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 CO2 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)1(MSA)1 cluster, followed by alternately adding one MSA and one MEA molecule, differing from the case of MA–MSA clusters.