17 Mar 2022
17 Mar 2022
Status: this preprint is currently under review for the journal ACP.

Circular Polarization in Atmospheric Aerosols

Santiago Gassó1,2 and Kirk David Knobelspiesse3 Santiago Gassó and Kirk David Knobelspiesse
  • 1ESSIC, University of Maryland, College Park, 20740, USA
  • 2Code 613, Climate and Radiation Laboratory, GSFC/NASA, Greenbelt, 20771, USA
  • 3Code 616, Ocean Ecology Laboratory, GSFC/NASA, Greenbelt, 20771, USA

Abstract. Recent technological advances have demonstrated the feasibility of deploying spaceborne optical detectors with full polarimetric capabilities. The measurement of all four Stokes coefficients opens significant new opportunities for atmospheric aerosol studies and applications. While considerable amounts of attention have been dedicated to sensors with sensitivity to the total intensity and linear polarization (represented by Stokes coefficients I, U, Q), there has been less attention to the additional information brought by measuring circular polarization (coefficient V). This report fills this gap in knowledge by providing an overview of aerosol sources of circular polarization in the atmosphere and discusses possible remote sensing signatures.

In this manuscript, circularly polarized radiation that results from the interaction of incident unpolarized radiation are considered in three physical settings: optical activity originating in biogenic aerosols, alignment of non-spherical particles in the presence of electrical fields (such as dust, smoke, and volcanic ash) and aerosol multiple scattering effects. Observational and theoretical evidence of, and the settings and conditions for non-zero aerosol circular polarization generated from incident unpolarized radiation are here gathered and discussed. In addition, novel radiative transfer simulations are shown to illustrate notable spectral and other features where circular polarization may provide additional information that is possibly independent from total intensity and linear polarization only observations.

Current techniques for detection of aerosol composition (also referred as aerosol type) from space provide limited information. Remote identification of aerosols such as smoke, volcanic ash, and dust particles can only be accomplished with some degree of confidence for moderate to high concentrations. When the same aerosols are found at lower concentrations (but still high enough to be of importance for air quality and other concerns), these methods often produce ambiguous results. Thus, the exploration of additional optical techniques is of interest to improve remote detection of aerosol composition. This study is presented as an overview with a goal to provide a new perspective on an overlooked optical property and to trigger interest in further exploration of this subject.

Santiago Gassó and Kirk David Knobelspiesse

Status: open (until 24 Jun 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-55', Anonymous Referee #1, 24 May 2022 reply

Santiago Gassó and Kirk David Knobelspiesse

Santiago Gassó and Kirk David Knobelspiesse


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Short summary
New satellite observing technology is sensitive to the polarization of reflected sunlight. Atmospheric aerosols interact with light and can create polarization. This means we can learn about aerosols from space. This manuscript considers circular polarization, a special category of polarization with distinctive features that could bring new insights. We review existing literature and make novel computations to consider this previously overlooked category of polarization.