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Volume 10, issue 10 | Copyright

Special issue: CHemistry and AeRosols Mediterranean EXperiments (ChArMEx)...

Atmos. Meas. Tech., 10, 3743-3781, 2017
https://doi.org/10.5194/amt-10-3743-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 12 Oct 2017

Research article | 12 Oct 2017

Advanced characterisation of aerosol size properties from measurements of spectral optical depth using the GRASP algorithm

Benjamin Torres1,2, Oleg Dubovik1, David Fuertes1,2, Gregory Schuster3, Victoria Eugenia Cachorro4, Tatsiana Lapyonok1, Philippe Goloub1, Luc Blarel1, Africa Barreto5,4,6, Marc Mallet7, Carlos Toledano4, and Didier Tanré1 Benjamin Torres et al.
  • 1Laboratoire d'Optique Amosphérique, Université des Sciences et Technologies de Lille, Villeneuve d'Ascq, France
  • 2GRASP-SAS, Remote sensing developments, Université des Sciences et Technologies de Lille, Villeneuve d'Ascq, France
  • 3NASA Langley Research Center, Hampton, VA 23681, USA
  • 4Group of Atmospheric Optics, Valladolid University, Valladolid, Spain
  • 5Cimel Electronique, Paris, France
  • 6Izaña Atmospheric Research Center, Spanish Meteorological Agency, Tenerife, Spain
  • 7CNRM UMR 3589, Météo-France/CNRS, Toulouse, France

Abstract. This study evaluates the potential of using aerosol optical depth (τa) measurements to characterise the microphysical and optical properties of atmospheric aerosols. With this aim, we used the recently developed GRASP (Generalized Retrieval of Aerosol and Surface Properties) code for numerical testing of six different aerosol models with different aerosol loads. The direct numerical simulations (self-consistency tests) indicate that the GRASP-AOD retrieval provides modal aerosol optical depths (fine and coarse) to within 0.01 of the input values. The retrieval of the fine-mode radius, width and volume concentration are stable and precise if the real part of the refractive index is known. The coarse-mode properties are less accurate, but they are significantly improved when additional a priori information is available. The tests with random simulated errors show that the uncertainty in the bimodal log-normal size distribution parameters increases as the aerosol load decreases. Similarly, the reduction in the spectral range diminishes the stability of the retrieved parameters. In addition to these numerical studies, we used optical depth observations at eight AERONET locations to validate our results with the standard AERONET inversion products. We found that bimodal log-normal size distributions serve as useful input assumptions, especially when the measurements have inadequate spectral coverage and/or limited accuracy, such as moon photometry. Comparisons of the mode median radii between GRASP-AOD and AERONET indicate average differences of 0.013µm for the fine mode and typical values of 0.2–0.3µm for the coarse mode. The dominant mode (i.e. fine or coarse) indicates a 10 % difference in mode radii between the GRASP-AOD and AERONET inversions, and the average of the difference in volume concentration is around 17 % for both modes. The retrieved values of the fine-mode τa(500) using GRASP-AOD are generally between those values obtained by the standard AERONET inversion and the values obtained by the AERONET spectral deconvolution algorithm (SDA), with differences typically lower than 0.02 between GRASP-AOD and both algorithms. Finally, we present some examples of application of GRASP-AOD inversion using moon photometry and the airborne PLASMA sun photometer during the ChArMEx summer 2013 campaign in the western Mediterranean.

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This study evaluates the potential of using only aerosol optical depth measurements to characterise the microphysical and optical properties of atmospheric aerosols. With this aim, we used the recently developed GRASP algorithm. The practical motivation for the present study is the large amount of optical-depth-only measurements that exist in the ground-based networks. The retrievals could complete an existing data set of aerosol properties that is key to understanding aerosol climate effects.
This study evaluates the potential of using only aerosol optical depth measurements to...
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