Characterisation of air masses passing over the Vredefort Dome world heritage site
In 2007, it was announced that the Vredefort Dome will be proclaimed South Africa’s seventh UNESCO (United Nations Educational, Scientific and Cultural Organisation) world heritage site. It is the largest and second oldest meteorite impact structure in the world and is situated in the Witwatersrand basin (containing ~40% of the world’s gold resources). In addition to the economic importance of the Vredefort Dome, it is of great geological (e.g. large meteorite crater with inverted sedimentary structures); cultural and historical (e.g. stone age caves with tools and human remains, Khoi-San rock art, remnants of the Anglo-Boer war and old gold mines); conservational (e.g. diverse indigenous plant, animal and bird species, as well as water quality associated with the Vaal river); and aesthetic (e.g. providing unique scenery with associated ecotourism opportunities) significance in South Africa. Air quality in the Vredefort Dome can potentially be affected by the nearby declared air pollution priority areas, i.e. the Vaal Triangle Airshed Priority Area (VTAPA), the Highveld Priority Area (HPA) and the Waterberg Priority Area (WPA), as well as the Johannesburg-Pretoria (Jhb-Pta) megacity, which is well-known for high levels of atmospheric pollution. Notwithstanding the national and international importance of the Vredefort Dome, as well as the proximity of the afore-mentioned polluted source regions, currently, no air quality data is available for this area. The management plan, as required by the UNESCO declaration, also highlighted this deficiency. In an effort to partially address the air quality knowledge gap, air masses from 1 June 2010 to 28 February 2014 passing over the Vredefort Dome were isolated and analysed at the Welgegund atmospheric measurement station as a proxy for ground-level air quality over the Vredefort Dome. Atmospheric species reported on in this thesis are in accordance with the National Ambient Air Quality Standards (NAAQS). The proxy method applied had some limitations, since the frequency of such back trajectories was limited and those that did comply passed mostly over the cleaner south-western sector from the Vredefort Dome. Additionally, dilution during transport and aging of air masses after passing over the Vredefort Dome before arriving at Welgegund could also affect the pollutant levels observed. By comparing the results with South African air quality standards, it is evident that O3 and PM10 exceeded the South African air quality standard limits. O3 is a regional problem, while PM10 mostly originates from industries, household combustion and savannah/grassland fires. Although there were no exceedances recorded for SO2 and NO2 in air masses complying with the selection criteria, it is highly likely that such exceedances will occur over the Vredefort Dome. It is suggested that emission interventions for industrial activities, the vehicular fleet, as well as savannah and grassland fires be done in order to address species of regional concern. In order to address household combustion emissions, social and economic transformations in South Africa need to be accomplished, which are linked to the economic success and -growth of the country.