Abstract
We described efficient formation of water aerosol/droplet upon irradiating wet ambient air by a UV lamp (Hg lamp, 185nm) or UV laser (ArF laser, 193nm) in the laboratory. Particle formation was observed by light scattering and mass spectroscopy. With an observation of reaction-intermediates, namely ozone and HO_2 radical, and computer simulations of the gas phase reactions, we proposed the mechanism of photochemical hydrogen-peroxide formation, which serves as the nucleus for water condensation. It is shown that in the present systems a small supersaturation can make particle growth by thermodynamic considerations of the system.
