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.

MSc., Faculty of Science, University of the Witwatersrand, 2011 / Atmospheric aerosols have direct and indirect impacts on the earth’s radiation budget and the radiative forcing on the climate system. A large uncertainty exists regarding aerosols and the effect they have on the earth’s radiation budget and global change. The distribution, concentration and types of aerosols are therefore of great importance regarding global warming and climate change. The purpose of this study is to present the atmospheric aerosol characteristics found over the South Atlantic, Southern Ocean and Antarctic continent as well as identify their origin. The aerosol optical properties over the South Atlantic and Southern Ocean region is analysed during the South African National Antarctic Expedition 2007/2008 (SANAE 47) take over cruise on board the M/V S.A. Agulhas. Very low aerosol optical thickness (AOT) values were obtained for the Antarctic Coastal region with a mean AOT500nm of 0.03 and a mean Angstrom exponent of 1.78. The South Atlantic region showed a mean AOT500nm of 0.06 and a mean Angstrom exponent of 0.72. AOT values for the South African coastal region had a mean AOT500nm of 0.07 and a mean Angstrom exponent of 0.76. Data comparisons confirm that the data acquired during the study are consistent with previous research from the study region. Comparisons were made between the dataset and the MODIS satellite aerosol product. A discrepancy was shown to exist between the MODIS aerosol product and the acquired dataset using the Microtops II Sunphotometer. Both MODIS TERRA and AQUA overestimate AOT at 550nm.

Aerosols are small, micrometer-sized particles, whose optical effects coupled with their impact on cloud properties is a source of large uncertainty in climate models. While their radiative forcing impact is largely of a cooling nature, there can be significant variations in the degree of their impact, depending on the size and the nature of the aerosols. The radiative and optical impact of aerosols are, first and foremost, dependent on their concentration or number density (an extensive parameter) and secondly on the size and nature of the aerosols (intensive, per particle, parameters). We employed passive (sunphotmetry) and active (backscatter lidar) measurements to retrieve extensive optical signals (aerosol optical depth or AOD and backscatter coefficient respectively) and semi-intensive optical signals (fine and coarse mode OD and fine and coarse mode backscatter coefficient respectively) and compared the optical coherency of these retrievals over a variety of aerosol and thin cloud events (pollution, dust, volcanic, smoke, thin cloud dominated). The retrievals were performed using an existing spectral deconvolution method applied to the sunphotometry data (SDA) and a new retrieval technique for the lidar based on a colour ratio thresholding technique. The validation of the lidar retrieval was accomplished by comparing the vertical integrations of the fine mode, coarse mode and total backscatter coefficients of the lidar with their sunphotometry analogues where lidar ratios (the intensive parameter required to transform backscatter coefficients into extinction coefficients) were (a) computed independently using the SDA retrievals for fine mode aerosols or prescribed for coarse mode aerosols and clouds or (b) computed by forcing the computed (fine, coarse and total) lidar ODs to be equal to their analog sunphotometry ODs. Comparisons between cases (a) and (b) as well as the semi-qualitative verification of the derived fine and coarse mode vertical profiles with the expected backscatter coefficient behavior of fine and coarse mode aerosols yielded satisfactory agreement (notably that the fine, coarse and total OD errors were <~ sunphotometry instrument errors). Comparisons between cases (a) and (b) also showed a degree of optical coherency between the fine mode lidar ratios.