Valine involved sulfuric acid-dimethylamine ternary homogeneous nucleation and its atmospheric implications

Abstract New Particle Formation (NPF) is considered as the dominant source of aerosol particles, influencing the environment and human health tightly. In recent years, valine (VAL) has been identified in field detection in urban areas, which reveals that VAL may play an important role in participating in atmospheric nucleation. However, there have been no categorical reports explaining how VAL participates in the multi-component nucleation with precursor Sulfuric Acid (SA) and the atmospheric organic amine Dimethylamine (DMA) so far. In this paper, quantum chemical calculation and cluster kinetic simulation have been studied to research the nucleation mechanism of (SA)x(DMA)y(VAL)z (0≤x, y, z≤3) system. Structural and thermodynamic analysis at ωB97XD/6-31++G(d, p) theory level and basis set shows that VAL could form various stable structures through hydrogen bonds with SA and DMA, and proton transfer in ternary structure enhances the stability of system. However, in the clusters of SA-DMA-VAL system with large numbers of molecules, there has been steric hindrance between molecules of cluster due to the high proportion of inactive groups in VAL, which insulates the further formation of hydrogen bonds. With regard to the distribution of Gibbs free energy on VAL-DMA grid, the energy decreases rapidly along the diagonal with VAL and DMA in different numbers of SA molecules, predicting possible nucleation path along the diagonal. Besides, there is a synergistic effect of VAL in system SA-DMA-VAL, and VAL tends to replace the role of DMA in the ternary system. Evaporation rate analysis indicates that the ternary system containing SA is more stable. The simulating formation rate of SA-DMA-VAL system compared with the CLOUD experiment at CERN shows that the nucleation potential of SA-DMA-VAL is superior to that of SA-NH3-H2O, but inferior to that of SA-DMA-H2O, inferring that VAL may show more potential in growth processes than the initial nucleation processes in the light of the specific value of formation rate.