Exhaust emissions of 23 individual city buses at Euro III, Euro IV and EEV (Enhanced Environmentally Friendly Vehicle) emission levels were measured by the chasing method under real-world conditions at a depot area and on the normal route of bus line 24 in Helsinki. The buses represented different technologies from the viewpoint of engines, exhaust after-treatment systems (ATS) and fuels. Some of the EEV buses were fueled by diesel, diesel-electric, ethanol (RED95) and compressed natural gas (CNG). At the depot area the emission factors were in the range of 0.3-21 × 10(14) # (kg fuel)(-1), 6-40 g (kg fuel)(-1), 0.004-0.88 g (kg fuel)(-1), 0.004-0.56 g (kg fuel)(-1), 0.01-1.2 g (kg fuel)(-1), for particle number (EFN), nitrogen oxides (EFNOx), black carbon (EFBC), organics (EFOrg), and particle mass (EFPM1), respectively. The highest particulate emissions were observed from the Euro III and Euro IV buses and the lowest from the ethanol and CNG-fueled buses, which emitted BC only during acceleration. The organics emitted from the CNG-fueled buses were clearly less oxidized compared to the other bus types. The bus line experiments showed that lowest emissions were obtained from the ethanol-fueled buses whereas large variation existed between individual buses of the same type indicating that the operating conditions by drivers had large effect on the emissions.

Aerosol Physics Laboratory Department of Physics Tampere University of Technology P O Box 692 33101 Tampere Finland

Atmospheric Composition Research Finnish Meteorological Institute P O Box 503 FI 00101 Helsinki Finland

Department of Environmental Sciences University of Helsinki P O Box 65 FI 00014 Helsinki Finland

Department of Physics University of Helsinki P O Box 64 00014 Helsinki Finland

Department of Technology Metropolia University of Applied Sciences P O Box 4021 00180 Helsinki Finland

Helsinki Region Environmental Services Authority HSY P O Box 100 00066 HSY Helsinki Finland

KVM Katedra vozidel a motorů Fakulta strojní Technická univerzita v Liberci 461 17 Liberec 1 Czech Republic

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