| New particle formation in the atmosphere and continuing condensational growth is a crucial secondary transformation process. The detailed knowledge on the formation mechanisms of new particles and their subsequent growth will help us to improve our understanding on the regional air pollution and global climate change. However, none of current nucleation theories can interpret well the mechanism of new particle formation. Although it is well-known that atmospheric aerosol particles contain organic species, the chemical nature of and physicochemical processes behind atmospheric nucleation involving organic acids remain unclear. In this thesis, the nucleation efficiency of 14 kinds of common organic acids were calculated and contrasted in order to confirm the most effective catalyst to nucleation. The mechanism of homogeneous nucleation enhanced by the most effectively catalyzing organic acids were studied. These calculation results would help us to improve the understanding on the mechanism of nucleation involving organic acids. Density functional theory in quantum chemistry is chosen to calculate with PW91PW91/6-311++G(3df,3pd) level of theory. The following results are obtained based on the research in this thesis.(1) Interactions of the three common atmospheric bases, ammonia (NH3), methylamine MA (CH3NH2) and dimethylamine DMA ((CH3)2NH) with H2SO4 and 14 common atmospheric organic acids (COA) (formic (CH2O2), acetic (C2H4O2), oxalic (C2H2O4), malonic (C3H4O4), succinic (C4H6O4), glutaric acid (C5H8O4), adipic (C6H10O4), benzoic (C6H5COOH), phenylacetic (C6H5CH2COOH), pyruvic (C3H4O3), fumaric acid (C4H4O4), malic (C4H6O5), tartaric (C4H6O6) and pinonic acid (C10H16O3)) have been studied. The thermodynamic stability of mixed (COA)(H2SO4), (COA)(NH3), (COA)(MA) and (COA)(DMA) dimers and (COA)(H2SO4)(NH3), (COA)(H2SO4)(MA) and (COA)(H2SO)(DMA) trimers have been investigated and their impacts on the thermodynamic stability of clusters containing H2SO4 have been studied. It has been shown that in many cases the interactions of H2SO4 with COA lead to the formation of more stable dimers than (H2SO4)2 and (C4H6O4)(H2SO4), (C6H5COOH)(H2SO4), (C6H5CH2COOH)(H2S04) and (C2H4O2)(H2SO4) are the most stable dimers. The stability of (DMA)-COA, (MA)-COA and NH3-COA complexes is not as high as that of the H2SO4 dimer. The (DMA)-COA and (MA)-COA may be combined under typical atmospheric conditions due to larger concentrations of COA compared to H2SO4. Malonic acid, succinic acid and fumaric acid are recongnized as the most efficient stabilizer for nucleating with sulfur dioxide and amine or ammonia.(2)The interactions of malonic acid and fumaric acid with amines are weaker than sulfur acid. The hydration of malonic acid and fumaric acid decreases their reactivity with amines, while the hydration of amine increase their reactivity with malonic acid and fumaric acid. The nucleation rate of malonic acid with dimethylamine is higher than malonic acid with methylamine. The stabilizing ability of malonic acid is in good agreement with fumaric acid while the concentrations of malonic acid under typical atmospheric conditions are larger than fumaric acid. So malonic acid makes more contribution in stabilizing amines than fumaric acid in atmosphere.(3)Malonic acid and Fumaric acid have significant strengthening effect on multi-component nucleation in nature. The nucleation rates of malonic acid with dimethyl-amine in multicomponent nucleation is higher than methylamine. The free energies of formation for hydrated clusters consisting of malonic acid, fumaric acid, sulfur acid and amines reveal that malonic acid and fumaric acid tend to exert a synergetic effect with amines on atmospheric aerosol nucleation. |
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