White light Mie resonance spectroscopy used to measure very low vapor pressures of substances in aqueous solution aerosol particles.

We report a novel and fairly simple optical technique for sizing and measuring the evaporation rates of aqueous solution aerosol particles. A ball-lens LED with high degree of spatial coherence is used as a "white" light source to excite the Morphology Dependent Resonance (MDR) spectra of a microdroplet levitated in an electrodynamic balance (EDB). The spectra are recorded by an Optical Multichannel Analyzer. We show that very low vapor pressures of substances in aqueous solution particles can be measured for different temperatures and relative humidities (hence for different concentrations). As an application we measured the vapor pressure and the enthalpy of vaporization of aqueous malonic acid, a substance of interest for atmospheric science.