Investigation of the specific attenuation cross-section of aerosols deposited on fiber filters with a polar photometer to determine black carbon

A polar photometer was used to investigate phase functions of glass fiber f ilters with varying aerosol particle loadings. Angle-resolved analysis reve aled that the shape of the normalized phase function S-n(theta) in the tran smitted hemisphere is independent of aerosol composition and determined exc lusively by the fibrous filter matrix, while S-n(theta) in the reflected he misphere depends on the scattering properties of the aerosol sample. Cross sensitivities of the specific attenuation cross section with respect to sca ttering components were examined with well-defined laboratory generated aer osol samples. The specific attenuation cross section at theta = 165 degrees (reflected hemisphere) was found considerably less dependent of the aeroso l composition than any angular position in the transmitted hemisphere, and is therefore best suited for the determination of black carbon (BC). The an gular position theta = 165 degrees was calibrated with an almost pure BC te st aerosol. BC mass loadings of ambient aerosol samples (0.15-20 mu g cm(-2 )) determined with this calibration function were in good agreement with va lues analyzed by coulometry. (C) 1999 Elsevier Science Ltd. All rights rese rved.