Changes in surface solar ultraviolet (UV) radiation related to changes in atmospheric conditions over South Africa

• Main Author: Du Preez, David Jean
• Other Authors: Laboratoire de l'Atmosphère et des Cyclones (LACy), Institut national des sciences de l'Univers (INSU - CNRS)-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS)-Météo-France, Université de la Réunion, University of Pretoria, Hassan Benchérif, Caradee Wright
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2021
• Subjects: Aerosols; Ozone; UV radiation; Atmosphere; Aérosols; Radiations UV; Atmosphère; [PHYS.PHYS.PHYS-AO-PH]Physics [physics]/Physics [physics]/Atmospheric and Oceanic Physics [physics.ao-ph]; Antarctic; Austral; The Antarctic; Antarc*
• Online Access: https://theses.hal.science/tel-03662624; https://theses.hal.science/tel-03662624/document; https://theses.hal.science/tel-03662624/file/2021LARE0020_D_DU_PREEZ.pdf

Solar ultraviolet radiation (UVR) that reaches the surface of the Earth varies due to changes in atmospheric parameters such as cloud cover, ozone and aerosol concentrations. Personal exposure to excessive solar UVR has significant health implications for the human population including the development of skin cancers and certain cataracts. The research presented in this thesis aimed to quantify the effects of aerosols and ozone on surface UVR as well as to estimate the keratinocyte cancer risk posed to the public due to the exposure to solar UVR. Stratospheric ozone is the most important atmospheric constituent for the absorption of incoming solar UVR. The annual formation of the Antarctic ozone hole has beenfound to affect stratospheric ozone levels around the Southern Hemisphere and result in increased UVR at the surface due to the passage of the polar vortex in the austral spring and summer. The radiative effect of aerosols from volcanic eruptionsand biomass burning can significantly affect surface solar UVR levels. The effects of volcanic eruptions and biomass burning may not be limited to the source region but can be observed thousands of kilometres away. Examining low-ozone events that occurred during the spring and summer months at Cape Point in South Africa, the origins of ozone poor-air masses were determined using a dynamical transport model. The origins of ozone-poor air masses at Cape Point were found to be mainly from sub-tropical regions in the lower stratosphere (435 K – 485 K) and rarely from the polar vortex in the high stratosphere (600 K). Furthermore, these low-ozone events contributed to increased surface UVR on clear-sky days. Investigating the effect of aerosols from a volcanic eruption and biomass burning, indicated that volcanic eruptions could affect the aerosol loading at a distant secondary location. Increases in the aerosol loading could be attributed to the dispersion on the plume which was modelled with a dispersion model and observations from satellites. Using a radiative transfer ...