München 2004 – scientific programme
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UP: Umweltphysik
UP 21: Aerosol und Messtechnik
UP 21.1: Fachvortrag
Tuesday, March 23, 2004, 16:30–16:45, HS 221
Multi-angle absorption photometry - a new method for the measurement of aerosol light absorption and atmospheric black carbon — •Andreas Petzold1 and Hansgerd Kramer2 — 1Institut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt Oberpfaffenhofen, 82234 Wessling — 2Thermo ESM Andersen Instruments, Frauenauracher Str. 96, 91056 Erlangen
A new method is presented which determines the aerosol light absorption from the simultaneous measurement of radiation passing through and scattered back from a particle-loaded fibre filter. The measurement is performed at three detection angles to resolve the influence of light scattering aerosol components on the angular distribution of the back scattered radiation. The fraction of light absorbed by the deposited aerosol (absorbance ABS) is obtained from a radiative transfer scheme. The compensation of light scattering effects in filter-based aerosol absorption measurements is considerably improved. The detection limit is 3.5 × 10−4 absorbance units. The uncertainty of the absorbance is ± 12%. The evaluation of the method using field data yielded an average mass specific absorption coefficient of 9.1 - 10.7 m2/g at λ = 0.55 µm for atmospheric black carbon in urban air. Agreement between particle absorption coefficients obtained by multi-angle absorption photometry and optical in situ reference methods is very good for various aerosol types (kersone flame, graphite, ambient aerosol). First background air measurements at the high-alpine site Jungfraujoch demonstrate the applicability of the method also to clean background air.