A Formation of Atmospheric Aerosol Particles Due to Gas-to-Particle Conversion in Dark Conditions and the Particles’ Evolution in Large (3200 m3) Isolated Volume

absence. The study was carried out in the Large Aerosol Chamber (LAC) of Research and Production Association (RPA) "Typhoon" having 3200 m3 volume. Because of the large size of the LAC, it is possible to exclude the boundary conditions influence by chamber walls and the equipment inside the LAC on the processes under study. The LAC has two (external and internal) High Efficiency Particulate Air (HEPA) 13 class filters installed at the entrance and inside it. First, we fill out the LAC of the atmospheric air and close it. After that, we purify the air inside the LAC by the internal filter. The number concentration of particle sizes above 15 nm decreases down to 50 particles per cm3. However, after a while, we observe increasing the particle number concentration by more than two orders of magnitude. We suppose that new formed particles due to gas-to-particle conversion were detected. We again purify the air inside the LAC by the internal filter. The particle number concentration decreased down to 10-20 particles per cm3 and remained at this low value for more than 300 hours. Our experiments indicate the necessity to use the two-stage procedure for cleaning working areas, with a time gap enabling gaseous precursors to form new particles, removable by HEPA 13 filter. Regularities of the growth of the newly formed particles from 15 nm size to cloud condensation nuclei characteristic size under controlled conditions were investigated. The observed regularities could contribute to understanding the atmospheric aerosol formation process responsible for cloudiness and precipitations.