Experiments on the formation of particles by chemical reactions in the dark and under influence of light

Abstract

Some experiments concerning the photochemical production of condensation nuclei are described. Preliminary measurements of filtered atomospheric air, initially free of particles yielded high concentrations of particles by reactions in the dark when the air was previously irradiated by sunlight. In further investigations a definite composition of pure gases was used. The formation of nitric acid particles from NO2 in pure nitrogen of different relative humidities in the dark and under influence of light was investigated. No particle formation was found which could be correlated to any production of nitric acid nuclei. Even within a spectral region in which photolysis of NO2 takes place no HNO3-nucleation could be found. The particles detected under certain conditions of irradiation originate from impurities in the walls of the reaction chamber. Particle growth in an irradiated mixture of N2 and NO2 with benzene is demonstrated and the mean radius of particles is calculated from measurement with a diffusion battery.