Abstract
The quality of air breathed in South Africa is of great concern, especially in industrialised regions where PM2.5 concentrations are high. Long term exposure to PM2.5 is associated with serious adverse health impacts. Traditionally, PM2.5 is monitored by a network of ground-based instruments. However, the coverage of monitoring networks in South Africa is not dense enough to fully capture the spatial variability of PM2.5 concentrations. This study explored whether satellite remote sensing could offer a viable alternative to ground-based monitoring. Using an eight-year record (2009 to 2016) of satellite retrievals (MODIS, MISR and SeaWIFS) for PM2.5 concentrations, spatial variations and temporal trends for PM2.5 are evaluated for the Vaal Triangle Airshed Priority Area (VTAPA). Results are compared to corresponding measurements from the VTAPA surface monitoring stations. High PM2.5 concentrations were clustered around the centre and towards the south-west of the VTAPA over the highly industrialised cities of Vanderbijlpark and Sasolburg. Satellite retrievals tended to overestimate PM2.5 concentrations. Overall, there was a poor spatial agreement between satellite-retrieved PM2.5 estimates and ground-level PM2.5 measurements. Root mean square error values ranged from 6 to 11 µg/m3 and from -0.89 to 0.32 for the correlation coefficient. For satellite remote sensing to be effectively exploited for air quality assessments in the VTAPA and elsewhere, further research to improve the precision and accuracy of satellite-retrieved PM2.5 is required.
Highlights
At a global scale, air pollution is ranked fourth amongst the leading risk factors to human health, with recent estimates linking it to over 5 million premature deaths (Mannucci and Franchini, 2017; Bhanarkar et al, 2018; Health Effects Institute, 2019)
It can be observed that in most cases, there was an overestimation of observed PM2.5 concentrations by the satellite retrievals, with the exception for the Kliprivier and Sebokeng stations, where ground measurements were much higher than the satellite-retrieved estimates
Both satellite retrievals and ground measurements showed that PM2.5 concentrations for all sites, except Diepkloof, were above the annual National Ambient Air Quality Standards (NAAQS)
Summary
Air pollution is ranked fourth amongst the leading risk factors to human health, with recent estimates linking it to over 5 million premature deaths (Mannucci and Franchini, 2017; Bhanarkar et al, 2018; Health Effects Institute, 2019). In sub-Saharan Africa (SSA), in the urban areas, the deterioration in air quality as a result of rapid urbanisation, population growth and industrial expansion is evident (Amegah and Agyei-Mensah, 2017; Fayiga, Ipinmoroti and Chirenje, 2018). In South Africa, air pollution has become an important issue, especially in industrialised regions like the Vaal Triangle Airshed Priority Area (VTAPA) where strong economic growth has taken place (Naiker et al, 2012; Zhu et al, 2012). The VTAPA routinely experiences poor air quality as a result of strong emissions from industries, residential burning, vehicles and fugitive dust sources coupled with unfavourable meteorological conditions that have led to the accumulation of PM2.5 in high concentrations (Annegarn and Scorgie, 1997; Scorgie et al, 2003)
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