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Previous research has shown that there is considerable enhancement of tropospheric ozone over the African continent. The role of biomass burning as a source of ozone precursor gases and the atmospheric circulation, in particular the anticyclonic gyres over southern Africa, are known to be important in the accumulation of ozone over the subcontinent. In addition, the injection of ozone-rich air from the stratosphere is known to account for the occurrence of ozone peaks in the upper troposphere. This thesis is aimed at investigating the occurrence of high ozone events, defined as 2::100 ppbv, over Africa. Their variability in time (seasonal distribution) and space (latitudinal distribution) is quantified for the upper tropospheric region (~l 0 - 12 km) from 35°N to approximately 35°S . The data used are part of the MOZAIC (Measurement of OZone and wAter vapour by Airbus In-service airCraft) database. Ozone, water vapour. and temperature are measured at cruise altitude by these in-service aircraft, and this study explores data gathered on flights between Europe and Africa over the period January 1996 to December 1998. Complementary data from the European Centre for Medium Range Weather Forecasts (ECMWF) and satellite images are used to investigate case studies for selected flights in order to determine the origin of ozone episodes. Backward trajectory modeling is used to determine the source of air masses possibly related to ozone episodes. Correspondence with high potential vorticity and low water vapour content are used as stratospheric tracers and are indicative of stratospheric-tropospheric injection. Marked seasonal and latitudinal differences in the frequency and nature of ozone episodes are noted between the northern and southern latitudes. The seasonal variation of ozone episodes is more prominent in the extratropics than in the tropics. The highest frequencies are observed in the Northern Hemisphere to the north of 200N in spring and summer, and in the Southern Hemisphere to the south of 30°8 in winter and spring . Between these latitudes the distribution of peaks is sparse. An exception is observed during the austral spring when a relatively high number of peaks south of the equator is evident. The spring frequency peak is common to both hemispheres and is likely to result from a biomass burning influence, and stratospheric ozone injection into the troposphere during this season. Ozone peaks north of 15°N are greater in magnitude (up to 350 ppbv) than those in the tropics and in the Southern Hemisphere, where peaks do not exceed 200 ppbv. The horizontal extent of the ozone events ranged from a few tens of kilometers to over 1000 km in the boreal spring, although they seldom exceeded 100 km in the tropics. Two case studies were examined in detail. In the first case study, ozone peaks up to 180 ppbv were observed at approximately 12° S in the summer. They ranged between 3.5 and 21 km in horizontal extent and were accompanied by increased relative humidity and evidence of uplift. They were attributed to localized biomass burning and subsequent convective uplift to the upper troposphere. The possibility of enhancement due to convective uplift and lightning production was discussed. The second case study, in which an ozone peak of 287 ppbv was observed at approximately 31°S in springtime, had a horizontal extent of 840 km and was accompanied by low relative humidity values and high potential vorticity, indicative of air of stratospheric origin. / Thesis (M.Sc.)-University of Natal, Durban, 2002.

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Networks of ground-based and satellite borne instruments to measure ultraviolet (UV) sunlight and total column ozone have greatly contributed to an understanding of increased amounts of UV reaching the surface of the Earth caused by stratospheric ozone depletion. Increased UV radiation has important potential effects on human health, and agricultural and ecological systems. Observations from these networks make it possible to monitor total ozone decreases and to predict ozone recovery trends due to global efforts to curb the use of products releasing chemicals harmful to the ozone layer. Thus, continued and expanded global monitoring of ozone and UV is needed. However, existing automatic stratospheric ozone monitors are complex and expensive instruments. The main objective of this research was the development of a low-cost fully automated total column ozone monitoring instrument which, because of its affordability, will increase the number of instruments available for ground-based observations. The new instrument is based on a high-resolution fiber optic spectrometer, coupled with fiber optics that are precisely aimed by a pan and tilt positioning mechanism and with controlling programs written in commonly available software platforms which run on a personal computer. This project makes use of novel low-cost fiber optic spectrometer technology. A cost advantage is gained over available units by placing one end of the fiber outdoors to collect sunlight and convey it indoors, thereby allowing the spectrometer and computer to be placed in a controlled environment. This reduces the cost of weatherproofing and thermal compensation. Cost savings also result from a simplified sun targeting system, because only a small pan and tilt device is required to aim the lightweight fiber optic ends. Precision sun-targeting algorithms, optical filter selection, and software to derive ozone from spectral measurements by the spectrometer are a major contribution of this project. This system is a flexible platform which may be adapted to study other atmospheric constituents such as sulfur dioxide, nitrous oxides, and haze.

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