ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-8-481-2008 Some considerations about Ångström exponent distributions Wagner F. 1 Silva A. M. 1 2 Centro de Geofísica, Évora, Portugal Universidade de Évora, Departamento de Física, Évora, Portugal 05 02 2008 8 3 481 489 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/8/481/2008/acp-8-481-2008.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/8/481/2008/acp-8-481-2008.pdf

A simulation study has been performed in order to show the influence of the aerosol optical depth (AOD) distribution together with the corresponding error distribution on the resulting Ångström exponent (AE) distribution. It will be shown that the Ångström exponent frequency of occurrence distribution is only normal distributed when the relative error at the two wavelengths used for estimation of the Ångström exponent is the same. In all other cases a shift of the maximum of the AE-distribution will occur. It will be demonstrated that the Ångström exponent (or the maximum of an AE distribution) will be systematically over- or underestimated depending on whether the relative error of the shorter wavelength is larger or smaller compared with the relative error of the longer wavelength. In such cases the AE distribution are also skewed.

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