AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Light Absorption by Ammonium Sulfate with Carbon Black Inclusions: Experiments, Mie Theory and Effective Medium Approximations
JAMES RADNEY, Christopher Zangmeister, National Institute of Standards and Technology
Abstract Number: 473 Working Group: Instrumentation and Methods
Abstract The refractive index of aerosols is one of the key parameters in determining the optical properties, and hence the radiative forcing, with Mie theory being the calculation method of choice due to its ease of use and computational efficiency. Typically, for complex multi-component aerosols, e.g. biomass burning aerosols with black carbon inclusions, only an effective refractive index corresponding to a specific fuel type or specific burn can be retrieved from measurements. Here, we measure the extinction and absorption cross-sections of size- and mass-selected particles composed of non-absorbing ammonium sulfate with strongly absorbing carbon black inclusions at multiple mass fractions. We then compare refractive indices retrieved using Mie theory assuming: 1) homogeneous particles, 2) a core-shell configuration and 3) a variety of effective medium approximations (e.g. volume mixing, Maxwell-Garnett, Bruggman, etc.) to those obtained from spectroscopic ellipsometry utilizing the same mixtures. The goal of this work is to determine if consistent refractive indices for the two materials (ammonium sulfate and carbon black) across the multiple mass fractions can be obtained from these approximations thereby validating these simplistic computational approaches to a complex modeling problem.