Examination of an Urban City Bus Operating Conditions and Emissions

City busses are main vehicles for public transport to meet travel demand of the society. They operate where urban population is very dense and release such emissions as particulate matters (PM), nitrogen oxides (NOx), carbon monoxides (CO), and hydrocarbons (HC) where the population lives (Soylu et al., 2009, Gumrukcuoglu et al., 2008, Soylu, 2007, WHO, 2003). Unfortunately, concentrations of the released emissions are generally high enough to damage human health and there is no enough time for the emissions to be diluted in the air to harmless concentrations before they are inhaled by human receptors. It is well known from the literature that exposure to even relatively low concentrations of vehicle emissions exacerbates or provokes many diseases (WHO, 2005a, WHO, 2005b). Adverse health effects of the emissions have been known for many decades and in order to prevent these effects many strict legislations, which reduces the limits more than 90% over four decades, for vehicle emissions have been issued. However, urban populations in many developed countries are still suffering from urban transport sourced emissions (Duclaux, 2002, Colvile et al.,2001, Frey et al., 2009, Erlandsson et al., 2008). One of the important reasons for this is that the engine certification test cycles don’t represent the real world in-use operation of the vehicles and, hence, quantity of vehicle emissions to be released in the urban streets has not been reduced in parallel with the stringent emission legislations (Cocker et al., 2004, Lents et al., 2007). City buses generally use diesel engines as power source and emit carbon dioxide (CO2), water vapor (H2O), and nitrogen (N2) to the ambient air as the main products of engine combustion. The quantity of CO2, which is the major greenhouse gas (GHG), is proportional to the fuel used in transport activities and it is inevitable combustion product, however, it is not necessary to emit CO, HC, NOx, and PM, which are generally called local pollutants since they are more harmful where they are emitted. The emissions of the local pollutants from city busses depend strongly on engine combustion technology, exhaust after-treatment devices, fuel quality, vehicle aging, and operating conditions (Cocker et al., 2004, Lents et al., 2007, Regulation, 2009). Especially the bus operating conditions may have significant effects on the emissions. Depending on city traffic and road conditions which involves many short trips with frequent accelerations, decelerations, low rush hour speeds and various road grades, the emissions may change with an order of magnitude (Cocker et al., 2004). Urban transport operating conditions and especially the city bus operating conditions are quite specific for a particular city and, hence, the well known certification test cycles cannot represent accurately these conditions all over the world. For this reason EURO VI regulation