Atmospheric chemistry of CH₃CHO: the hydrolysis of CH₃CHO catalyzed by H₂SO₄

Abstract

Elucidating atmospheric oxidation mechanisms and the reaction kinetics of atmospheric compounds is of great importance and necessary for atmospheric modeling and the understanding of the formation of atmospheric organic aerosols. While the hydrolysis of aldehydes has been detected in the presence of sulfuric acid, the reaction mechanism and kinetics remain unclear. Herein, we use electronic structure methods with CCSD(T)/CBS accuracy and canonical variational transition state theory combined with small-curvature tunneling to study the reaction mechanism and kinetics of the hydrolysis of CH₃CHO. The calculated results show that the hydrolysis of CH₃CHO needs to overcome an energy barrier of 37.21 kcal mol^-1, while the energy barrier is decreased to -9.79 kcal mol^-1 with a sulfuric acid catalyst. In addition, the calculated kinetic results show that the H₂SO₄H₂O + CH₃CHO reaction is faster than H₂SO₄ + CH₃CHOH₂O. Additionally, the H₂SO₄H₂O + CH₃CHO reaction can play an important role in the sink of CH₃CHO below 260 K occurring during the night period when OH, H₂SO₄, and H₂O concentrations are 10⁴, 10⁸, and 10¹⁷ molecules cm^-3, respectively, because it can compete well with the CH₃CHO + OH reaction. There are wide implications in atmospheric chemistry from these findings because of the potential importance of the catalytic effect of H₂SO₄ on the hydrolysis of CH₃CHO in the atmosphere and in the formation of secondary organic aerosols.