The hydrolysis of a solid NaOH microparticle in humid nitrogen and the chemical reaction between the resulting NaOH solution microdroplet and SO<sub>2</sub> gas have been studied with the use of elastic and inelastic (Raman) light scattering. A single solid NaOH particle was levitated electrodynamically in a reaction chamber and exposed to water vapor. After hydrolysis/deliquescence, the resulting solution droplet was exposed to SO<sub>2</sub> gas. Raman spectra and elastic resonance spectra collected during the reactions indicate that low SO<sub>2</sub> concentrations in the gas phase yield NaHSO<sub>3</sub> while high SO<sub>2</sub> concentrations result in NaSO<sub>3</sub> as the product. These results indicate that the reversibility of the key reactions becomes important when the SO<sub>2</sub> concentration is low.
Christopher L. Aardahl and E. James Davis, "Gas/Aerosol Chemical Reactions in the NaOH-SO2-H2O System," Appl. Spectrosc. 50, 71-77 (1996)