In the present work, size distributions and total concentrations of ultrafine particles generated during high velocity impacts of metals are shown. The measure of ballistic-generated particles was performed under controlled impact conditions: Taylor cylinder impact tests were designed and performed using a light gas-gun facility. Two materials were investigated, high purity copper 99.99% and aluminum 7075 T6, with cylinders of two different lengths impacting against a steel anvil. Tests were performed in impact chamber and recorded with a high frame rate camera. High-resolution time measurements of particle distributions and total concentrations were performed through fast mobility particle sizer and aerodynamic particle sizer spectrometers as well as condensation particle counters. Particle emission factors in terms of number and mass were also evaluated. The main result of the research was the measure of high particle generation in the ultrafine range: particle number distributions with a mode of 10 nm were detected; furthermore, number emission factors comparable to the ones typical of combustion phenomena were estimated. Finally, the number of particles emitted (larger than 10(12) part impact(-1) for both the materials) was found strictly related to the impact velocity and the contact surface area between projectile and anvil: these findings seem to indicate that the friction phenomena govern the particle formation process. (C) 2012 Elsevier Ltd. All rights reserved.