Photopolarimetric measurements in the Atlanta metropolitan area, and their potential for improving characterization of absorbing aerosols

Large uncertainties in the effects of atmospheric aerosols are among the major factors currently limiting our understanding of climate change. A key question is whether atmospheric aerosols contribute to warming or cooling of the climate system. Since the sign of radiative forcing is controlled by the ability of aerosol particles to absorb light, the information on the single scattering albedo of different aerosol types is clearly very desirable.

This study explores the potential for retrieving the aerosol single scattering albedo using ground-based polarimetric measurements conducted under urban aerosol-laden conditions. We utilized data from several AERONET sites representative of urban pollution cases. In addition, new measurements were carried out in the Atlanta Metropolitan Area using a CIMEL sun-sky photometer with a polarimetric channel in conjunction with a suite of in-situ aerosol instruments including a Magee Scientific Aethalometer, Particle Soot Absorption Photometer, Nephelometer, and an EC/OC instrument. Several techniques to retrieve the single scattering albedo were tested. A detailed analysis of the sensitivity of polarization to aerosol size distribution, composition, amount of black carbon and its mixing state were performed using a polarimetric radiative transfer code. The paper will report the results of this work and discuss the advantages and limitations of polarimetric measurements for the retrieval of the aerosol single scattering albedo.