Atmospheric Fate of Monoethanolamine: Enhancing New Particle Formation of Sulfuric Acid as an Important Removal Process.

Monoethanolamine (MEA), a potential atmospheric pollutant from the capture unit of a leading CO capture technology, could be removed by participating HSO-based new particle formation (NPF) as simple amines. Here we evaluated the enhancing potential of MEA on HSO-based NPF by examining the formation of molecular clusters of MEA and HSO using combined quantum chemistry calculations and kinetics modeling. The results indicate that MEA at the parts per trillion (ppt) level can enhance HSO-based NPF. The enhancing potential of MEA is less than that of dimethylamine (DMA), one of the strongest enhancing agents, and much greater than methylamine (MA), in contrast to the order suggested solely by their basicity (MEA < MA < DMA). The unexpectedly high enhancing potential is attributed to the role of -OH of MEA in increasing cluster binding free energies by acting as both a hydrogen bond donor and acceptor. After the initial formation of one HSO and one MEA cluster, the cluster growth mainly proceeds by first adding one HSO, and then one MEA, which differs from growth pathways in HSO-DMA and HSO-MA systems. Importantly, the effective removal rate of MEA due to participation in NPF is comparable to that of oxidation by hydroxyl radicals at 278.15 K, indicating NPF as an important sink for MEA.