NITROGEN OXIDES ON THE SOUTH AFRICAN HIGHVELD

Abstract

Satellite retrievals have highlighted the South African Highveld as a region with one of the highest nitrogen oxide (NOx) emission densities in the world. There are numerous sources of NOx on the Highveld, including coal-fired power stations, petrochemical and other industries, motor vehicles and lightning, but surface measurements of NOx have not indicated that there is any cause for concern. A number of research initiatives are being undertaken in an attempt to resolve the discrepancy between surface measurements and satellite retrievals of NOx. An assessment of ground-level concentrations in various environments, including industrial and urban regions, has shown that NOx levels recorded in the low-income urban area are significantly higher than those recorded downwind of industries or power stations. NO2 column densities have been remotely sensed over the Highveld using an airborne imaging Differential
Optical Absorption Spectrometer (iDOAS), in order to validate the satellite retrievals and investigate individual sources of NOx. Results from the first campaign show high NO2 integrated column densities in the immediate vicinity of sources. Well defined plumes can be observed downwind of prominent sources.