Source apportionment of ambient PM10−2.5 and PM2.5 for the Vaal Triangle, South Africa

The Vaal Triangle Airshed Priority Area (VTAPA), like other priority areas in South Africa, has an air pollution problem. Understanding the sources contributing to air pollution in this priority area will assist in the selection and implementation of appropriate control strategies. For this study, aerosol samples in the coarse (PM10-2.5) and fine (PM2.5) fraction were collected at four sites in the VTAPA during summer/autumn, winter, and spring. The contributing sources were identified and characterised based on the elemental and ionic compositions obtained through X-ray fluorescence and ion chromatography analysis. The highest seasonal median concentrations of PM10-2.5 (116 μg/m3) and PM2.5 (88 μg/m3) were observed in Sharpeville during the winter. The lowest median concentrations of PM10-2.5 (25 μg/m3) and PM2.5 (18 μg/m3) were detected in Zamdela during the summer/autumn period. At all sites, there was a high abundance of crustal elements in PM10-2.5 and a dominance of coal and biomass combustion-related elements in PM2.5. The Positive Matrix Factorisation receptor model identified dust-related and secondary aerosols as the major contributing sources of PM10-2.5. PM2.5 contributions were predominantly from coal burning for Sebokeng and Sharpeville and from industry, wood and biomass burning, and secondary aerosols for Kliprivier and Zamdela. The results of this study identify the main sources contributing to particulate air pollution in the VTAPA and provide local authorities with valuable information for decision-making.Significance: Dust, industry, domestic coal burning, vehicles, and wood and biomass combustion are the key sources of particulate air pollution in the VTAPA that need to be prioritised by decision-makers. Although Sebokeng and Sharpeville are located within the vicinity of industries, domestic coal burning has a greater contribution to particulate loading at these sites. Results from this study will assist in the design of local municipality air quality management plans for the VTAPA

Size-resolved characteristics of inorganic ionic species in atmospheric aerosols at a regional background site on the South African Highveld

Aerosols consist of organic and inorganic species, and the composition and concentration of these species depends on their sources, chemical transformation and sinks. In this study an assessment of major inorganic ions determined in three aerosol particle size ranges collected for 1year at Welgegund in South Africa was conducted. SO42- and ammonium (NH4+) dominated the PM1 size fraction, while SO42- and nitrate (NO3) dominated the PM1-2.5 and PM2.5-10 size fractions. SO42- had the highest contribution in the two smaller size fractions, while NO3- had the highest contribution in the PM2.5-10 size fraction. SO42- and NO3- levels were attributed to the impacts of aged air masses passing over major anthropogenic source regions. Comparison of inorganic ion concentrations to levels thereof within a source region influencing Welgegund, indicated higher levels of most species within the source region. However, the comparative ratio of SO42- was significantly lower due to SO42- being formed distant from SO2 emissions and submicron SO42- having longer atmospheric residencies. The PM at Welgegund was determined to be acidic, mainly due to high concentrations of SO42-. PM1 and PM1-2.5 fractions revealed a seasonal pattern, with higher inorganic ion concentrations measured from May to September. Higher concentrations were attributed to decreased wet removal, more pronounced inversion layers trapping pollutants, and increases in household combustion and wild fires during winter. Back trajectory analysis also revealed higher concentrations of inorganic ionic species corresponding to air mass movements over anthropogenic source regions.Peer reviewe

Size-resolved characteristics of inorganic ionic species in atmospheric aerosols at a regional background site on the South African Highveld

Aerosols consist of organic and inorganic species, and the composition and concentration of these species depends on their sources, chemical transformation and sinks. In this study an assessment of major inorganic ions determined in three aerosol particle size ranges collected for 1year at Welgegund in South Africa was conducted. SO42- and ammonium (NH4+) dominated the PM1 size fraction, while SO42- and nitrate (NO3) dominated the PM1-2.5 and PM2.5-10 size fractions. SO42- had the highest contribution in the two smaller size fractions, while NO3- had the highest contribution in the PM2.5-10 size fraction. SO42- and NO3- levels were attributed to the impacts of aged air masses passing over major anthropogenic source regions. Comparison of inorganic ion concentrations to levels thereof within a source region influencing Welgegund, indicated higher levels of most species within the source region. However, the comparative ratio of SO42- was significantly lower due to SO42- being formed distant from SO2 emissions and submicron SO42- having longer atmospheric residencies. The PM at Welgegund was determined to be acidic, mainly due to high concentrations of SO42-. PM1 and PM1-2.5 fractions revealed a seasonal pattern, with higher inorganic ion concentrations measured from May to September. Higher concentrations were attributed to decreased wet removal, more pronounced inversion layers trapping pollutants, and increases in household combustion and wild fires during winter. Back trajectory analysis also revealed higher concentrations of inorganic ionic species corresponding to air mass movements over anthropogenic source regions.Peer reviewe

Assessment of polar organic aerosols at a regional background site in southern Africa

A recent paper reported GCxGC-TOFMS analysis used for the first time in southern Africa to tentatively characterise and semi-quantify 1000 organic compounds in aerosols at Welgegund - a regional background atmospheric monitoring station. Ambient polar organic aerosols characterised are further explored in terms of temporal variations, as well as the influence of meteorology and sources. No distinct seasonal pattern was observed for the total number of polar organic compounds tentatively characterised and their corresponding semi-quantified concentrations (sum of the normalised response factors, Sigma NRFs). However, the total number of polar organic compounds and Sigma NRFs between late spring and early autumn seemed relatively lower compared to the period from mid-autumn to mid-winter, while there was a period during late winter and early spring with significantly lower total number of polar organic compounds and Sigma NRFs. Relatively lower total number of polar organic compounds and corresponding Sigma NRFs were associated with fresher plumes from a source region relatively close to Welgegund. Meteorological parameters indicated that wet removal during late spring to early autumn also contributed to lower total numbers of polar organics and associated Sigma NRFs. Increased anticyclonic recirculation and more pronounced inversion layers contributed to higher total numbers of polar organic species and Sigma NRFs from mid-autumn to mid-winter, while the influence of regional biomass burning during this period was also evident. The period with significantly lower total number of polar organic compounds and Sigma NRFs was attributed to fresh open biomass burning plumes occurring within proximity of Welgegund, consisting mainly of volatile organic compounds and non-polar hydrocarbons. Multiple linear regression substantiated that the temporal variations in polar organic compounds were related to a combination of the factors investigated in this study.Peer reviewe

Assessing SO2, NO2 and O3 in rural areas of the North West Province

Publisher Copyright: © 2021 The Author(s). Published under a Creative Commons Attribution Licence. All Rights Reserved.Air quality monitoring has been lacking in the rural and western North West Province. Here ambient sulphur dioxide (SO2), nitrogen dioxide (NO2) and ozone (O3) concentrations, monitored with passive samplers at 10 sites, are presented. Widespread SO2 and NO2 problems weren't observed. However, regular O3 standard limit exceedances are likely across the province. Increased SO2 and NO2 concentrations in the colder and drier months were evident. Inversion layer trapping of low-level emissions during the colder months and open biomass burning in the drier months increased ground level pollutant concentrations. Wet deposition of SO2 and NO2, and enhanced SO2 conversion to particulate sulphate, result in lower wet season concentrations. O3 concentrations were lower from May to July and higher from August to March. Three phenomena contributed to this. Firstly, shorter daylight hours (less photochemistry) and secondly, lower biogenic volatile organic compound (O3 precursors) concentrations during the colder months. Thirdly, the late winter/ early spring open biomass burning peak lead to elevated carbon monoxide (CO) concentration (also an O3 precursor). Spatial patterns indicated higher SO2 concentrations in the west, due mainly to industrial emissions. The NO2 spatial map indicated two areas of higher concentration, i.e. Bapong in the east due mainly to industrial emissions, and Taung with its higher population density. The O3 spatial map was almost the inverse of NO2. The lower O3 and higher NO2 around Taung indicated that O3 is likely titrated there. Additionally, the results indicate that non-point source emissions of NO2 are high enough to results in exceedances of the O3 standard limit. Overlay back trajectory maps showed that sites in the east are more frequently impacted by pollution transported from the Mpumalanga Highveld, Vaal Triangle and the Johannesburg-Pretoria megacity if compared to the west. Conversely, cleaner air masses impact the west more than sites in the east.Peer reviewe

Rapid changes in biomass burning aerosols by atmospheric oxidation

Peer reviewe

Root-zone soil moisture variability across African savannas : From pulsed rainfall to land‐cover switches

The main source of soil moisture variability in savanna ecosystems is pulsed rainfall. Rainfall pulsing impacts water-stress durations, soil moisture switching between wet-to-dry and dry-to-wet states, and soil moisture spectra as well as derived measures from it such as soil moisture memory. Rainfall pulsing is also responsible for rapid changes in grassland leaf area and concomitant changes in evapotranspirational (ET) losses, which then impact soil moisture variability. With the use of a hierarchy of models and soil moisture measurements, temporal variability in root-zone soil moisture and water-stress periods are analysed at four African sites ranging from grass to miombo savannas. The normalized difference vegetation index (NDVI) and potential ET (PET)-adjusted ET model predict memory timescale and dry persistence in agreement with measurements. The model comparisons demonstrate that dry persistence and mean annual dry periods must account for seasonal and interannual changes in maximum ET represented by NDVI and to a lesser extent PET. Interestingly, the precipitation intensity and soil moisture memory were linearly related across three savannas with ET/infiltration similar to 1.0. This relation and the variability of length and timing of dry periods are also discussed.Peer reviewe

The effect of rainfall amount and timing on annual transpiration in a grazed savanna grassland

The role of precipitation (P) variability with respect to evapotranspiration (ET) and its two components, transpiration (T) and evaporation (E), from savannas continues to draw significant research interest given its relevance to a number of ecohydrological applications. Our study reports on 6 years of measured ET and estimated T and E from a grazed savanna grassland at Welgegund, South Africa. Annual P varied significantly with respect to amount (508 to 672 mm yr(-1)), with dry years characterized by infrequent early-season rainfall. T was determined using annual water-use efficiency and gross primary production estimates derived from eddy-covariance measurements of latent heat flux and net ecosystem CO2 exchange rates. The computed annual T for the 4 wet years with frequent early wet-season rainfall was nearly constant, 326 +/- 19 mm yr(-1) (T/ET=0.51), but was lower and more variable between the 2 dry years (255 and 154 mm yr(-1), respectively). Annual T and T/ET were linearly related to the early wet-season storm frequency. The constancy of annual T during wet years is explained by the moderate water stress of C4 grasses as well as trees' ability to use water from deeper layers. During extreme drought, grasses respond to water availability with a dieback-regrowth pattern, reducing leaf area and transpiration and, thus, increasing the proportion of transpiration contributed by trees. The works suggest that the early-season P distribution explains the interannual variability in T, which should be considered when managing grazing and fodder production in these grasslands.Peer reviewe

Free tropospheric aerosols over South Africa

Raman lidar data of one year was been analyzed to obtain information relating aerosol layers in the free troposphere over South Africa, Elandsfontein. In total, 375 layers were observed above the boundary layer during the period 30th January 2010 – 31st January 2011. The seasonal behavior of aerosol layer geometrical characteristics as well as intensive and extensive optical properties were studied. In general, layers were observed at higher altitudes during spring (2520 ± 970 m) while the geometrical layer depth did not show any significant seasonal dependence. The variations of most of the intensive and extensive optical properties analyzed were high during all seasons. Layers were observed at mean altitude of 2100 m ± 1000 m with lidar ratio at 355 nm of 67 ± 25 and extinction-related Ångström exponent between 355 and 532 nm of 1.9 ± 0.8