Proton Transfer in Mixed Clusters of Methanesulfonic Acid, Methylamine, and Oxalic Acid: Implications for Atmospheric Particle Formation

Abstract

Understanding the properties of atmospheric particles made of several components is a very challenging problem. In this paper, we perform quantum chemical calculations for small multicomponent clusters of atmospheric relevance that incorporate methanesulfonic acid (MSA), methylamine (MA), oxalic acid (OxA), and water (HO). Potential correlations between theoretical predictions of proton transfer in the small clusters and findings of recent experiments on formation of particles of detectable sizes (>2 nm) from the same components are studied. It is proposed that proton transfer from the acid to the amine in the 1:1 clusters correlates with experiments on particle formation in systems, such as MSA-MA and MSA-MA-OxA. In the case of OxA + MA, which has been observed to give few particles, proton transfer does not occur for the 1:1 cluster but does for the 2:2 cluster. Adding HO to OxA-MA promotes the occurrence of proton transfer, and corresponding particles are slightly enhanced. The partial charge on the MA component increases by adding OxA or HO to MSA-MA, which is correlated with enhanced particle formation compared to MSA-MA alone. Ab initio molecular dynamics simulations show that proton transfer at room temperature (T = 298 K) and high temperature (T = 500 K) is little affected compared with the equilibrium structure (T = 0 K). These results suggest that small cluster calculations may be useful in predicting the formation of multicomponent particles in the atmosphere.

Nanoparticles grown from methanesulfonic acid and methylamine: microscopic structures and formation mechanism

“…1. Consistent with previous studies, 57,66 the most stable structure of MSA-MA is an ion pair [H 3 CSO 3 ] À [H 3 NCH 3 ] + , where MSA transfers one proton to MA. In our previous study, we found proton transfer in the small cluster qualitatively correlates particle formation observed experimentally.…”

“…3.1 The 1 : 1 MSA-MA cluster MSA-MA, the smallest cluster, has been studied theoretically. 57,66 The geometries, bond lengths of hydrogen bonds and partial charges on MSA-MA computed at the level of PBE/cc-pVDZ are shown in Fig. 1.…”

“…S1 in ESI †). 57 For the larger systems (MSA-MA) 4 Á Á Á(MSA-MA) 4 , MSA-(MSA-MA) 4 and MA-(MSA-MA) 4 , all of the calculations were done at the level of PBE/3-21G. 86 Partial charges on each component were calculated to present the charge separation in clusters using natural bond orbital (NBO) analysis.…”

Understanding the catalytic role of oxalic acid in the SO<sub>3</sub> hydration to form H<sub>2</sub>SO<sub>4</sub> in the atmosphere

“…1993), is the water-soluble organic acid, so it has high concentration in aerosols (Kawamura et al, 2013;van Pinxteren et al, 2014;Deshmukh et al, 2016;Wang et al, 2016). In addition to accumulating in aerosols, oxalic acid, as an organic acid in the gas phase, has been found to enhance the new particle formation (NPF) (Xu et al, 2010;Weber et al, 2012;Xu and Zhang, 2012;Weber et al, 2014;Peng et al, 2015;Miao et al, 2015;Zhao et al, 2016;Chen et al, 2017;Xu et al, 2017;Arquero et al, 2017;Zhang, 2010). Theoretical studies about the effect of oxalic acid on atmospheric particle nucleation and growth have 5…”

“…shown that it can form stable complexes with water (Weber et al, 2012), sulfuric acid (Xu et al, 2010;Xu and Zhang, 2012;Miao et al, 2015;Zhao et al, 2016), ammonia (Weber et al, 2014;Peng et al, 2015) and amines (Chen et al, 2017;Xu et al, 2017;Arquero et al, 2017) via intermolecular hydrogen bond. The potential of oxalic acid for contributing to the NPF is mainly attributed to its capability of forming hydrogen bond with hydroxyl and/or carbonyl-type functional group.…”