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  • Investigation of Two Optica...
    Höpner, F.; Bender, F. A.‐M.; Ekman, A. M. L.; Andersson, A.; Gustafsson, Ö.; Leck, C.

    Journal of geophysical research. Atmospheres, 16 August 2019, Volume: 124, Issue: 15
    Journal Article

    Methods for determining aerosol types in cases where chemical composition measurements are not available are useful for improved aerosol radiative forcing estimates. In this study, two aerosol characterization methods by Cazorla et al. (2013, https://doi.org/10.5194/acp-13-9337-2013; CA13) and Costabile et al. (2013, https://doi.org/10.5194/acp-13-2455-2013; CO13) using wavelength‐dependent particle absorption and scattering are used, to assess their applicability and examine their limitations. Long‐term ambient particle optical property and chemical composition (major inorganic ions and bulk carbon) measurements from the Maldives Climate Observatory Hanimaadhoo as well as concurrent air mass trajectories are utilized to test the classifications based on the determined absorption Ångström exponent, scattering Ångström exponent, and single scattering albedo. The resulting aerosol types from the CA13 method show a good qualitative agreement with the particle chemical composition and air mass origin. In general, the size differentiation using the scattering Ångström exponent works very well for both methods, while the composition identification depending mainly on the absorption Ångström exponent can result in aerosol misclassifications at Maldives Climate Observatory Hanimaadhoo. To broaden the applicability of the CA13 method, we suggest to include an underlying marine aerosol group in the classification scheme. The classification of the CO13 method is less clear, and its applicability is limited when it is extended to aerosols in this environment at ambient humidity. Key Points Optical aerosol classifications conform reasonable well with chemical measurements and air mass origin analysis The extension of optical characterization methods to a remote marine site is limited due to strong aerosol mixing and humidification An underlying sea spray category should be considered for optical aerosol characterization at sites with marine influence