Analytical Sciences

Reversible Control of the Equilibrium Size of a Single Aerosol Droplet by Change in Relative Humidity

Shoji ISHIZAKA,* Kunihiro YAMAUCHI,** and Noboru KITAMURA**

*Department of Chemistry, Graduate School of Science, Hiroshima University, Kagamiyama, Higashi-hiroshima 739-8526, Japan
**Department of Chemistry, Faculty of Science and Department of Chemical Sciences and Engineering, Graduate School of Chemical Sciences and Engineering, Hokkaido University, Sapporo 060-0810, Japan

Noncontact levitation of single micrometer-sized water droplets in air can be achieved by a laser trapping technique. The equilibrium size of a water droplet is quite sensitive to relative humidity in the surrounding gas phase. In order to investigate the physical and chemical properties of single water droplets in air as a function of the droplet size or solute concentration, laser trapping experiments were conducted under controlled humidity conditions. In this study, we developed a trapping chamber equipped with a relative humidity controller and demonstrated the reversible control of the equilibrium size of a single droplet levitated in air through a change in relative humidity. Furthermore, relative humidity was successfully evaluated by means of cavity enhanced Raman spectroscopy of a trapped water droplet.

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