The EU directive on air quality (Directive 2008/50/EC) sets limit values for particulate matter in Europe, i.e., 40 µg m -3 for PM 10 and 25 µg m -3 for PM 2.5 , while there are also limits for daily values, e.g., 50 µg m -3 for PM 10 . Currently, the effect 20 induced by the adoption of restricted traffic areas on PM is a debated topic due to the difficulties in disentangling the effect from of other effects such as seasonality and the influence of weather conditions . Meteorological conditions can hence influence the exacerbation, dispersion, and reactivity of PM in urban areas .