Political institutions generally desire to use the best available scientific evidence when formulating policy. In South Africa, the declaration of the Priority Areas where 'ambient air quality standards are being, or may be, exceeded' (according to the National Environmental Management: Air Quality Act, 2004) is an example of a policy initiative that was prompted by quantitative evidence-measurements of ambient air pollution levels. National Priority Areas have been declared in the Vaal Triangle in 2006, in the Highveld in 2007 and in the Waterberg-Bojanala region in 2012. The Department of Environment, Forestry and Fisheries (DEFF, formerly the Department of Environmental Affairs) established a network of 6 ambient air quality monitoring stations in the Vaal Triangle and 5 monitoring stations in the Highveld Priority Area to inform the emission reduction strategies and track progress in reducing ambient pollution levels. The summarised data from these monitoring stations is presented annually by the National Air Quality Officer in the State of the Air Report. In this issue of the Clean Air Journal, there are two papers (Feig et al., 2019 and Govender and Sivakumar, 2019) that have subjected the 10+ years of data from these monitoring stations to more rigorous trend analysis, which allows reflection on progress made to date and future regulatory priorities.