An overview of regional and local characteristics of aerosols in South Africa using satellite, ground, and modeling data

Abstract

We present a comprehensive overview of particulate air quality across the five major metropolitan areas of South Africa (Cape Town, Bloemfontein, Johannesburg and Tshwane (Gauteng Province), the Industrial Highveld Air Quality Priority Area (HVAPA), and Durban), based on a decadal (1 January 2000 to 31 December 2009) aerosol climatology from multiple satellite platforms and detailed analysis of ground-based data from 19 sites throughout Gauteng Province. Satellite analysis was based on aerosol optical depth (AOD) from MODIS Aqua and Terra (550 nm) and MISR (555 nm) platforms, Ångström Exponent (α) from MODIS Aqua (550/865 nm) and Terra (470/660 nm), ultraviolet aerosol index (UVAI) from TOMS, and results from the Goddard Ozone Chemistry Aerosol Radiation and Transport (GOCART) model. At continentally influenced sites, AOD, α, and UVAI reach maxima (0.12–0.20, 1.0–1.8, and 1.0–1.2, respectively) during austral spring (September–October), coinciding with a period of enhanced dust generation and the maximum integrated intensity of close-proximity and subtropical fires identified by MODIS Fire Information for Resource Management System (FIRMS). Minima in AOD, α, and UVAI occur during winter. Results from ground monitoring indicate that low-income township sites experience by far the worst particulate air quality in South Africa, with seasonally averaged PM10 concentrations as much as 136 % higher in townships that in industrial areas. We report poor agreement between satellite and ground aerosol measurements, with maximum surface aerosol concentrations coinciding with minima in AOD, α, and UVAI. This result suggests that remotely sensed data are not an appropriate surrogate for ground air quality in metropolitan South Africa.

Aerosol-Cloud-Precipitation Interactions over Major Cities in South Africa: Impact on Regional Environment and Climate Change

“…In terms of temporal variation, the mean AOD 550 for the study period (2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)) is noticed to be the lowest at Bloemfontein 0.06 ± 0.04 followed by Cape Town 0.08 ± 0.02, then Potchefstroom 0.09 ± 0.05; Pretoria and Skukuza had 0.11 ± 0.05 each and with the highest observed at Durban 0.13 ± 0.05. This result is in good agreement with Hersey et al (2015) examined on tropospheric aerosol loading over different environments of SA. Monthly and seasonal variations of AOD 550 which is shown in Table 2 can be clearly seen in all the six locations.…”

“…These locations are diverse in population, climate and topographic variation; make SA geographically unique for any study of spatio-temporal patterns. The description of each region was described by several earlier researchers (Adesina et al, 2010;Sivakumar et al, 2010;Queface et al, 2011;Kumar et al, 2013;Adesina et al, 2014;Kumar et al, 2014;Hersey et al, 2015). …”

“…The lowest value (AOD 550 < 0.1) of the spatial variation of AOD 550 for the period 2004-2013 is observed over Bloemfontein, which is in the Free State province lies is in the heart of SA, with the grassland, crop fields and sandstone mountains hosting the country's largest gold mining complex. AOD 550 ranging between 0.10 and 0.13 is found over four locations; Potchefstroom in the North-West province with mostly flat areas of scattered trees and grassland, Skukuza in the Mpumalanga province with high altitude grassland and accounting for about 83% of SA's coal production (Hersey et al, 2015), Cape Town in the Western Cape province having an exceptional topographical and vegetation diversity Hersey et al, 2015) and Pretoria in the Gauteng province containing the country's largest city making it the province with the highest population density and urbanization . While Durban in the Kwazulu-Natal province has three geographical regions of lowland, midland and plateau with the surrounding coastal region having subtropical forest has the highest AOD 550 close to 0.2.…”

“…Although many researchers have carried out investigations on the aerosol optical depth (AOD) over some parts or the whole of South Africa (SA) using both ground-based instruments (Kumar et al, 2013 and references therein; Adesina et al, 2014;Hersey et al, 2015) and satellite-based instruments (Tesfaye et al, 2011;Kumar et al, 2014), but aerosol-cloud-precipitation interactions has not been reported to the best of our knowledge. A number of studies have been conducted to address the spatial and temporal variability of aerosols and clouds and its impact on rainfall (e.g., Alam et al, 2010;Balakrishnaiah et al, 2012;Alam et al, 2014;Kang et al, 2015 and references therein).…”

A Geostationary Air Quality Monitoring Platform for Africa

“…In Africa surface observations of atmospheric composition are sparse, environmental legislation is limited to a few countries, and only South Africa has welldefined standards and a widespread monitoring network (Kgabi, 2012). Still, successful environmental policy in South Africa is hindered by non-compliance (Groundwork, 2014), data gaps, and variable data quality (Hersey et al, 2015).…”