The hydrolysis of a solid NaOH microparticle in humid nitrogen and the chemical reaction between the resulting NaOH solution microdroplet and SO2 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 SO2 gas. Raman spectra and elastic resonance spectra collected during the reactions indicate that low SO2 concentrations in the gas phase yield NaHSO3 while high SO2 concentrations result in NaSO3 as the product. These results indicate that the reversibility of the key reactions becomes important when the SO2 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)