Comparison results of eight oxygenated organic molecules: Unexpected contribution to new particle formation in the atmosphere

Recently, the correlation between the new particle formation (NPF) events and oxygenated organic molecules (OMs) was observed frequently in forest ambient. However, the understanding of OMs-driven NPF mechanism at the molecular level remains ambiguous. The participation of eight organic compounds (Orgs) together with sulfuric acid (SA) respectively in the initial steps of NPF was investigated by the quantum-chemical calculation and Atmospheric Cluster Dynamics Code (ACDC). Thermodynamic and structural analysis prove that most of (Org)x(SA)y (0 ≤ x ≤ 2; 0 ≤ y ≤ 2) clusters possess stable H-bonds, but other interactions, such as steric hindrance, should not be ignored when investigating their stabilities and reaction properties. Furthermore, the cluster formation rates of eight Org-SA systems are calculated and found to be different at three levels: (1) systems involved 3-carboxyheptanoic acid (CHA) and phthalic acid (PTA) present high formation rates exceeding 10−3 cm3 s−1, which indicate their high nucleation abilities; (2) systems containing cis-3-caric acid (CRA), limonic acid (LMA) and 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA) have medium formation rate values from 10−6 to 10−4 cm3 s−1; and (3) systems including cis-pinic acid (PNA), 2-methyltetrols (MT) and 2-methylglyceric acid (MGA) present low formation rates less than 10−8 cm3 s−1. Our comparison results of theoretical researches about eight Orgs and SA indicate that OMs are expected to make important contributions to NPF under real atmospheric conditions. Especially, CHA and PTA, the crucial oxidation product of monoterpene and aromatic respectively, represent considerably strong potential abilities to form the critical clusters unexpectedly, and more attention should be paid to their effects on NPF in the real environment.