Six-year observations of aerosol optical properties at a southern African grassland savannah site

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Venter , M , Beukes , J P , van Zyl , P G , Vakkari , V , Virkkula , A , Josipovic , M , Kulmala , M & Laakso , L 2020 , ' Six-year observations of aerosol optical properties at a southern African grassland savannah site ' , Atmospheric Environment , vol. 230 , 117477 .

Title: Six-year observations of aerosol optical properties at a southern African grassland savannah site
Author: Venter, Marcell; Beukes, Johan Paul; van Zyl, Pieter Gideon; Vakkari, Ville; Virkkula, Aki; Josipovic, Miroslav; Kulmala, Markku; Laakso, Lauri
Contributor organization: Institute for Atmospheric and Earth System Research (INAR)
Department of Physics
Date: 2020-06-01
Language: eng
Number of pages: 17
Belongs to series: Atmospheric Environment
ISSN: 1352-2310
Abstract: Atmospheric aerosols have a significant effect on earth's radiative budget, particularly on regional scales. This paper presents a similar to 6 year, in situ, ground level aerosol scattering and absorption dataset, measured at a background site strategically positioned to enable differentiation of the effect of anthropogenic, population density and open biomass burning activities on a regional scale. Relatively well-defined seasonal and diurnal patterns were observed for all the aerosol optical properties, i.e. scattering coefficient (sigma(SP)), absorption coefficient (sigma(AP)), single scattering albedo (omega(0)) and Angstrom exponent of scattering (sigma(SP)). These patterns were explained by considering southern African specific sources and metrological conditions. Using a receptor modelling method (auto-generated source maps) it was found that air masses that had higher sigma(SP), sigma(AP) and omega(0), and lower alpha(SP), if compared with the relatively clean background, passed over source regions with significant industrial or other anthropogenic activities, higher population density, re-circulation of polluted air masses and higher open biomass burning frequency. To quantify differences, four source regions were defined, i.e. Karoo, Kalahari, anti-cyclonic recirculation pattern and the industrial hub of South Africa. Air masses that had passed over the Karoo source region represented the cleanest regional background conditions, while air masses that had passed either over the industrial hub and/or the anti-cyclonic recirculation pattern represented the most significant anthropogenically impacted, as indicated by the aerosol optical properties. The omega(0) medians of air masses that had passed over the Karoo (0.80-0.86) were 9, 12 and 7% lower than in air masses that had passed over source regions with the highest omega(0) median, in the warmest/wettest, coldest, and driest, peak open biomass burning periods, respectively.
Subject: Aerosol scattering coefficient (sigma(SP))
Absorption coefficient (sigma(AP))
Single scattering albedo (omega(0))
Angstrom exponent of scattering (alpha(SP))
Welgegund measurement station
114 Physical sciences
Peer reviewed: Yes
Rights: cc_by_nc_nd
Usage restriction: openAccess
Self-archived version: acceptedVersion

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