Comparing the Reactivities of Methanol and Methanediol in the Photolysis of Aqueous Nitrite Solution.

Ultraviolet irradiation of aqueous nitrite (NO 2 - ) 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 (CH 2 O) in aqueous solution (e.g., methanediol, CH 2 (OH) 2 ), has been regarded as the precursor in the formation of atmospheric formic acid (HCOOH) via the reaction with OH and cascading processes ( Nature 2021, 593, 233-237). In this work, a step-scan Fourier transform interferometer was utilized to monitor the time-resolved difference infrared spectra of NaNO 2 aqueous solution in the presences of methanediol and methanol upon pulsed irradiation at 355 nm. The fates of the dinitrogen trioxide (N 2 O 3 ), generated via a series of reactions of OH, NO, and NO 2 - , differed in the presences of CH 2 (OH) 2 and CH 3 OH. The decay of N 2 O 3 via hydrolysis with H 2 O was retarded more by CH 3 OH than by CH 2 (OH) 2 . The monohydroxyl group of CH 3 OH does not behave like the hydroxyl group of water, whereas the two hydroxyl groups of CH 2 (OH) 2 can be treated as a water reservoir via the quick equilibrium between H 2 O and CH 2 O, further facilitating the hydrolytic solvation reaction of N 2 O 3 . The observed difference in reaction kinetics involving hydration should be thoroughly taken into consideration in formaldehyde-related aqueous reactions.