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Abstract
The interaction of aerosol particles and solar radiation plays an important role in the global radiative balance. Discussed in this work is the use of cavity ring down spectroscopy for the measurement of complex refractive indices for homogeneous aerosols and aerosol mixtures. Application of a novel calibration method improved the uncertainty of extinction cross section measurements collected from 10.6% to 2%. This technique retrieved complex refractive index measurements in close agreement with the values predicted by the volume-fraction mixing rule for an absorbing binary mixture composed of 2-(2-benzotriazol-2-yl)-6-dodecyl-4-methylphenol (BDMP), a strong UV absorber, and squalane. These measurements demonstrate high sensitivity and the ability to measure atmospherically relevant absorption. Measurements of aerosol external mixtures demonstrated the ability to measure the contribution of multiple-charged particles to measured extinction cross sections at small particle diameters. An initial investigation into the importance of phase in aerosol optical properties is also described.