Extinction efficiencies of coated absorbing aerosols measured by cavity ring down aerosol spectrometry
1Department of Environmental Sciences, Weizmann Institute, Rehovot, 76100, Israel
2Dept. of Atmospheric Sciences, The Hebrew Univ. of Jerusalem, Jerusalem, 91904, Israel
3Physics Services, Weizmann Institute, Rehovot, 76100, Israel
Abstract. In this study, we measure the extinction efficiency at 532 nm of absorbing aerosol particles coated with a non-absorbing solid and liquid organic shell with coating thickness varying between 5 and 100 nm using cavity ring down aerosol spectrometry. For this purpose, we use nigrosin, an organic black dye, as a model absorbing core and two non–absorbing organic substances as shells, glutaric acid (GA) and Di-Ethyl-Hexyl-Sebacate (DEHS). The measured behavior of the coated particles is consistent with Mie calculations of core-shell particles. Errors between measured and calculated values for nigrosin coated with GA and DEHS are between 0.5% and 10.5% and between 0.5% and 9%, respectively. However, it is evident that the calculations are in better agreement with the measured results for thinner coatings. Possible reasons for these discrepancies are discussed.