Optical and thermal measurements of black carbon aerosol contents in different environments: variation of the specific attenuation cross-section

In optical analysers devoted to the analysis of atmospheric black carbon concentration, the specific attenuation cross-section, a is the factor used to convert the attenuation of a light beam due to the absorption of aerosols deposited on a filter into their black carbon content. We have tried to gain further insight for a suitable choice of sigma value, using both optical analysis (with an aethalometer) and thermal analysis of black carbon aerosols and comparison of the two sets of results. Samples which were investigated originating from varying environments, including suburban areas, tropical areas where biomass buming was prevalent and from more remote locations. In a given type of atmospheric environment, a values are found to be constant.