RELATIONSHIP BETWEEN SURFACE, FREE TROPOSPHERIC AND TOTAL COLUMN OZONE IN 2 CONTRASTING AREAS IN SOUTH-AFRICA

Measurements of surface ozone in two contrasting areas of South Africa are compared with free tropospheric and Total Ozone Mapping Spectrometer (TOMS) total column ozone data. Cape Point is representative of a background monitoring station which is remote from pollution impacts, whereas the Eastern Transvaal Highveld (ETH) stations of Elandsfontein and Verkykkop are situated in an area of intense urban and industrial activity. At Cape Point the diurnal cycle in surface ozone is small, the seasonal cycle shows a winter maximum and a summer minimum. In contrast, the ETH stations show a spring maximum in surface ozone with evidence of a summer enhancement. Comparison with Cape Point data suggests that photochemical ozone production accounts for about 50% of the background value. Seasonal variations in total ozone are consistent over the whole of South Africa, indicating a cycle which is independent of varying surface ozone concentrations. The spring maximum in free tropospheric ozone (up to 12 km) over the interior of South Africa is thought to be due to long-range transport of biomass burn products from latitudes to the north, rather than the extension of a localised surface photochemical influence through the troposphere.