Ultraviolet irradiation of aqueous nitrite (NO2 –) quickly generates hydroxyl (OH) and nitric oxide (NO) radicals, which are subsequently consumed concomitantly with the generation of N x O y species. Recently, dissolved formaldehyde (CH2O) in aqueous solution (e.g., methanediol, CH2(OH)2), has been regarded as the precursor in the formation of atmospheric formic acid (HCOOH) via the reaction with OH and cascading processes (Nature2021593233237). In this work, a step-scan Fourier transform interferometer was utilized to monitor the time-resolved difference infrared spectra of NaNO2 aqueous solution in the presences of methanediol and methanol upon pulsed irradiation at 355 nm. The fates of the dinitrogen trioxide (N2O3), generated via a series of reactions of OH, NO, and NO2 –, differed in the presences of CH2(OH)2 and CH3OH. The decay of N2O3 via hydrolysis with H2O was retarded more by CH3OH than by CH2(OH)2. The monohydroxyl group of CH3OH does not behave like the hydroxyl group of water, whereas the two hydroxyl groups of CH2(OH)2 can be treated as a water reservoir via the quick equilibrium between H2O and CH2O, further facilitating the hydrolytic solvation reaction of N2O3. The observed difference in reaction kinetics involving hydration should be thoroughly taken into consideration in formaldehyde-related aqueous reactions.

Nitrite (NO2−) is one of the common salts in the aqueous aerosol, and its photolytic products, nitric oxide (NO) and hydroxyl radical (OH), have potential for use in the oxidation...