Structural Effects of Amines in Enhancing Methanesulfonic Acid-Driven New Particle Formation

Abstract

Atmospheric amines can enhance methanesulfonic acid (MSA)-driven new particle formation (NPF), but the mechanism is fundamentally different compared to the extensively studied sulfuric acid (SA)-driven process. Generally, the enhancing potentials of amines in SA-driven NPF follow the basicity, while this is not the case for MSA-driven NPF, where structural effects dominate making MSA-driven NPF more prominent for methylamine (MA) compared to dimethylamine (DMA). Therefore, probing structural factors determining the enhancing potentials of amines on MSAdriven NPF is key to fully understanding the contribution of MSA on NPF. Here, we performed a comparative study on DMA and MA enhancing MSA-driven NPF by examining cluster formation using computational methods. The results indicate that DMA-MSA clusters are more stable than the corresponding MA-MSA clusters for cluster size up to (DMA)2(MSA)2, indicating that the basicity of amines dominates the initial cluster formation. The methyl groups of DMA were found to present significant steric hindrance beyond the (DMA)2(MSA)2 cluster and this adds to the lower hydrogen bonding capacity of DMA making the cluster growth less favorable compared to MA.This study implies that several amines could synergistically enhance MSA-driven NPF by maximizing the advantage of different amines in different amine-MSA cluster growth stages.

A predictive model for salt nanoparticle formation using heterodimer stability calculations

“…We specifically investigate the use of pK a in comparison to gas-phase acidity measures to predict proton transfer in the heterodimer as well as heterodimer stability. In addition, we examine if base vapor pressure has any correlation with heterodimer stability, as sulfuric acid is often cited to participate in NPF because of its low volatility and condensation onto clusters (Weber et al, 1996;Ball et al, 1999;Sipilä et al, 2010). Finally, we also calculate the dipole moment and polarizability of the studied base molecules to see if, in the absence of ions, they have any predictive capability of heterodimer stability.…”

The Role of Organic Acids in New Particle Formation from Methanesulfonic Acid and Methylamine

“…A multi-step sampling scheme was used to search for the global minima structures of the 12 (MA)1(MSA)1(OA)1 clusters, as well as the larger (MSA)x(MA)y(OA)z (0 ≤ y ≤ x+z ≤ 3) clusters. The binary MSA-MA cluster structures were taken from our previous work (Shen et al, 2020). Details of the scheme can be found in our previous studies addressing atmospheric cluster formation (Shen et al, 2019;Shen et al, 2020;Xie et al, 2017;Ma et al, 2019a).…”

“…The binary MSA-MA cluster structures were taken from our previous work (Shen et al, 2020). Details of the scheme can be found in our previous studies addressing atmospheric cluster formation (Shen et al, 2019;Shen et al, 2020;Xie et al, 2017;Ma et al, 2019a). Briefly, around 1000-10000 initial configurations for each cluster were randomly generated, and subsequently underwent a gradual screening process using various theoretical methods, to locate the clusters lowest in free energy.…”

“…Atmospheric bases can enhance both SA-driven and MSA-driven NPF by stabilizing freshly formed molecular clusters via acid-base proton transfer reactions (Zhang et al, 2012;Almeida et al, 2013;Chen et al, 2020b;Perraud et al, 2020b;Perraud et al, 2020a;Kurten et al, 2008;Loukonen et al, 2010;Glasoe et al, 2015;Olenius et al, 2017;Ma et al, 2019b;Zuo et al, 2021;Shen et al, 2020;Shen et al, 2019;Chen et al, 2020a;Xu et al, 2020;Nishino et al, 2014). Amines have been shown to be much more efficient stabilizing species compared to ammonia for both SA-base and MSA-base cluster formation (Almeida et al, 2013;Kurten et al, 2008;Chen et al, 2020b;Perraud et al, 2020a;Shen et al, 2020;Chen et al, 2016). However, even considering the enhancing effect of bases, the SA-driven and MSA-driven nucleation mechanism still underestimates the nucleation rates compared to field observations (Zhang et al, 2012;Lee et al, 2019).…”

“…CC BY 4.0 License. molecular structure (Shen et al, 2020;Shen et al, 2019). In addition, there is a large difference in atmospheric abundance of various OAs which also has an influence on the relative importance of different OAs in MSA-amine-OA cluster formation.…”