Determining Aerosol Angstrom Absorption Coefficients: Comparison of Full Spectrum Integrating Sphere Reflection Spectroscopy with 3 and 7 Wavelength Filter Absorption Methods

Aerosols have been identified as a major uncertainty in climate forcing due to both direct and indirect effects. Both scattering and absorption of radiation is of concern in the direct effect, with absorption of solar radiation a major uncertainty. Both primary (black carbon) and secondary organic aerosols can contribute to absorption along with some inorganic dusts. These contributors show variance in their broad band optical spectra that can be described using a simple exponential fit. The enhanced absorption in the UV or nearby visible regions leads to variance in the Angstrom Absorption Exponents (AAE). This variance in the AAE's can be useful in interpreting the relative contributions to observed aerosol absorption. This work will overview the use of integrating sphere reflection spectroscopy to obtain full spectrum (280-900 nm) aerosol absorption and associated AAEs. A comparison will be presented with AAEs obtained from a 3-wavelength PSAP (Particle Soot Absorption Photometer) and a 7-wavelength aethalometer on the same samples under field conditions. The comparison highlights the importance and need for full spectrum determinations for improved aerosol absorption evaluations.

This work is supported by the Office of Science (BER) U.S. Department of Energy under Grant No. DE-FG02-07ER6429, as part of DOE Atmospheric Systems Research (ASR).