The organic fraction of atmospheric aerosols is 20 to 90 % of which only a small percentage has been chemically characterised. Two-dimensional gas chromatography with a time-of-flight mass spectrometer (GCxGC-TOFMS) is a powerful instrument used to chemically characterise organic compounds. Size-resolved characterisation and semi-quantification of ambient organic aerosol compounds were performed with a GCxGC-TOFMS for the first time in South Africa. Twenty-four-hour samples were collected for 1 year for three different size ranges. A combined total of 1056 different organic compounds could be tentatively characterised. The largest number of organic compounds tentatively identified was PM 2.5-1 (particles in the size range 1-2.5 μm), while this size fraction also had the highest total number of normalised response factors (∑NRF). On average, 52, 26, 6, 13 and 3 % of species tentatively identified were oxygenated species, hydrocarbons, halogenated compounds, Ncontaining compounds and S-containing compounds, respectively. Oxygenated compounds were the most abundant species. Alkane and mono-aromatic species were the largest number of hydrocarbons tentatively identified with the highest ∑NRFs. The largest number of oxygenated species tentatively characterised were carboxylic acids and esters, while ether compounds had the highest ∑NRFs. Most of the halogenated compounds tentatively identified were chlorinated species with the highest ∑NRFs in two size fractions. Iodate species had a significantly higher ∑NRF in the PM 2.5-1 size fraction. The largest number of N-containing J Atmos Chem species tentatively characterised with the highest ∑NRFs were amines. A small number of Scontaining compounds with low ∑NRFs were tentatively identified. The major sources of organic compounds measured at Welgegund were considered to be biomass burning and air masses moving over the anthropogenically impacted source regions.

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Emerging organic contaminants in wastewater are usually analyzed by targeted approaches, and especially estrogens have been the focus of environmental research due to their high hormonal activity. The selection of specific target compounds means, however, that most of the sample components, including transformation products and potential new contaminants, are neglected. In this study, the fate of steroidal compounds in wastewater treatment processes was evaluated by a nontargeted approach based on comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry. The potential of the nontargeted approach to generate comprehensive information about sample constituents was demonstrated with use of statistical tools. Transformation pathways of the tentatively identified compounds with steroidal four-ring structure were proposed. The purification efficiency of the wastewater treatment plants was studied, and the distribution of the compounds of interest in the suspended solids, effluent water, and sludge was measured. The results showed that, owing to strong adsorption of hydrophobic compounds onto the solid matter, the steroids were mostly bound to the suspended solids of the effluent water and the sewage sludge at the end of the treatment process. The most abundant steroid class was androstanes in the aqueous phase and cholestanes in the solid phase. 17β-estradiol was the most abundant estrogen in the aqueous phase, but it was only detected in the influent samples indicating efficient removal during the treatment process. In the sludge samples, however, high concentrations of an oxidation product of 17β-estradiol, estrone, were measured.

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A recent paper reported GCxGC-TOFMS analysis used for the first time in southern Africa to tentatively characterise and semi-quantify ~1 000 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, ∑NRFs). However, the total number of polar organic compounds and ∑NRFs between late spring and early autumn seemed relatively lower compared to the period from mid-autumn to midwinter , while there was a period during late winter and early spring with significantly lower total number of polar organic compounds and ∑NRFs. Relatively lower total number of polar organic compounds and corresponding ∑NRFs were associated with fresher plumes from a source region relatively close to Welgegund. Meteorological parameters indicated that wet 2 removal during late spring to early autumn also contributed to lower total numbers of polar organics and associated ∑NRFs. Increased anticyclonic recirculation and more pronounced inversion layers contributed to higher total numbers of polar organic species and ∑NRFs from mid-autumn to midwinter, 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 ∑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.