Long-term trends of atmospheric SO2, NO2 and O3 concentrations at South African INDAAF sites

Abstract

South Africa is an important source region of atmospheric pollutants, which is compounded by high population- and industrial growth. However, this region is understudied, especially with regard to evaluating long-term trends of atmospheric pollutants. In this study statistical modelling of SO2, NO2 and O3 long-term trends based on 21-, 19- and 16-year passive sampling datasets available for three South African INDAAF (International network to study Atmospheric Chemistry and Deposition in Africa) sites, which are regionally representative of the industrialised north-eastern interior were conducted. The interdependencies between local, regional and global parameters on SO2, NO2 and O3 levels were investigated. Long-term temporal trends indicated temporal variability at all three sites, which could be ascribed to changes in meteorology and/or variances in sources. Local, regional and global parameters contributed to SO2 variability, with total solar irradiation being the most significant factor at the regional background site, Louis Trichardt (LT). Temperature was the most important factor at Skukuza (SK), located in the Kruger National Park, while population growth (P) made the most substantial contribution at the industrially impacted Amersfoort (AF) site. Air masses passing over the source region also contributed to SO2 levels at SK and LT. Local and regional factors made more substantial contributions to modelled NO2 levels, with P being the most significant factor explaining NO2 variability at all three sites, while relative humidity was the most important meteorological factor. The important contribution of P on modelled SO2 and NO2 concentrations was indicative of the impact of increased anthropogenic activities and energy demand in South Africa. ENSO made a significant contribution to modelled O3 levels at all three sites, while the influence of local and regional meteorological factors was also evident. Trend lines for SO2 and NO2 at AF indicated an increase in SO2 and NO2 concentrations over the 19-year sampling period, while an upward trend in NO2 levels at SK signified the influence of growing rural communities. O3 remained relatively constant at all three sites