Formation of condensation nuclei in city air, by ultraviolet radiation of wavelength greater than 2900A

Abstract

In the initial stages of condensation of water vapour in the atmosphere, an important part is played by minute particles contained in the air, which act as nuclei, or centres of condensation. John Aitken(1), a Scottish scientist, who lived from 1839 to 1919, carried out much of the pioneer research on these minute particles, now commonly called condensation nuclei. He showed that clouds of water droplets do not normally form in air unless condensation nuclei exist to act as centres of condensation. Condensation nuclei range in size from about 10 -3 cm. to 10 -7 cm., and they can remain suspended in the atmosphere for a long time since their velocities of fall are very small.