Observation of Unusual High Particulate Mass and Number Concentration during Traffic Ban Hours of the 2009 Car Free Sunday in the Brussels Urban Area

Abstract: Every year, since 2002, the Brussels authorities organize a car free day on the third Sunday of September. This very interesting experience has revealed some valuable information concerning traffic-related gaseous pollutants and particulates. On the car free Sunday of 2006 very high PM10 and PM2.5 mass concentrations were measured, along with very low concentrations for nitrogen oxides, carbon monoxide and dioxide. The car free Sunday of 2009 also showed very interesting results. During the traffic ban hours, particulate mass concentration and particulate number concentration peaked to one of the highest values for the whole year 2009. Black Carbon however was the only measured particulate component whose concentration continued to decrease during the traffic ban period.