The purification system has both a passive and an active regeneration phase, according to the article. The passive regeneration happens during open road driving, when the exhaust temperature ranges from 350 to 500 degrees Celsius and involves the diesel soot stored in the catalytic converter being converted into CO2. The active regeneration takes place mostly during city driving. Every 250-300 miles, internal processes within the engine increase the exhaust temperature to around 600 degrees Celsius, which converts the stored diesel soot into CO2. The system has been used Volkswagen vans in Germany since 2005.