Density enhancement of nano-sized and submicron-sized water droplets induced by charges released from corona discharge

Corona discharge is widely used as an ionization source in field experiments of weather modification induced by charged particles due to its high efficiency and economy. However, deficient research efforts have been devoted to the effects of corona discharge on the size distribution and evolution of droplets in the humid air. In this paper, the characteristic of water droplets spectrum evolution in humid air with unipolar corona discharge is studied by an electrical low pressure impactor (ELPI) experiment in a 96 m³ cloud chamber. Results show that nano-sized water droplets with diameters from 9 nm to 25 nm grow rapidly because of the inducement of charges released from corona discharge. Additionally, an increase in the concentration of submicron droplets appears at 20 min. To reveal the potential mechanism of the phenomena, the average charge values of charged droplets measured by ELPI are further analyzed. Meanwhile, the relationship between saturated vapor pressure over charged droplet's surface and its radius is discussed by the modified Kelvin–Thomson equation. Results show that, for the density enhancement of nano-sized droplets, condensational growth induced by charges released from corona discharge dominates significantly. The subsequent increase in the density of submicron-sized droplets is regarded as the break-up of the micron-sized droplets, with the process of evaporation when droplets are approaching the Rayleigh limit in the sub-saturated environment. This research may bring some new perspectives to further study of weather modification and cloud-seeding induced by charged particles, such as by increasing condensed nuclei density, broadening cloud droplets spectrum, and suppressing the evaporation of cloud droplets, etc. (paper)