Retrospective on the Introduction of Particle Filters to Eliminate Emissions of Nanoparticles from Engine Exhaust Gas

The particle filter for most diesels and some petrol categories is now state of the art. The worldwide population is estimated to be >250 million vehicles with filters. The nanoparticle concentration in ambient air is thus reduced in Switzerland to one third of the status of 2005 and worldwide premature deaths by traffic related ambient air is reduced by >2 million cases annually. This success story started in 1995 when SUVA, the Swiss occupation health authority, had to guarantee safety and health in the world's largest railway transalpine tunnelling system, NEAT, scheduled to be built from the year 2000. The solution was VERT certified diesel particle filters (DPFs) on all engines without any exceptions. Transfer to other applications and other countries, however, had to overcome serious resistance of industry and politics which delayed the process remarkably until filters became mandatory by the EU-legislation 2011. The decisive element was the introduction of the particle number (PN) limit for solid particles of sizes 10-500 nm in place of particulate matter (PM) mass in 1995. Many vehicles are still waiting for filters worldwide and the effect of this highly effective and cost-efficient tool on health and global warming could be more than tripled.