Air pollution is the single greatest environmental health risk worldwide. Reducing risks to human health from degraded air quality, then, is central for improving people’s lives and well-being. Fine particulate matter (PM2.5), in particular, is the most serious pollutant globally from a human health perspective. Chronic exposure even to moderate levels of PM2.5 substantially increases the risk of heart disease and stroke, the leading causes of death in OECD countries. It also increases the risk of respiratory diseases, including lung cancer, chronic obstructive pulmonary disease and respiratory infections (WHO, 2016; Burnett et al., 2014; Brauer et al., 2016). Other pollutants of most concern are small particulates (PM10), ozone (O3), nitrogen dioxide (NO2) and sulphur dioxide (SO2). Emissions from transport, industry, electricity generation, agriculture and domestic (household) sources are the main contributors to outdoor air pollution (EEA, 2016a; Caiazzo et al., 2013).