Aerosol loading over the South African Highveld
Date
2009-03-31T05:16:48Z
Authors
Bigala, Thomas Aquinas
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Abstract
The Highveld region of South Africa contributes substantially to the aerosol loading
over southern Africa because of its importance as an industrial, mining and farming
base. Aerosols affect climate by absorbing or reflecting incoming solar radiation, and
by affecting cloud microphysics, cloud albedo and precipitation. The physical and
optical properties of industrial/urban aerosols over the Highveld region of
South Africa were analysed during a 32-day winter sampling period (21 May to
21 June) in 2002; a 32-day summer sampling period (21 October to 21 November) in
2002, and a second 32-day winter sampling period (19 May to 19 June) in 2003.
Synoptic circulation systems were examined in as far as they affect the horizontal
transport of aerosols over the Highveld region. Measurements of aerosol optical
thickness (AOT) from the ground to the top of the atmosphere and aerosol size
distribution characteristics over the Highveld region were taken using hand-held
hazemeters and a CIMEL sun photometer. The AOT observed over the region during
the winter 2002 and 2003 sampling periods and during the summer 2002 sampling
period indicated high turbidity. In the 2002 winter sampling period, the AOT530nm
ranged between 0.05 to 0.7 with an average of 0.14. In the 2002 summer sampling
period, the AOT530nm ranged between 0.05 to 0.6, with an average of 0.24. In the
2003 winter sampling period, the AOT500nm ranged between 0.06 to 0.6, with an
average of 0.21. The Ångström exponent value had a wide range, 0.8 to 2.4 in the 2002 winter and summer sampling periods and also in the 2003 winter sampling
period, indicating that a range of particle sizes was present over the Highveld region.
The Ångström exponent values obtained were derived from the influences of Aeolian
dust, coarse-mode industrial particles and, to a small extent, fine-mode biomassburning
aerosols. Case studies, based on trajectory analysis and meteorology of the
sampling area, were made of the aerosols emanating from the township sites during
each of the three sampling periods to observe the build-up and dispersion of aerosols
at that time.
Description
Keywords
Aerosol loading, hand-held hazemeter, CIMEL sun photometer, Angstrom exponent values, aerosol optical thickness values