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1 The VERT project aimed at curtailing the construction site diesel emissions of ultra-fine particles to 1% of the raw emissions. Thus, compliance with occupational health legislation should be achieved. Particulate traps have attained this target. In contrast, engine tuning, reformulated fuels and oxidation catalytic converters are almost ineffective. This paper reports on the concluding project stage in which 10 traps were field tested during 2 years. Subsequent detailed measurements confirmed the excellent results: > 99% filtration rate was achieved in the nano-particulate range. The PAH, too, were very efficiently eliminated. Trap deployment becomes therefore imperative to fulfill VERT-targets.

Increasing concern, about the health risk due to solid aerosols from engine combustion, has provoked more stringent imission limits, for soot particles in the range of pulmonary intrusion, at critical work-places (e.g. tunnel sites, see Table 1). Within the scope of the joint European project VERT, these emissions were characterized and their effective curtailment through exhaust gas after-treatment investigated. Diesel engines, irrespective of design and operating point, emit solid particulates in the range of 100 nm, at concentrations above 10 million particulates per cm3. Engine tests showed that a drastic curtailment of pulmonary intruding particulates seems not feasible by further development of the engine combustion, nor by reformulation of fuels, nor by deployment of oxidation catalytic converters. Particulate traps, however, can curtail the total solid particulate count, in the fine particulate range 15-500 nm, by more than two orders of magnitude.

Diesel engines are irreplaceable in tunnel construction. The particulate emissions of present day engines are so high that the imission limits valid since 1991 cannot be attained by ventilation alone. This problem had to be solved preparatory to the large tunnel projects in Switzerland, Austria and Germany. Several retro-fitting measures were investigated both in the laboratory and in field tests, within the scope of the Project VERT. Oxidation catalytic converters, exhaust gas recirculation, and the usage of special fuels cannot be recommended. Particulate trap deployment, in different systems, was mostly successful. Particular attention was focused on the dependable filtration of finest particulates < 200 nm. The VERT proved that exhaust gas after-treatment with particulate traps is feasible, cost effective and controllable in the field. Pertinent directives are in discussion.