Atmospheric Environment 42 (2008) 2173–2186 Size and composition of particulate emissions from motor vehicles in the Kaisermu¨hlen-Tunnel, Vienna Markus Handler, Christoph Puls, Johannes Zbiral, Iain Marr, Hans Puxbaum, Andreas Limbeck à Institute of Chemical Technologies and Analytics, Vienna University of Technology, Getreidemarkt 9/164, Vienna A-1060, Austria Received 18 May 2007; received in revised form 4 October 2007; accepted 27 November 2007 Abstract Size segregated emissions of particle-phase species from on-road motor vehicles were investigated in the Kaisermu¨hlen Tunnel (Vienna, Austria) during April and May 2005. Emission factors were calculated from concentration differences between tunnel inside and tunnel outside samples, the distance between tunnel entrance and sampling location, the ventilation rate and the number of vehicles passing the tunnel. For a mixed car fleet with an average contribution of 9.6% heavy duty vehicles (HDVs) mean particle mass emissions of 26710 mg veh 1 km 1 in PM2.5, 62718 mg veh 1 km 1 in PM10 and 129745 mg veh 1 km 1 for total suspended particulates (TSPs) were observed. The released particles mainly consisted of elemental carbon (EC), organic carbon (OC) and the mineral components (MC ¼ Si, Fe, Ca, Al, Mg). They accounted for 34.4% (EC), 30.3% (OC) and 18.2% (MC) of total PM10 emissions and 68.5%, 8.7% and 14.9% of PM2.5 emissions, respectively. Trace metal emissions (As, Ba, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sb, Sn, Sr, Ti, V, Zn) contributed for less than 1% of total emissions in all size fractions. Emissions of coarse particles were found to be dominated by resuspended matter as well as by brake wear, whereas fine particles were mainly derived from combustion processes. On weekends for some components distinctly reduced emissions were observed which could be explained with changes in the driving conditions and/or fleet composition. r 2007 Elsevier Ltd. All rights reserved. Keywords: Particulate motor vehicle emissions; Size segregated emission rates; Trace metals; Tunnel study; HDV; LDV 1. Introduction Vehicle emissions make substantial contributions, both directly and indirectly, to atmospheric particle concentrations. Direct particulate emission sources from vehicles include their exhaust (Mulawa et al., 1997; Sagebiel et al., 1997), the mechanical wear of tires and brakes (Rogge et al., 1993; Garg et al., 2000), and the ejection of particles from the pavement (Kupiainen et al., 2005) and unpaved road shoulders (Moosmu¨ller et al., 1998) by re- suspension processes (Nicholson et al., 1989; Stern- beck et al., 2002). Indirect contributions include the emission of reactive gases, both organic and inorganic, which form secondary particulate matter via atmospheric transformations. Motor vehicle emission inventories normally used in air quality models are derived from tailpipe ARTICLE IN PRESS www.elsevier.com/locate/atmosenv 1352-2310/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2007.11.054 à Corresponding author. Tel.: +43 1 58801 15180; fax: +43 1 58801 15199. E-mail address: A.Limbeck@tuwien.ac.at (A. Limbeck).