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Investigation of Two Optical Methods for Aerosol‐Type Classification Extended to a Northern Indian Ocean Site
Stockholm University, Faculty of Science, Department of Meteorology .ORCID iD: 0000-0001-6868-9658
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
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2019 (English)In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 124, no 15, p. 8743-8763Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2019. Vol. 124, no 15, p. 8743-8763
National Category
Earth and Related Environmental Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
URN: urn:nbn:se:su:diva-172377DOI: 10.1029/2018JD029685ISI: 000482475000023OAI: oai:DiVA.org:su-172377DiVA, id: diva2:1346565
Available from: 2019-08-28 Created: 2019-08-28 Last updated: 2019-09-16Bibliographically approved
In thesis
1. Multiple perspectives on absorbing aerosols over the northern Indian Ocean and Asia
Open this publication in new window or tab >>Multiple perspectives on absorbing aerosols over the northern Indian Ocean and Asia
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Aerosol particles in the atmosphere scatter and absorb solar radiation, and thereby affect the Earth's energy budget, but the magnitude of the overall radiative effect due to aerosol-radiation interactions is uncertain. In particular, the impact of absorbing aerosol particles, mainly black carbon (BC), organic carbon and dust, is not completely understood. A large variety of absorbing aerosols can be found in Asia and over adjacent oceans due to huge urban, biomass burning and desert areas. This thesis focuses on the investigation of atmospheric aerosols over the northern Indian Ocean and Asia from multiple perspectives. This includes surface and vertical observations of physical and chemical particle properties by in-situ and remote sensing instruments as well as an investigation of the representation of absorbing aerosols in general circulation models. One main focus is on the identification of BC-containing particles at the marine remote Maldives Climate Observatory in Hanimaadhoo (MCOH) which is frequently influenced by continental air masses containing anthropogenic aerosols. During an intensive field campaign, vertical measurements of aerosol particles were performed with a Lidar and unmanned aerial vehicles. Elevated layers of absorbing aerosol above the marine boundary layer were found frequently when air masses had their source over the northern Indian Peninsula. However, determining a complete profile of particle absorption only from Lidar measurements is linked to high uncertainties. Long-term surface measurements of particle absorption and scattering together with observations of aerosol chemical composition at MCOH are used to evaluate purely optical methods for aerosol characterization. These optical methods are found to give reasonable estimates of particle types but they can not replace detailed chemical measurements. An additional comparison study of various instruments for determination of BC mass give potentially very diverse results, highlighting the complexity of the quantification of BC-containing particles. The investigation of the representation of absorbing aerosols over Asia in general circulation models reveals firstly that the particle absorption is generally underestimated in global climate models, and secondly that the range in aerosol absorption determined from major changes of emissions, meteorology and particle optical properties can not reach the large inter-model diversity. 

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology, Stockholm University, 2019. p. 48
Keywords
aerosols, black carbon, air pollution, South Asia
National Category
Earth and Related Environmental Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-172375 (URN)978-91-7797-791-9 (ISBN)978-91-7797-792-6 (ISBN)
Public defence
2019-10-11, William-Olssonsalen, Geovetenskaps hus, Svante Arrhenius väg 14, Stockholm, 10:00 (English)
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Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2019-09-18 Created: 2019-08-28 Last updated: 2019-09-12Bibliographically approved

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Höpner, FriederikeBender, Frida A.-M.Ekman, Annica M. L.Andersson, AugustGustafsson, ÖrjanLeck, Caroline
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