ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-6-8713-2006 Classification of aerosol properties derived from AERONET direct sun data Gobbi G. P. 1 Kaufman Y. J. 2 Koren I. 3 Eck T. F. 2 4 Inst. Scienze dell’ Atmosfera e del Clima, CNR, Rome, Italy NASA/Goddard Space Flight Center, 613.2, Greenbelt MD 20771, USA Dep. of Environ. Sciences Weizmann Institute, Rehovot 76100, Israel GEST, University of Maryland, Baltimore, MD, USA 14 09 2006 6 5 8713 8726 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/6/8713/2006/acpd-6-8713-2006.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/6/8713/2006/acpd-6-8713-2006.pdf

Aerosol spectral measurements by sunphotometers can be characterized by three independent pieces of information: 1) the optical thickness (AOT), a measure of the column aerosol concentration, 2) the optical thickness average spectral dependence, given by the Angstrom exponent (α), and 3) the spectral curvature of α (δα). We propose a simple graphical method to visually convert (α, δα) to the contribution of fine aerosol to the AOT and the size of the fine aerosols. This information can be used to track mixtures of pollution aerosol with dust, to distinguish aerosol growth from cloud contamination and to observe aerosol humidification. The graphical method is applied to the analysis of yearly records at 8 sites in 3 continents, characterized by different levels of pollution, biomass burning and mineral dust concentrations. Results depict the dominance of fine mode aerosols in driving the AOT at polluted sites. In stable meteorological conditions, we see an increase in the size of the fine aerosol as the pollution stagnates and increases in optical thickness. Coexistence of coarse and fine particles is evidenced at the polluted sites downwind of arid regions.