Articles | Volume 10, issue 3
Research article
08 Mar 2017
Research article |  | 08 Mar 2017

Retrievals of aerosol optical and microphysical properties from Imaging Polar Nephelometer scattering measurements

W. Reed Espinosa, Lorraine A. Remer, Oleg Dubovik, Luke Ziemba, Andreas Beyersdorf, Daniel Orozco, Gregory Schuster, Tatyana Lapyonok, David Fuertes, and J. Vanderlei Martins

Abstract. A method for the retrieval of aerosol optical and microphysical properties from in situ light-scattering measurements is presented and the results are compared with existing measurement techniques. The Generalized Retrieval of Aerosol and Surface Properties (GRASP) is applied to airborne and laboratory measurements made by a novel polar nephelometer. This instrument, the Polarized Imaging Nephelometer (PI-Neph), is capable of making high-accuracy field measurements of phase function and degree of linear polarization, at three visible wavelengths, over a wide angular range of 3 to 177°. The resulting retrieval produces particle size distributions (PSDs) that agree, within experimental error, with measurements made by commercial optical particle counters (OPCs). Additionally, the retrieved real part of the refractive index is generally found to be within the predicted error of 0.02 from the expected values for three species of humidified salt particles, with a refractive index that is well established. The airborne measurements used in this work were made aboard the NASA DC-8 aircraft during the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) field campaign, and the inversion of this data represents the first aerosol retrievals of airborne polar nephelometer data. The results provide confidence in the real refractive index product, as well as in the retrieval's ability to accurately determine PSD, without assumptions about refractive index that are required by the majority of OPCs.

Short summary
Aerosols, and their interaction with clouds, play a key role in the climate of our planet but many of their properties are poorly understood. We present a new method for estimating the size, shape and optical constants of atmospheric particles from light-scattering measurements made both in the laboratory and aboard an aircraft. This method is shown to have sufficient accuracy to potentially reduce existing uncertainties, particularly in airborne measurements.