New insights into 3M3M1B: the role of water in ˙OH-initiated degradation and aerosol formation in the presence of NOX (X = 1, 2) and an alkali

Abstract

The oxidation mechanisms and dynamics of 3-methoxy-3-methyl-1-butanol (3M3M1B) initiated by ˙OH radicals were assessed by the density functional theory and canonical variational transition state theory. The effects of ubiquitous water on the title reactions were analyzed by utilizing an implicit solvation model in the present system. The results suggested that aqueous water played a negative role in the ˙OH-initiated degradation of 3M3M1B with an increase in the Gibbs free barriers. Meanwhile, the barriers were almost independent when explicit water molecules were involved in the gaseous phase, which could reduce the rate constant by approximately 3 orders of magnitude. The kinetic calculations showed that the rate constants were smaller by about 15, 9, 8, and 8 orders of magnitude for hydroxyl-, ammonia-, formic acid-, and sulfur acid-participating reactions, respectively, than that from an unassisted reaction. The results indicated that water, hydroxyl, ammonia, formic acid, or sulfur acid could not facilitate the title reaction when performed in the atmosphere. The investigations of the subsequent oxidation processes of the alkyl radical CH₃OC(CH₃)₂CH₂C·HOH indicated that CH₃OC(CH₃)₂CH₂CHO was the most favorable product by eliminating an HO₂˙ radical. Additionally, the HO₂˙ radical could serve as a self-catalyst to affect the above reaction through a double proton transfer process. With the introduction of NO, CH₃OC(CH₃)₂CH₂COOH and HNO₂ were found to be the main products, which may be regarded as the new source of atmospheric nitrous acid. In the NO₂-rich environment, the peroxynitrate of CH₃OC(CH₃)₂CH₂CH(OONO₂)OH could be formed via the reaction of the CH₃OC(CH₃)₂CH₂CH(OO˙)OH radical with NO₂. The degradation mechanism of CH₃OC(CH₃)₂CH₂CH(OONO₂)OH in the presence of water, ammonia, and methylamine was demonstrated, and it was shown that water, ammonia, and methylamine could promote the formation of nitric hydrate and nitrate aerosol. The main species detected in the experiment were confirmed by a theoretical study. The atmospheric lifetimes of 3M3M1B in the temperature range of 217–298 K and altitude of 0–12 km were within the range of 6.83–8.64 h. This study provides insights into the transformation of 3M3M1B in a complex environment.