Abstract
Aerosol water droplets play important roles in the earth’s climate and in the atmospheric chemistry. Noncontact levitation of a single micrometer-sized water droplet in air can be achieved by a laser trapping technique and, therefore, the laser trapping technique is a powerful means to study the aerosol chemistry. In this paper, in situ characterization of the chemical composition and size of an aerosol water droplet is demonstrated by means of laser trapping and Raman spectroscopy. Furthermore, the laser trapping technique is applied to direct observation of freezing processes of single micrometer-sized water droplets in air. An artificial experimental model system corresponding to the initial steps of precipitation in clouds can be constructed by employing the laser trapping technique and an optical microscope.
