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Identification and Classification of Different Aerosol Types over a Subtropical Rural Site in Mpumalanga, South Africa: Seasonal Variations as Retrieved from the AERONET Sunphotometer

Category: Articles

Volume: 14 | Issue: 1 | Pages: 108-123
DOI: 10.4209/aaqr.2013.03.0079
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Kanike Raghavendra Kumar 1,2, Venkataraman Sivakumar1, Rajuru Ramakrishna Reddy3, Kotalo Rama Gopal3, Ayodele Joseph Adesina1

  • 1 Discipline of Physics, School of Chemistry and Physics, Westville Campus, University of KwaZulu–Natal, Durban 4000, KwaZulu-Natal, South Africa
  • 2 Now at Key Laboratory for Aerosol-Cloud-Precipitation of China Meteorological Administration, School of Atmospheric Physics, Nanjing University of Information Science and Technology, Nanjing 210044, Jiangsu, China
  • 3 Department of Physics, Aerosol and Atmospheric Research Laboratory, Sri Krishnadevaraya University, Anantapur 515 003, Andhra Pradesh, India

Abstract

This paper reports the observational results of aerosol optical characteristics, modification processes and discrimination of key aerosol types over Skukuza (24.9°S, 31.5°E, and 150 m), a subtropical rural site in South Africa (SA), using CIMEL Sunphotometer data, part of the AErosol RObotic NETwork (AERONET), from December 2005 to November 2006. The results show that a pronounced spectral and temporal variability in the optical properties of aerosols is mainly due to anthropogenic emissions. The discrimination of different aerosol types over Skukuza is also made using the daily mean values of aerosol optical depth at 500 nm (AOD500) and Ångström exponent (α440-870) by applying the threshold values. The results of the analysis indentified three individual components (biomass burning/urban (BU), desert dust (DD) and clean maritime (CM) aerosol types) of differing origin, composition and optical characteristics, and revealed that the percentage contribution of each of type of aerosol changed significantly from season to season. We also derived the curvature of a2 in an attempt to obtain information on aerosol-particle size and type, although the results revealed that the curvature alone is not enough to achieve this. In addition,, we analyzed the seasonal changes in aerosol characteristics using the classification scheme introduced in Gobbi et al. (2007) based on the measured scattering properties (α, dα) derived from the Sunphotometer data. The results show that during spring an extremely large fraction of fine-mode aerosols (η > 70%, Rf ~0.1 µm) in the turbid atmosphere was mainly caused by local anthropogenic pollution or biomass aerosol transported from forest fires. Whereas in summer, the low AOD (< 0.2) and smaller α (< 1.0) and η < 50% suggest the influence of transported mineral dust (coarse) over the region.

Keywords

AERONET Skukuza Optical properties Aerosol types Curvature


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