Spring-time ozone and solar ultraviolet radiation variations over the Western Cape, South Africa

Abstract

The anti-correlation between solar ultraviolet radiation (UV) and atmospheric ozone is well understood. Around the world, decreased ozone concentrations have been recorded which lead to increased solar UV radiation levels at the surface. These increased levels of solar UV radiation have potentially negative impacts on public health. The study was done to determine if the break-up of the Antarctic ozone hole during austral spring has an impact on the stratospheric columnar ozone (SCO) concentrations and resulting ambient solar UV-B radiation levels at two sites in the Western Cape, South Africa. There were five objectives:1) Determine the climatology of solar UV-B radiation as well as the climatology of TOC and SCO for Cape Point and Cape Town; 2) Determine clear-sky days for Cape Point and Cape Town and then analyse the anti-correlation between solar UV-B radiation and TOC, and solar UV-B radiation and SCO on the identified clear-sky days; 3) Identify low TOC and SCO events at Cape Point and Cape Town focusing on spring and summer months; 4) Use appropriate models to determine the origin of ozone-poor air parcels observed during low ozone events that occur at Cape Point and Cape Town; 5) Demonstrate whether or not Antarctic ozone hole events influence ozone at Cape Point and Cape Town. The solar UV-B radiation climatologies showed that solar UV radiation was at a maximum during December and January at Cape Point and Cape Town. At Cape Point the strongest anti-correlation on clear-sky days was found at SZA 20° linear fit correlation coefficient of -0.838 and -0.804 for total ozone column (TOC) and SCO respectively with a corresponding exponential fit R2 value of 0.710 and 0.664. An average radiation amplification factor of 0.916 was found for Cape Point. The largest decrease in ozone concentrations were found to have occurred during September months. Investigating the source of ozone-poor air, HYSPLIT and MIMIOSA-CHIM models showed that polar vortex has a limited effect on ozone concentrations at 435 - 440 K for September and 600 K for November at both sites. It was seen that tropical air masses more frequently effect the study area and this requires further investigation.