, Forschungszentrum Karlsruhe, Germany Astrophysical Institute and University Observatory, University of Jena, Germany We have measured the extinction and absorption cross sections of carbon particles emitted by a propane diffusion flame both in an aerosol chamber and on size-segregated samples deposited on optical windows. The absorption cross section, the single scattering albedo and the Ångström exponent show drastic dependencies both on the C/O ratio and on the particle size. This is interpretated as being due to the appearance of nucleation modes of smaller organic particles at higher C/O ratios, which were detected by SMPS measurements and partially by TEM analysis. The spectral range of the validity of the absorption power-law (Ångström exponent) model is investigated by vacuum ultraviolet extinction measurements. These measurements give also indications for a preferentially aromatic nature of the OC component of the flame products.