Interaction between Dicarboxylic Acid and Sulfuric Acid-Base Clusters Enhances New Particle Formation
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Abstract. Dicarboxylic acids are believed to stabilize pre-nucleation clusters and facilitate new particle formation in the atmosphere, but the detailed mechanism leading to the formation of multi-component critical nucleus involving organic acids, sulfuric acid (SA), base species, and water remains unclear. In this study, theoretical caculations are performed to elucidate the interactions between succinic acid (SUA) and clusters consisting of SA-ammonia (AM)/dimethylamine (DMA) in the presence of hydration of up to six water molecules. Formation of the hydrated SUASAbase clusters by adding one SUA molecule to the SAbase hydrates is energetically favorable. The addition of SUA to the SAbase hydrates either triggers proton transfer from SA to the base molecule, resulting in formation of new covalent bonds, or strengthens the pre-existing covalent bonds. The presence of SUA promotes hydration of the SAAM and SAAMDMA clusters but dehydration of the SADMA clusters. At equilibrium, the uptake of SUA competes with the uptake of the second SA molecule to stabilize the SAbase clusters at atmospherically relevant concentrations. The clusters containing both the base and organic acid are capable of further binding with acid molecules to promote their subsequent growth. Our results indicate that the multi-component nucleation involving organic acids, sulfuric acid, and base species promotes new particle formation in the atmosphere, particularly under polluted conditions.
