Quantum Chemical Study on .Cl-Initiated Atmospheric Degradation of Monoethanolamine

Recent findings on the formation of Cl in continental urban areas necessitate the consideration of Cl initiated degradation when assessing the fate of volatile organic pollutants. Monoethanolamine (MEA) is considered as a potential atmospheric pollutant since it is a benchmark and widely utilized solvent in a leading CO2 capture technology. Especially, Cl may have specific interactions with the N atom of MEA, which could make the MEA + Cl reaction have different pathways and products from those of the MEA + OH reaction. Hence, Cl initiated reactions with MEA were investigated by a quantum chemical method [CCSD(T)/aug-cc-pVTZ//MP2/6-31+G(3df,2p)] and kinetics modeling. Results show that the overall rate constant for Cl initiated H-abstraction of MEA is 5 times faster than that initiated by OH, and the tropospheric lifetimes of MEA will be overestimated by 646% when assuming that [ Cl]/[ OH] = 110% if the role of Cl is ignored. The MEA + Cl reaction exclusively produces MEA-N that finally transforms into several products including mutagenic nitramine and carcinogenic nitrosamine via further reactions with O-2/NOx, and the contribution of Cl to their formation is about 25-250% of that of OH. Thus, it is necessary to consider Cl initiated tropospheric degradation of MEA for its risk assessment.