Application of Fluorescence Spectroscopy To Study the State of Water in Aerosols

Abstract

The knowledge of the state of water molecules, particularly the amounts of solvated water and free water in aqueous droplets, is valuable in understanding the hydration properties of atmospheric aerosols. A novel technique combining the use of an electrodynamic balance and a fluorescence dye, 8-hydroxyl-1,3,6-pyrenetrisulfonate (pyranine), was used to study the state of the water molecules in single levitated aqueous droplets from subsaturation to supersaturation concentrations. The steady-state fluorescence spectra of sucrose, glucose, and NaCl solutions doped with 100 ppm pyranine were measured. The fluorescence emission of pyranine is sensitive to the proton-transfer capacity of its microenvironment. When excited by radiation at around 345 nm, pyranine fluoresces and the spectrum consists of two peaks, one at about 440 nm and the other at about 510 nm, which correspond to the presence of solvated and free water, respectively. The fluorescence peak intensity ratios of the 440-nm peak to the 510-nm peak ...