Size and composition of particulate emissions from motor vehicles in the Kaisermühlen-Tunnel, Vienna

Size segregated emissions of particle-phase species from on-road motor vehicles were investigated in the Kaisermühlen 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 26±10 mg veh−1 km−1 in PM2.5, 62±18 mg veh−1 km−1 in PM10 and 129±45 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=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.