Mechanisms of nucleus-forming reactions in the atmosphere

Measurements of Aitken nucleus concentrations in the free air at sea level showed that solar radiations are likely to have a striking effect on the rate of nucleus formation. A series of controlled experiments were performed in order to understand the mechanisms involved. The experiments suggest that a variety of interesting reactions are likely to occur in the atmosphere, leading to the formation of Aitken nuclei. The primary reactants in these processes are some of the trace gases of the air, water vapor, solar radiation, and ionizing radiation, all of which have a complex role. A comparative study of the daytime variations in the nucleus concentration in the free air and nucleus formation in filtered air showed similar trends. The possible effects of solar and ionizing radiations were studied by artificial irradiation of highly filtered air and different gas mixtures in a laboratory system. The mechanisms of production of nuclei by sulfur dioxide, chlorine, and oxides of nitrogen have been investigated in these experiments. The following effects of ionizing radiation and solar radiation inferred from these studies are discussed: (1) the radiolytic reactions in the atmosphere caused by natural ionizing radiations give rise to products, possibly ions and free radicals, that aid the formation of nuclei; and (2) certain chemical species formed by the effects of solar radiation on the air are likely to aid the formation of nuclei even in the absence of sunlight. The relevant chemical reactions, based on the laboratory studies, have been proposed. Stable sizes of acid nuclei have been calculated on the basis of Raoult's law and the Kelvin equation.