Reaction between Criegee intermediates and hydroxyacetonitrile: reaction mechanisms, kinetics, and atmospheric implications

Abstract

Hydroxyacetonitrile (HOCH2CN) is released from wildfires and bleach cleaning environments, which is harmful to the environment and human health. However, its atmospheric lifetime remains unclear. Here, we theoretically investigate the reactions of Criegee intermediates (CH2OO and syn-CH3CHOO) with HOCH2CN to explore their reaction mechanisms and obtain their quantitative kinetics. Specifically, we employ computational strategies approaching CCSDT(Q)/CBS accuracy, combined with a dual-level strategy, to unravel the key factors governing the reaction kinetics. We find an unprecedentedly low enthalpy of activation of -5.61 kcal mol-1 at 0 K for CH2OO + HOCH2CN among CH2OO reaction with atmospheric species containing a C N group. Furthermore, we also find that the low enthalpy of activation is caused by hydrogen bonding interactions. Moreover, the present findings reveal the rate constant of CH2OO + HOCH2CN determined by loose and tight transition states has a significantly negative temperature dependence, reaching 10-10 cm3 molec.-1 s-1 close to the collisional limit at below 220 K. In addition, our findings also reveal that the rate constant of CH2OO + HOCH2CN is 103-102 times faster than that of OH + HOCH2CN below 260 K. The calculated kinetics in combination with data based on global atmospheric chemical transport model suggest that the CH2OO + HOCH2CN reaction dominates over the sink of HOCH2CN at southeast China, northern India at 1 km and in the Indonesian and Malaysian regions at 5 and 10 km. The present findings also reveal that the CH2OO + HOCH2CN reaction leads to the formation of glycolamide, which could contribution to the formation of secondary oganic aerosols.