Diesel Filters make Pollution Worse Greg Archer, UK Director Transport and Environment
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armakers can no longer claim new diesels are clean. Recent research published by Transport and Environment has exposed that even the most modern diesel cars belch out huge numbers of hazardous fine particles. 1 For a decade new diesel cars and vans have been fitted with a diesel particle filter (DPF) to collect particles in the exhaust. The DPF was thought to have solved the diesel particle problem, but diesels produce so much soot the filters quickly clog and need regular cleaning typically every 300 miles. This regeneration of the filter, which typically lasts around 25 minutes, releases huge numbers of the smallest, most hazardous particles. T&E commissioned Ricardo Engineering to conduct the tests on the road and in the lab. We tested 2 cars a Vauxhall Astra and Nissan Qashqai but would have found very similar results on every diesel car, van and urban buses and delivery trucks too. The tests measured a massive spike in the particle numbers during the time the filter was cleaned. The levels were so high the vehicles breached the particle num10
ber limit – by 32 to 115% but in standard testing the car is not considered illegal because tests are invalidated and redone when a regeneration occurs. In effect between 60 and 99% of all the particles emitted from the vehicle occur during the regeneration and are ignored.
“All diesel cars
should be banned from low emission zones, as Bristol has done .� The legal limit for particle number is 6x10 11 . Most diesels in routine driving produce emissions substantially lower than this. The Nissan measured levels
above the legal limit during the regeneration on both occasions, 7.9 and 8.5 x10 11.. The Astra was much worse seeing 1.3x10 12 particles being released during the regeneration per km - around 5 times the legal limit. The research shows diesels are an even more important source of particulates than previously thought and demonstrate that it is nonsense to suggest new diesel cars are clean. All diesel cars should be banned from low emission zones - as Bristol has done. T&E also found that many of the particles released are too small to be measured during a standard road test. Only solid particles larger than 23nm in diameter are measured in the test, but T&E measured solid particles as small as 10nm and this increased the total number of particles by be-
