An experimental study is presented, which assesses the capability of a novel concept of particle-grouping technique in reducing the emission of nano-particles from transportation systems. This size-class of emitted particles is known to be both more harmful for the health than the larger particles and far more difficult to manipulate, yet, as described here, the grouping concept leads to their elimination to some extent, by promoting their coagulation with particles in their vicinity. This is achieved with a "grouping exhaust" system that is designed to form a specific oscillating flow according to a mathematical model for each engine, based on engine characteristics [FUEL, 2010, 89: 2411-2416]. The system has shown previously to be efficient with respect to micron-sized particles while here the focus is on the nano-particles, showing its efficiency in reducing the number of those particles for both diesel as well as gasoline engines and at a wide range of operating conditions. (C) 2015 Elsevier Ltd. All rights reserved.