Before the introduction of air qual

Before the introduction of air quality standards, exhaust emissions used to be a major source of PM, especially for diesel cars(Miguel et al., 1998). Since then, PM emission standards for vehicleexhausts have become increasingly strict and now all new dieselpassenger cars are fitted with a diesel particulate filter (DPF).Bergmann et al. (2009) found that DPFs are very effective atreducing PM emissions, lowering the emitted mass of PM by 99.3%.This has resulted in greatly reduced particle emissions from dieselsin the last ten years (Thorpe and Harrison, 2008; InternationalCouncil on Clean Transportation, 2015).