The Environmental Control of Individual Aqueous Particles in a Cubic Electrodynamic Levitation System

The experimental investigation of aerosol particles often requires special apparatus to ensure that the walls of the system interfere minimally with the measurements. Electrodynamic levitation offers an attractive approach because the particle, when suitably charged, is held away from the system walls by time-dependent electric fields. A new electrodynamic levitation system has been developed expressly for investigating aqueous particles in controlled gaseous environments. A cubic cell was used in conjunction with the carefully controlled introduction of gas into the cell to form a wall-less flow reactor that is ideal for thermodynamic and kinetic studies involving reactive reagents. Unlike most previous cell configurations, the cubic geometry permits three-axis position control of the particle and an ability to measure the gravitational and drag forces simultaneously and independently when the gas flow is horizontally aligned. Preliminary results at room temperature of the mass gained by salt and sulfuric acid particles exposed to various humidities show the basic characteristics of the cell. New results with sulfuric acid particles exposed simultaneously to the vapors of water and nitric acid show that nonvolatile and volatile solutes cause aqueous particles to behave in qualitatively different ways. Such results confirm that cloud formation in the atmosphere should be enhanced by the presence of soluble trace gases under suitably low-temperature conditions.