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1 Switzerland is enforcing the use of particulate traps for offroad applications like construction as well as for occupational health applications like tunneling. This decision is based on the results of the VERT-project (1994-1999), which included basic aerosol research, bench screening and field testing of promising solutions as well as the development of implementation tools like trap specification, certification scheems and field control measures. On the other hand there is no corresponding regulation for city-buses yet although PM 10 is about 2× above limit in most Swiss cities. Public pressure however is growing and city transport authorities have reacted by retrofitting Diesel city-buses instead of waiting for cleaner engine technology or CNG-conversions. The favored trap system with about 200 retrofits so far is the CRT.

Microfibers with high specific micro-surface can be knitted into two-dimensional structures with large internal porosity. Catalytically active metals can be deposited on the fibers with high dispersion by wet-impregnation, sol-gel or CVD, respectively. These microfiber knits may be used for exhaust gas treatment systems with a triple function: particle filtration, gas conversion and muffling. The total oxidation of propane on Pd and Pt coated fibers has been studied as a test reaction. Conversion temperature could be remarkably reduced compared to cellular structures. For a bimetallic (Pt-Pd) coating, the activity is independent of humidity or oxygen concentration. Thus a catalytic converter based on micro-fiber knits appears feasible. Its high mass and heat transfer prevent hot spots. And it functions as submicron filter for combustion aerosols. Integrated electric heating can also be provided in case of low gas temperatures. First tests on engines show promising results.