Measurement of black carbon concentration as an indicator of air quality benefits of traffic restriction policies within the ecopass zone in Milan, Italy Giovanni Invernizzi a, * , Ario Ruprecht a , Roberto Mazza b , Cinzia De Marco b , Gri  sa Mo  cnik c , Costantinos Sioutas d , Dane Westerdahl e a LARS, Environmental Research Laboratory SIMG-Italian College GPs, ISDE-International Doctors for the Environment, Milan, Italy b Istituto Nazionale dei Tumori, Milan, Italy c Aerosol d.o.o., Ljubljana, Slovenia d University of Southern California, Los Angeles, CA, USA e Cornell University, Ithaca, NY, USA article info Article history: Received 14 January 2011 Received in revised form 27 March 2011 Accepted 4 April 2011 Keywords: Air pollution Particulate matter Aerosols Traffic pollution Black carbon Spatial variability abstract Traffic restrictions are an unpopular tool to mitigate urban air pollution, and a measurable improvement in air quality is needed to demonstrate the effectiveness of this measure. Previous attempts failed to detect measurable reductions of PM mass pollution within the areas subject to traffic restriction. However black carbon, which is emitted primarily by traffic sources, could be a PM metric more suitable than PM mass to demonstrate pollutant reductions. In this study we report the results of a black carbon monitoring campaign carried out in Milan, Italy, with the aim to detect - and demonstrate more suitably than PM mass - differences in local urban air quality among three zones located very closely with different traffic intensity. The study was carried out in three different days by measuring simultaneously black carbon and PM mass concentrations with fixed monitoring stations located in three main radial roads connecting the outskirts to the city center, each with three segments: 1) an outer one, with no traffic restrictions 2) an intermediate one, subject to the congestion traffic charge called “Ecopass”, where a ticket is required to enter for cars equipped with engines prior to Euro 4 standard; 3) the pedestrian zone (no cars admitted) of Duomo Square in the city center, where each of the three main roads ends. The results demonstrated a sharply declining gradient in black carbon levels from the outer zone, without traffic restrictions, to the more central areas, for all of the three radial main roads. The differ- ences in mean black carbon levels in the same day in the different traffic scheme locations were highly significant for each comparison. In contrast to the Black carbon results, mean PM 10 , PM 2.5 , PM 1 concentrations did not show significant differences among the different traffic zones on the different campaign days. The ratio of black carbon to PM 10 decreased by 47% and 62% in the Ecopass zone and in the pedestrian zone, respectively, as compared to the no-restriction zone. To the best of our knowledge this is the first study showing that within-city proximal areas with different traffic intensity are asso- ciated with different black carbon levels. These data suggest that black carbon is a highly relevant metric of traffic pollution and should be taken into consideration in demonstrating the effectiveness of air quality mitigation measures. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Atmospheric pollution from suspended particulate matter (PM) represents a risk factor for respiratory and cardiovascular diseases and for cancer, mainly due to the presence of combustion products in the composition of the PM (Dockery et al., 1993; Künzli et al., 2000, 2010; Pope et al., 2002; Biggeri et al., 2004). Traffic emis- sions are of particular concern in very congested metropolitan cities, since they are associated with overall mortality increase (Hoek et al., 2002), lung cancer risk (Beelen et al., 2008), and worsening of respiratory health in children (Brauer et al., 2002; Van Roosbroeck et al., 2008; Migliore et al., 2009; Rosenlund et al., 2009). In the Milan district of northern Italy, it is estimated that emissions from vehicular traffic amount to about 55% of PM10 (INEMAR, 2010), a regulated pollutant with daily concentrations limit values of 50 mgm 3 (as daily average not to be exceeded for * Corresponding author. Tel.: þ39 347246 8282; fax: þ39 0343 34315. E-mail address: ginverni@clavis.it (G. Invernizzi). Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2011.04.008 Atmospheric Environment 45 (2011) 3522e3527