Charge induced stability of water droplets in subsaturated environment

J K Nielsen,D Rzesanke,C Maus,T Leisner

doi:10.5194/acp-11-2031-2011

Abstract

Abstract. Atmospheric liquid and solid water particles are stabilized if they are coated with either negative or positive electric charge. The surface charge causes an increase of the partial pressure of water vapour close to the surface of each particle, effectively allowing the particles to remain in their condensed phase even if the environmental relative humidity drops below unity. The theory, briefly presented in this paper, predicts a zero parameter relation between surface charge density and water vapour pressure. This relation was tested in a series of Electrodynamic Balance experiments. The measurements were performed by stabilizing charged droplets of pure water near an ice-surface. We observed a divergence in radius as the temperature approached the freezing point from below. We find that the measurements confirm the theory within the experimental uncertainty. In some cases this generally overlooked effect may have impact on cloud processes and on results produced by Electrodynamic Balance experiments.

Highlights

A few field measurements performed at different locations in the tropics has lead to observations of ice particles in the lowest stratosphere (Nielsen et al, 2007; Chaboureau et al, 2007; de Reus et al, 2008; Corti et al, 2008)
The surface charge causes an increase of the partial pressure of water vapour close to the surface of each particle, effectively allowing the particles to remain in their condensed phase even if the environmental relative humidity drops below unity
During the experiment the Electrodynamic Balance (EDB) chamber is kept in a subsaturated state, i.e. the water vapour partial pressure is kept below the saturation water vapour partial pressure over a plane liquid surface

Summary

Introduction

A few field measurements performed at different locations in the tropics has lead to observations of ice particles in the lowest stratosphere (Nielsen et al, 2007; Chaboureau et al, 2007; de Reus et al, 2008; Corti et al, 2008). Occurrence of ice particles in the stratosphere is somewhat unexpected since the stratosphere is generally subsaturated with respect to ice. Occurrence of ice particles in the stratosphere is somewhat unexpected since the stratosphere is generally subsaturated with respect to ice This is the case in the measurements of Khaykin et al (2009). These measurements must prompt speculations about which mechanisms could prevent ice from

Theory of charged hydrometeors

Non-equilibrium

Experimental setup

Perspectives

Conclusions