Theoretical Investigation of Interaction of Dicarboxylic Acids with Common Aerosol Nucleation Precursors

Dicarboxylic acids are important products from photo-oxidation of volatile organic compounds and are believed to play an important role in the formation and growth of atmospheric secondary organic aerosols. In this paper, the interaction of five dicarboxylic acids, i.e., oxalic acid (C2H2O4), malonic acid (C3H4O4), maleic acid (C4H4O4), phthalic acid (C8H6O4), and succinic acid (C4H6O4), with sulfuric acid and ammonia has been studied, employing quantum chemical calculations, quantum theory of atoms in molecules (QTAIM), and the natural bond orbital (NBO) analysis methods. Several levels of quantum chemical calculations are considered, including coupled-cluster theory with single and double excitations with perturbative corrections for the triple excitations (CCSD(T)) and two density functionals, B3LYP and PW91PW91. The free energies of formation of the heterodimer and heterotrimer clusters suggest that dicarboxylic acids can contribute to the aerosol nucleation process by binding to sulfuric acid and ammonia. In particular, the formation energies and structures of the heterotrimer clusters show that dicarboxylic acids enhance nucleation in two directions, in contrast to monocarboxylic acids.