A novel process using a cascade of packed columns to separate submicron particles from gases with high efficiency is presented. The process is based on the enlargement of the submicron particles by heterogeneous condensation. The particle enlargement as well as the collection of the droplets is achieved in the packed columns. Each column of the cascade is trickled with water which is alternately colder or warmer than the gas. The temperature difference between the gas and the water is required to achieve supersaturation of the vapour and correspondingly droplet growth by condensation in each column. The performance of the process is evaluated by experimental investigations. The collection efficiency of a two-stage cascade is determined using different submicron particles, such as residual particles, quartz particles, and paraffin oil droplets. It is shown that high collection efficiencies can be obtained by this separation process, also at high particle number concentrations. Since a new supersaturation is achieved in each column, large droplets are formed which are collected at the packing material of the columns with high efficiency. Correspondingly, submicron particles are separated with high performance by cascading packed columns.