In this paper, Sun-photometer multichannel measurements of aerosol optical depths (AODs) in the visible and near-infrared spectral ranges, and Ångström parameters of the plume issued from the Pacaya volcano, Guatemala, are presented for the first time. These observations, made during a short-term campaign carried out on 29 and 30 January 2011, indicate a diluted (AODs lower than 0.1) volcanic plume composed of small particles (Ångström exponent ∼1.0 on 29 January and ∼1.4 on 30 January).

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... are consistent with an ash-free plume. Finally, the impact of the choice of different wavelength pairs for the calculation of the Ångström parameters from the spectral AOD observations is tested and critically discussed.