Methanesulfonic Acid-driven New Particle Formation Enhanced by Monoethanolamine: A Computational Study.

Amines are recognized as significant enhancing species on methanesulfonic acid (MSA)-driven new particle formation (NPF). Monoethanolamine (MEA) has been detected in the atmosphere, and its concentration could be significantly increased once MEA-based postcombustion CO capture technology is widely implemented. Here, we evaluated the enhancing potential of MEA on MSA-driven NPF by examining the formation of MEA-MSA clusters using a combination of quantum chemical calculations and kinetics modeling. The results indicate that the -OH group of MEA can form at least one hydrogen bond with MSA or MEA in all MEA-containing clusters. The enhancing potential of MEA is higher than that of the strongest enhancing agent known so far, methylamine (MA), for MSA-driven NPF. Such high enhancing potential can be ascribed to not only the higher gas-phase basicity but also the role of the additional -OH group of MEA in increasing the binding free energy by forming additional hydrogen bonds. This clarifies the importance of hydrogen-bonding capacity from the nonamino group of amines in enhancing MSA-driven NPF. The main growth pathway for MEA-MSA clusters proceeds via the initial formation of the (MEA)(MSA) cluster, followed by alternately adding one MSA and one MEA molecule, differing from the case of MA-MSA clusters.