Computational Study of the Formation of Atmospheric Aerosol Precursors Under Ambient Conditions: A Case Study of the Interaction Between Sea Salt, Water, and Sulfuric Acid Molecules

Abstract

Cluster formation has significant implications in atmospheric science and environmental chemistry. These clusters are characterized by complex interactions between their constituents, which influence their structure, stability, and growth. Experimental investigations are difficult for the initial stages of prenucleation cluster formation, which leads to larger aerosols. To understand the formation of clusters, the interactions between sea salts (NaCl, KCl, and MgCl₂), water, and sulfuric acid molecules have been investigated. Each step has been comprehensively examined and thermodynamic parameters have been computed using DLPNO-CCSD(T)/CBS//M06-2X/6-311++G(3df,3pd) to find the stabilities of the molecular complexes. Among all complexes, the binding energies of cluster (SS)₁(W)₁(SA)₃ are found to be the lowest due to the formation of HCl, hydrogen bonding, and weak van der Waal forces. Sea salts have shown a more favorable interaction with H₂SO₄ compared to H₂O molecules. The addition of H₂SO₄ increases the reactivity of the cluster (SS)₁(W)_n, while the addition of H₂O molecules reduces the reactivity of the cluster (SS)₁(SA)_n. However, further addition of H₂SO₄ or H₂O to the existing cluster (SS)₁(W)_n(SA)_n increases the free energy of formation. Furthermore, the influence of temperature was also investigated, suggesting that complex formation is slightly more favorable at lower temperatures than at higher temperatures. The negative values of thermodynamic parameters indicate, that these complexes are spontaneous and exothermic over the colder regions.