1. Department of Chemistry, University of the Free State, Bloemfontein, South Africa
2. School of Health Systems and Public Health, Faculty of Health Sciences, University of Pretoria, Pretoria, South Africa
3. Department of Occupational and Environmental Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Göteborg, Sweden
4. Department of Chemistry and Molecular Biology, Atmospheric Science Division, University of Gothenburg, Göteborg, Sweden