Contribution of Methanesulfonic Acid to the Formation of Molecular Clusters in the Marine Atmosphere

Because of the lack of long-term
measurements, new particle formation
(NPF) in the marine atmosphere remains puzzling. Using quantum chemical
methods, this study elucidates the cluster formation and further growth
of sulfuric acid–methane­sulfonic acid–dimethylamine
(SA-MSA-DMA) clusters, relevant to NPF in the marine atmosphere. The
cluster structures and thermochemical parameters of (SA)n(MSA)m(DMA)l (n + m ≤
4 and l ≤ 4) systems are calculated using
density functional theory at the ωB97X-D/6-31++G(d,p) level
of theory, and the single-point energies are calculated using high-level
DLPNO-CCSD(T0)/aug-cc-pVTZ calculations. The calculated
thermochemistry is used as input to the Atmospheric Cluster Dynamics
Code (ACDC) to gain insight into the cluster dynamics. At ambient
conditions (298.15 K, 1 atm), we find that the distribution of outgrowing
clusters primarily consists of SA and DMA, with a minor contribution
from the mixed SA–MSA–DMA clusters. At lower temperature
(278.15 K, 1 atm) the distribution broadens, and clusters containing
one or more MSA molecules emerge. These findings show that in the
cold marine atmosphere MSA likely participates in atmospheric NPF.