Quantitative comparison of the aerosol optical properties over Durban using ground and satellite based instrumentation.
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2017
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Abstract
Aerosols are ubiquitous constituents in the atmosphere and are important for atmospheric processes. This is due to their ability to scatter and absorb solar radiation and influence cloud microphysics. This study will focus on discerning trends in aerosol optical properties in Durban (29.8587° S, 31.0218° E), a coastal city on the east coast of South Africa, using the preliminary results from the sun-photometer located at the University of KwaZulu-Natal. These results will also be compared to the well-established Skukuza sun-photometer. Skukuza is a rural agricultural area in the north eastern parts of South Africa. The Aerosol Optical Depth (AOD), Angstrom Exponent (α440–870), Columnar Water Vapour (CWV), Volume Size Distribution (VSD), Single Scattering Albedo (SSA), Asymmetry parameter (ASP), Real and Imaginary parts of the complex refractive index were studied for Durban and Skukuza. Analysis of the aerosol optical properties suggested that various sources of aerosols were identified for Durban, such as biomass burning, urban industrial aerosols and marine aerosols. Biomass burning aerosols impacted Skukuza during spring. There was a high extent of fine mode aerosols present throughout the year for Skukuza, indicating that urban industrial emissions from the South African Highveld region can also contribute to aerosol loads in the region.
Preliminary results from the ground-based Durban sun-photometer was used to compare aerosol optical depth at 550 nm (AOD) to the satellite Moderate Resolution Imaging Spectroradiometer (MODIS) for the Aqua, Terra and Aqua and Terra combined (average of both) datasets for the dark target (DT) and deep blue (DB) retrieval algorithms to validate satellite retrievals. The results gave way to moderate correlations between MODIS Terra and the Durban sun-photometer for both DB (R2 = 0.70) and DT (R2 = 0.60), and between MODIS Aqua and the Durban sun-photometer for DB (0.68). Good correlations were observed for MODIS Terra and Aqua merged for both DB (0.79) and DT (0.74). The ability of MODIS to predict AOD was noted as dependent on the season and location.
HYSPLIT 720 hour–backward trajectory analysis, AOD and α440–870 from the Durban sun-photometer, a Lidar profile and satellite imagery were used to determine if air mass from the Calbuco volcanic eruption in Chile in April 2015 reached Durban. Trajectory analysis found that only during May 2015, was air masses arriving from South America, within the 20 km altitude. This led to the assumption that stratospheric aerosols from the Calbuco volcano, travelled to Durban. Analysis of the AOD found that only during 2015 was a constant phenomenon driving AOD in Durban and this was attributed to the eruption. Lidar observations coupled with the backward trajectory analysis allowed for the identification of air masses in Durban arriving from the Calbuco volcano in Chile.
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Master of Science in Environmental Science. University of KwaZulu-Natal, Durban 2017.