ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-9-13569-2009 UV aerosol indices from SCIAMACHY: introducing the SCattering Index (SCI) Penning de Vries M. 1 Beirle S. 1 Wagner T. 1 Max Planck Institute for Chemistry, J.-J.-Becherweg 27, 55128 Mainz, Germany 19 06 2009 9 3 13569 13592 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-discuss.net/9/13569/2009/acpd-9-13569-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/9/13569/2009/acpd-9-13569-2009.pdf

The Absorbing Aerosol Index (AAI) is a useful tool for detecting aerosols that absorb UV radiation – especially in cases where other aerosol retrievals fail, such as over bright surfaces (e.g. desert) and in the presence of clouds. The AAI does not, however, consider contributions from "scattering" (hardly absorbing) aerosols and clouds: they cause negative AAI values and are usually discarded. In this paper, we demonstrate the use of the AAI's negative counterpart, the SCattering Index (SCI) to detect "scattering" aerosols. Maps of seasonally averaged SCI show significantly enhanced values in summer in Southeast USA and Southeast Asia, pointing to high production of "scattering" aerosols (presumably mainly sulphate aerosols and organic aerosols) in this season. The application of a cloud filter makes the presence of "scattering" aerosols even more clear. In a comparison of AOT from AERONET and our Aerosol Indices from SCIAMACHY, good agreement was found for two AERONET stations in Southeast USA, and two stations in Africa. This fact confirms the suitability of SCI as a tool to detect "scattering" aerosols. <br><br> The combination of the UV Aerosol Indices AAI and SCI provides the unique possibility to characterise absorbing properties of aerosols from space. Accurate knowledge about aerosol absorption is crucial for the correct determination of the contribution of aerosols to the radiative budget.

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