A methodology to retrieve self‐consistent aerosol optical properties using common aircraft measurements

Abstract

Aerosol optical properties that include the extinction coefficient, single scattering albedo, and asymmetry factor are needed to calculate the radiative effects of aerosols. However, measurements of these properties are typically limited to a few wavelengths, and direct measurements of the asymmetry factor are not available. We describe and evaluate a retrieval methodology that uses commonly collected aircraft‐based measurements to derive self‐consistent aerosol optical properties for the majority of the solar spectrum. Measurements of aerosol scattering and absorption at three wavelengths are required to constrain this retrieval. We apply the retrieval to vertical profiles of biomass burning aerosol data collected by the University of Washington (UW) research aircraft during the Southern African Regional Science Initiative field campaign (SAFARI‐2000) and show that the retrieved (or “optically equivalent”) size distributions and wavelength‐dependent refractive indices reproduce available aerosol optical measurements within their respective uncertainties. The retrieved optically equivalent size distribution characteristics are consistent with past studies, but the wavelength‐dependent refractive indices retrieved using methods presented in this study are ∼14% (∼50%) greater than the real (imaginary) refractive indices retrieved from the Aerosol Robotic Network (AERONET) for three cases that were spatially and temporally colocated with the UW research aircraft. The retrieval presented in this study translates measured aerosol optical properties to parameters used directly as input to models and can be applied to any study that uses similar instrumentation. Provided that uncertainties are properly accounted for, self‐consistent aerosol optical properties derived from measurements strengthen the unique contribution of in situ data collection to the modeling community.