Particulate Matter (PM2.5) Characterization, Air Quality Level and Origin of Air Masses in an Urban Background in Pretoria

Abstract

Several sources have been identified as contributing to the concentration of ambient fine particulate matter, which has been associated to a variety of health issues. The chemical characteristics and sources of trace elements in PM2.5, as well as the air quality index, were investigated in this study. 24-h fine aerosol particles were collected in an urban area in Pretoria, South Africa, from April 2017 -April 2018. Eighteen trace elements were determined using an XEPOS 5 energy-dispersive X-ray fluorescence (EDXRF) spectrometer, while black and organic carbon were estimated using an optical transmissometer from the samples collected. The HYPLIT model (version 4.9) was used to estimate air mass trajectories. Health risk was calculated by comparing it to the World Health Organization's air quality index (AQI). The overall mean PM2.5 concentration of the collected sample equals 21µg/m 3 . Majority of PM2.5 exceedances were reported during mid-autumn and winter seasons, as compared to daily WHO guidelines and South African standards. S had the highest concentrations, greater than 1µg/m 3 . Ni, Se, Br and Sb showed they were extremely enriched, (EF>10) and suggestive of anthropogenic or non crustal origin The 24-h PM, soot, BC and OC were significantly different by the geographical origin of air masses (p<0.05). The AQI showed that 70% of the samples showed levels above the AQI range of good and healthy air. The findings include details on the concentration, composition, and potential sources of fine PM2.5, which is essential for policy formulation and mitigation strategies in South Africa's fight against air pollution.

Inhalation health risk assessment of ambient PM2.5 and associated trace elements in Cape Town, South Africa

“…Si had the highest median concentration (380 ng/m 3 ), followed by Cl (290 ng/m 3 ) and Ti (33 ng/m 3 ). Similarly, Si levels in other areas in South Africa were higher than those of Cl and Ti, namely the administrative capital Pretoria (Adeyemi et al 2022;Howlett-Downing et al 2022), Thohoyandou in a rural area (Edlund et al 2021), and the heavily industrialized Vaal Triangle area (Muyemeki et al 2021).…”

“…Cl levels in Cape Town were higher than in Pretoria or the Vaal Triangle area (an industrial area located inland about 600 km from the Indian Ocean), or in Thohoyandou (a rural area located inland about 2000 km north from Cape Town) (Adeyemi et al 2022;Edlund et al 2021;Howlett-Downing et al 2022;Muyemeki et al 2021). The most likely sources of the Cl in the PM2.5 filter samples in Cape Town are the Atlantic Ocean (20 km west from the Kraaifontein study site) and the Indian Ocean (25 km south from the study site) (Williams et al 2021;Alfeus 2021).…”

“…Kruskal-Wallis tests determined whether the median exposure variables differed significantly between seasons and months. Seasons were: Autumn (March to May), winter (June to August), spring (September to November) and summer (December to February); as done in other local studies (Adeyemi et al 2022;Howlett-Downing et al 2022). Wilcoxon's rank-sum tests investigated whether median exposure variables differed significantly between weekdays and weekends.…”

“…Equation (1) measured the uncertainty of the EDXRF analysis method (Norris et al 2014;Reff et al 2007). Other local studies followed the same approach to exclude elements with low S/N ratios (Adeyemi et al 2022;Howlett-Downing et al 2022).…”

Source apportionment of fine atmospheric particles in Bloemfontein, South Africa, using positive matrix factorization

“…Statistical analyses were performed with STATA, version 15 (Adeyemi et al, 2022 ; STATA, 2023 ). As reported by Van der Westhuizen et al ( 2022 ), according to the Shapiro–Wilk’s test, PM 2.5 levels and its chemical component concentrations did not show normal Gaussian distributions; hence, non-parametric tests were applied.…”