Contribution of methane sulfonic acid to new particle formation in the atmosphere.

Methane sulfonic acid (MSA) is present in substantial concentrations in the gas phase over oceans and coastal regions. We present an investigation into the contribution of MSA to new particle formation with the common atmospheric aerosol nucleation precursors including MSA, methanol, formic acid, acetone, dimethylether, formaldehyde, methyl formate, by making use a quantum chemical approach. Density functional theory calculations indicate that these bimolecular complexes are characterized by the presence of strong inter-molecular hydrogen bonds (SOH⋯O) with large binding energies and thermodynamic equilibrium constants. Topological analysis employing quantum theory of atoms in molecules shows that the charge density of the SOH⋯O hydrogen bonds of the MSA complexes falls in the range of hydrogen bonding criteria, but the Laplacian at bond critical points exceeds the range, which is due to the strong hydrogen bonding interactions. In all the studied complexes, the electrostatic interactions are found to be the main attractive force by localized molecular orbital energy decomposition analysis. All these indicate the environmental fate of MSA could play the role of nucleation centers in new particle formation. The effect of the atmospheric heights (0-12 km) was also considered. The Gibbs free energy of formation decreases with the increase of the atmospheric height owing to the decrease of the atmospheric temperature and pressure. The calculated Gibbs free energies of formation within the atmospheric temperature and pressure range could help to understand the atmospheric pollution.