Clustering of sulfuric acid, bisulfate ion and organonitrate C10H15O10N: Thermodynamics and atmospheric implications

Abstract

Abstract Recently, Highly Oxidized Molecules (HOMs) have been suggested to play an important role in New Particle Formation (NPF) in the atmosphere. Although stable clusters containing organonitrates (ONs), a common form of HOM, have been detected in both laboratory experiments and in-situ measurements, the role of ONs in their stability is still poorly understood. In this paper, we carry out a Density Functional Theory (DFT) study of the bonding of a selected C10H15O10N organonitrate, N-[2-(1,2-Dicarboxyethoxy)ethyl]-3-hydroxyaspartic acid with H2SO4 and bisulfate ion HSO4−. The present analysis reveals an important role of the C10H15O10N in the enhanced stability of ionic and, at lesser degree, neutral clusters as all the mixed dimers, trimers and tetramers containing C10H15O10N are found to be more stable compared to pure ones. The substitution of the H2SO4 molecule with the ON is particularly favorable in the case of negative ions, when the stepwise Gibbs free energy increases by up to ∼9 kcal mol−1 per step due to the presence of the ON. In particular, the free energies of the formation of (H2SO4)n-1(Organonitrate)(HSO4−) and (H2SO4)n(HSO4−) via the addition of H2SO4 differ by 0.7, 5.45 and 9.2 kcal mol−1 at n = 2, 3 and 4, respectively, in the favor of (H2SO4)n-1(Organonitrate)(HSO4−) clusters. This indicates that the C10H15O10N is capable of facilitating the production of fairly large sulfuric acid clusters and promoting in this way atmospheric NPF.