Atmospheric Initial Nucleation Containing Carboxylic Acids.

The possible involvement of chemical components in atmospheric new particle formation has received increased attention in recent years. However, the deep understanding of the clusters formed between atmospheric gas-phase organic acids is incomplete. In this work, the chemical and physical properties of the cluster formed between three organic acids [glyoxylic acid (GA), oxalic acid (OA), and pyruvic acid (PA)] with common atmospheric nucleation precursors [methyl hydrogen sulfate (MHS), methanesulfonic acid (MSA), and hydroxymethanesulfonic acid (HMSA)] have been investigated with density functional theory and ab initio coupled-cluster singles and doubles with perturbative triples (CCSD(T)) theory. Six- to nine-membered cyclic ring structures are mainly arranged via two classes of intermolecular hydrogen bonds: SO-H···O and CO-H···O. The GA/OA/PA-MHS/MSA/HMSA complexes with the nine- and eight-membered cyclic ring structures are thermodynamically more stable than the others. Large red shifts of the OH-stretching vibrational frequencies of both SO-H···O (354-794 cm-1) and CO-H···O (320-481 cm-1) are obtained with regard to the isolated gas monomers. Atoms in molecules topological analysis reveals that the Laplacian of the charge density of the bimolecular interactions in the GA/OA/PA-MHS/MSA/HMSA complexes is higher than the upper value of the hydrogen bond criteria. The thermodynamic data, dipole moments, and atmospheric mixing ratios indicate that the MHS- and MSA-containing complexes possibly take part in atmospheric new particle formation. Additionally, the environmental factors, such as temperature and pressure, are also important in atmospheric particle nucleation, and the gas-mixing ratios of the clusters at 12 km are much enhanced by 18-44 times with respect to the ones at the ground level. This study suggests that small cluster calculations may be helpful in simulating atmospheric new particle formation.