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 Angstrom 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.
Highlights
Atmospheric aerosols are solid or liquid particles suspended in the air
The results showed a large temporal variation of the examined aerosol properties (AOD500, α440-870, and a2) over Skukuza strongly affected by the continents, the outflow of pollutants, relative humidity and the mixing processes in the rural atmosphere as it has been already reported by the same authors in their recent works
Using the relationship between AOD500 and α440-870, four aerosol types were identified over Skukuza region in order to represent different atmospheric conditions (i.e., biomass burning/urban-industrial (BU), clean maritime (CM) and desert dust (DD) aerosols)
Summary
Atmospheric aerosols are solid or liquid particles suspended in the air. They have significance at local, regional and global scales and have received prominent attention in the past few years (Penner et al, 1994; Seinfeld and Pandis, 2006). The climatic and environmental effects of atmospheric aerosols are the critical issues in global science community because aerosols, derived from natural and anthropogenic emission sources, are well known to affect the air quality, human health, and radiation budget (IPCC, 2007, Srivastava et al, 2012). Uncertainty in quantifying the climatic impacts of aerosols continues to be greater than that of greenhouse gases (IPCC, 2007) due to variety of their sources, varying trends in aerosol loading and extreme heterogeneity in the spatial and temporal variability of their optical and microphysical properties (Morgan et al, 2006; Kaskaoutis et al, 2010).
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