ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-2987-2012 Sources of discrepancy between aerosol optical depth obtained from AERONET and in-situ aircraft profiles Esteve A. R. 1 Ogren J. A. 2 Sheridan P. J. 2 Andrews E. 2 3 Holben B. N. 4 Utrillas M. P. 1 Department of Earth Physics and Thermodynamics, University of Valencia, Valencia, Spain Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado, USA Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA Goddard Space Flight Center, National Aeronautics and Space Administration, Greenbelt, Maryland, USA 27 03 2012 12 6 2987 3003 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/2987/2012/acp-12-2987-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/2987/2012/acp-12-2987-2012.pdf

Aerosol optical properties were measured by NOAA's Airborne Aerosol Observatory over Bondville, Illinois, during more than two years using a light aircraft. Measured properties included total light scattering, backscattering, and absorption, while calculated parameters included aerosol optical depth (AOD), Ångström exponent, single-scattering albedo, hemispheric backscatter fraction, asymmetry parameter, and submicrometer mode fraction of scattering. The in-situ aircraft measurements are compared here with AERONET measurements and retrievals of the aerosol optical properties at the same location, although it is difficult to verify the AERONET retrieval algorithm at a site that is not highly polluted. The comparison reveals discrepancies between the aerosol properties retrieved from AERONET and from in-situ aircraft measurements. These discrepancies are smaller for the AOD, while the biggest discrepancies are for the other derived aerosol properties. Possible sources of discrepancy between the AOD measured by AERONET and the one calculated from the in-situ aircraft measurements are investigated. The largest portion of the AOD discrepancy is likely due to an incorrect adjustment to ambient RH of the scattering coefficient. Another significant part (along with uncertain nephelometer truncation corrections) may come from the possibility that there might be less aerosol below the lowest flight altitude or that the aircraft inlet excludes aerosol particles larger than 5–7 μm diameter.

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