Experiments in different climatic regions of Russia have shown that bipolarly ionizing radiation with intensity from 5 to 1012 ion pairs/(cm3 · s) independently of its type can stimulate formation of new aerosol particles of 5-100 nm in diameter at energy consumption about 100 eV per 10 molecules of the condensate. These particles have basic properties of cloud condensation nuclei and can participate in modification of cloud processes. Main factors reducing the efficiency of the gas-particle conversion are the relative humidity and air temperature, as well as the content of some gases. The intense and long-term ionization minimizes the effect of these factors. The main factor controlling the new aerosol generation, all other factors the same, is the absorbed energy of ionizing radiation R, which threshold value sufficient for generating new particles under natural ionization in the near-surface atmosphere is 103 eV/cm3.