In the paper the activities on reduction of Particle Mater emission of city busses in public transportation in City of Biel (Switzerland) were discussed. Following objectives were pursued in the 4 years project: clearing up of the usefulness of water-emulsion fuel, of exhaust gas emissions of busses before and after DPF retrofit, of efficiency of filter additivesupported regeneration, testing of coated CRT and preliminary tests with different lube oils. As most important statements it can be pointed out that: water-fuel emulsion combined with CRT reduces significantly all emission components and supports the DPF regeneration but the influences of oil quality on the particle emissions need further investigations. It was also find out, that CRT doesn’t work satisfactorily in the Euro 1 busses, while in Euro 2 and Euro 3 busses its cleaning periods were longer than 150 000 km.