On-board Emission and Odour Measurements on Euro 2 Buses Retrofitted with Different Combinations of PM Traps and SCR

The Flemish Transport Company equipped two Euro 2 buses with two different ‘Combined Solution’ systems for the simultaneous reduction of NO_x and PM. Pre versus post ‘Trap+SCR’ emissions of CO, THC, NO_x and PM together with post emissions of NH₃ were measured over a bus line in Ghent and over driving cycles on a proving ground. NO_x was reduced from 70 to 88%. The PM emission reduction however was over 90% for the system with closed trap and only 20% at best for the open trap one. Overall NH₃ emissions were low in real traffic and over most test cycles i.e. below 12 ppm. Pre versus post ‘Trap+SCR’ odour concentration measurements by dynamic olfactometry on one bus showed odour removal efficiencies of 71% and 79% on respectively idle and DUBDC cycle. The tail pipe odour concentration in European odour units was respectively 2818 and 1177 ou_E/m³.