Also, during a transition period, before particle filters came generally in use, a few manufacturers burned the exhausts at high temperatures in order to reduce particle size and to pass tests. These nano particles become irreversibly embedded in lung and heart tissue and even pass the blood/brain barrier. Where I live, the percentage of diesel engines was pushed over 50% by a "green" engines campaign during these critical years. We're going to find out, what this may mean in terms of long term health implications.