Estudos teóricos de moléculas orgânicas na formação de aerossóis atmosféricos

Abstract

The presence of aerosols in the atmosphere is considered to be one of the factors responsible for the climate changes occurring around the world. There is a consensus that the formation of atmospheric aerosols (AA's) initiates from the interactions between certain atmospheric molecules like H2SO4 and H2O, collectively called as atmospheric nucleation precursors (ANP) forming hydrogen-bonded molecular clusters. However, there exist doubts about the exact composition of these molecular clusters, the nature of the intermolecular interactions and the contributions of different components, mainly organic molecules, in strengthening and growth of these clusters leading to the formation of new particles. In the present work, we applied DFT-based quantum-chemical models and classical simulation to investigate the interactions of MSA and some amino acids with ANP's. The work was developed in the gas phase, which is important to understand the initial process of formation of AA's, then in the presence of water molecules, which is important regarding the formation of cloud condensation nuclei and, finally, we analyze the spatial distribution and free energy of solvation of amino acids like glycine, alanine and valine. The hydrogen bonds were characterized using energetic and vibrational spectroscopic parameters along with the tools of quantum theory of atoms in molecules. Analyses of the binding energies of the clusters indicate that MSA indeed brings additional stability to the clusters with H2SO4 and the lower temperatures and pressures at higher altitudes of the troposphere favor the formation of MSA(H2SO4)n clusters. Analyses of the electronic properties show that the elastic scattering of light increases many times when it interacts with the clusters. The simulation of the solvent effect demonstrated the capacity of these clusters to condense water on their surfaces. Extending the solvation analysis to the amino acids we observe that the three amino acids considered for this work showed difference in their distribution inside the solvent, with valine having greater presence at the air-water interface, followed by alanine and finally glycine, whose free energy indicates a preference for the bulk region.