Measurement report: Statistical modelling of long-term trends of atmospheric inorganic gaseous species within proximity of the pollution hotspot in South Africa

• Main Authors: J.-S. Swartz, P. G. van Zyl, J. P. Beukes, C. Galy-Lacaux, A. Ramandh, J. J. Pienaar
• Format: Article
• Language: English
• Published: Copernicus Publications 2020-09-01
• Series: Atmospheric Chemistry and Physics
• Online Access: https://acp.copernicus.org/articles/20/10637/2020/acp-20-10637-2020.pdf
• ISSN: 1680-7316; 1680-7324

<p>South Africa is considered 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. The aim of this study was to perform statistical modelling of <span class="inline-formula">SO₂</span>, <span class="inline-formula">NO₂</span> and <span class="inline-formula">O₃</span> long-term trends based on 21-, 19- and 16-year passive sampling datasets available for three South African INDAAF (International Network to study Deposition and Atmospheric Chemistry in Africa) sites located within proximity of the pollution hotspot in the industrialized north-eastern interior in South Africa. The interdependencies between local, regional and global parameters on variances in <span class="inline-formula">SO₂</span>, <span class="inline-formula">NO₂</span> and <span class="inline-formula">O₃</span> levels were investigated in the model. Average monthly <span class="inline-formula">SO₂</span> concentrations at Amersfoort (AF), Louis Trichardt (LT) and Skukuza (SK) were 9.91, 1.70 and 2.07&thinsp;<span class="inline-formula">µ</span>g&thinsp;m<span class="inline-formula">⁻³</span>, respectively, while respective mean monthly <span class="inline-formula">NO₂</span> concentrations at each of these sites were 6.56, 1.46 and 2.54&thinsp;<span class="inline-formula">µ</span>g&thinsp;m<span class="inline-formula">⁻³</span>. Average monthly <span class="inline-formula">O₃</span> concentrations were 50.77, 58.44 and 43.36&thinsp;<span class="inline-formula">µ</span>g&thinsp;m<span class="inline-formula">⁻³</span> at AF, LT and SK, respectively. Long-term temporal trends indicated seasonal and inter-annual variability at all three sites, which could be ascribed to changes in meteorological conditions and/or variances in source contribution. Local, regional and global parameters contributed to <span class="inline-formula">SO₂</span> variability, with total solar irradiation (TSI) being the most significant factor at the regional background site LT. Temperature (<span class="inline-formula"><i>T</i></span>) was the most important factor at SK, located in the Kruger National Park, while population growth (<span class="inline-formula"><i>P</i></span>) made the most substantial contribution at the industrially impacted AF site. Air masses passing over the source region also contributed to <span class="inline-formula">SO₂</span> levels at SK and LT. Local and regional factors made more substantial contributions to modelled <span class="inline-formula">NO₂</span> levels, with <span class="inline-formula"><i>P</i></span> being the most significant factor explaining <span class="inline-formula">NO₂</span> variability at all three sites, while relative humidity (RH) was the most important local and regional meteorological factor. The important contribution of <span class="inline-formula"><i>P</i></span> on modelled <span class="inline-formula">SO₂</span> and <span class="inline-formula">NO₂</span> concentrations was indicative of the impact of increased anthropogenic activities and energy demand in the north-eastern interior of South Africa. Higher <span class="inline-formula">SO₂</span> concentrations, associated with lower temperatures, as well as the negative correlation of <span class="inline-formula">NO₂</span> levels to RH, reflected the influence of pollution build-up and increased household combustion during winter. The El Niño–Southern Oscillation (ENSO) made a significant contribution to modelled <span class="inline-formula">O₃</span> levels at all three sites, while the influence of local and regional meteorological factors was also evident. Trend lines for <span class="inline-formula">SO₂</span> and <span class="inline-formula">NO₂</span> at AF indicated an increase in <span class="inline-formula">SO₂</span> and <span class="inline-formula">NO₂</span> concentrations over the 19-year sampling period, while an upward trend in <span class="inline-formula">NO₂</span> levels at SK signified the influence of growing rural communities. Marginal trends were observed for <span class="inline-formula">SO₂</span> at SK, as well as <span class="inline-formula">SO₂</span> and <span class="inline-formula">NO₂</span> at LT, while <span class="inline-formula">O₃</span> remained relatively constant at all three sites. <span class="inline-formula">SO₂</span> and <span class="inline-formula">NO₂</span> concentrations were higher at AF, while the regional <span class="inline-formula">O₃</span> problem was evident at all three sites.</p>