SO2 seasonal variation and assessment of Ozone Monitoring Instrument (OMI) measurements at Sharpeville (27.86°E; 26.68°S) a South African ground-based station

Abstract

In this study, seasonal, inter-annual variations of sulphur dioxide (SO2) were analysed for Sharpeville, South Africa (27.86°E; 26.68°S) for the period 2007–2013. Sharpeville is a residential site located within a highly industrialized region. Inter-annual variations were investigated by analysis of data collated by a ground-based (GB) instrument as well as the SO2 retrievals recorded by the Ozone Monitoring Instrument (OMI), a satellite-based sensor. The planetary boundary layer (PBL) SO2 vertical column data recorded by OMI were converted to surface SO2 volume mixing ratios using the pressure difference between surface and PBL. Accordingly, the OMI-derived SO2 measurements overestimated GB values and showed a good correlation with GB data in the austral winter. Besides this, the overall comparisons i.e. their daily, seasonal, and yearly correlation studies found that OMI-derived measurements was in better agreement with GB regardless of its moderate relative percentage of difference with GB. The seasonal variations of SO2 demonstrated that GB and OMI-derived measurements followed a general pattern of increasing trend from autumn until late winter and decreased from the onset of spring; however, the latter showed unique high SO2 levels in summer. Together with this, the inter-annual variations of both computations displayed a small decrement in SO2 values during the period 2011–2013. This however proved to be a stable variation when compared to other countries.