- A new vehicle-exhaust concept is described which leads to a reduced risk for the health and for the environment from particulate matter (PM). The geometry of the exhaust induces particle grouping and coagulation leading to a shift in particle size distribution, which increases the mass/number of the larger particles at the expense of the reduction in the amount of smaller ones. Such a shift in size distribution has implications with respect to particle capturing from diesel engines and other facilities, and with respect to lower residence time of particles which are emitted to the air. The theoretical basis and the supportive experiments are described. The results show that the concept is easy to apply and has significant implications with ramification to reduction of the concentration of submicron PM in main roads, and in work places.