Skip to Main content Skip to Navigation
Journal articles

Remote sensing of soot carbon - Part 2: Understanding the absorption Ångström exponent

Abstract : Recently, some authors have suggested that the absorption Ångström exponent (AAE) can be used to deduce the component aerosol absorption optical depths (AAODs) of carbonaceous aerosols in the AERONET database. This AAE approach presumes that AAE ≪ 1 for soot carbon, which contrasts the traditional small particle limit of AAE = 1 for soot carbon. Thus, we provide an overview of the AERONET retrieval, and we investigate how the microphysics of carbonaceous aerosols can be interpreted in the AERONET AAE product. We find that AAE ≪ 1 in the AERONET database requires large coarse mode fractions and/or imaginary refractive indices that increase with wavelength. Neither of these characteristics are consistent with the current definition of soot carbon, so we explore other possibilities for the cause of AAE ≪ 1. AAE is related to particle size, and coarse mode particles have a smaller AAE than fine mode particles for a given aerosol mixture of species. We also note that the mineral goethite has an imaginary refractive index that increases with wavelength, is very common in dust regions, and can easily contribute to AAE ≪ 1. We find that AAE ≪ 1 can not be caused by soot carbon, unless soot carbon has an imaginary refractive index that increases with wavelength throughout the visible and near-infrared spectrums. Finally, AAE is not a robust parameter for separating carbonaceous absorption from dust aerosol absorption in the AERONET database.
Document type :
Journal articles
Complete list of metadata
Contributor : Nathalie POTHIER Connect in order to contact the contributor
Submitted on : Friday, June 3, 2022 - 10:00:06 AM
Last modification on : Saturday, June 4, 2022 - 3:36:38 AM


Publisher files allowed on an open archive


Distributed under a Creative Commons Attribution 4.0 International License




G. L. Schuster, O. Dubovik, A. Arola, T. F. Eck, B. N. Holben. Remote sensing of soot carbon - Part 2: Understanding the absorption Ångström exponent. Atmospheric Chemistry and Physics, European Geosciences Union, 2016, 16, pp.1587-1602. ⟨10.5194/acp-16-1587-2016⟩. ⟨insu-03686215⟩



Record views


Files downloads