The present invention discloses a method for catching particles having diameters size down to the nanometer level including a first step of increasing particle diameters of particles contained in an outlet gas from a fabrication process of nano-particles or an exhaust from a combustion; and a second step of introducing the resulting effluent from the first step into a rotating packed bed. The first step involves contacting the gas/exhaust with droplets or water vapor, creating collision of the nano-particles with the droplets or condensation of water vapor using the nano-particles as condensation nuclei, so that the size of the nano-particles increases to the micro level. The second step uses the minute water drops generated from and the hindrance of the rotating packed bed to catch the micro-particles in the gas/exhaust under a relatively high centrifugal force. The first step can occur in the rotating packed bed if the gas/exhaust is introduced directly into the rotating packed bed and has a sufficient long residence time in the rotating packed bed.