Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 9 12 2009 10.5194/acp-9-4031-2009 http://www.atmos-chem-phys.net/9/4031/2009/ http://www.atmos-chem-phys.net/9/4031/2009/acp-9-4031-2009.html http://www.atmos-chem-phys.net/9/4031/2009/acp-9-4031-2009.pdf 4031 4038 2009-06-18 Ammonia in positively charged pre-nucleation clusters: a quantum-chemical study and atmospheric implications A. B. Nadykto F. Yu yfq@asrc.cestm.albany.edu J. Herb Atmospheric Sciences Research Center, State University of New York at Albany, 251 Fuller Rd., Albany, NY 12203, USA The quantum-chemical treatment of pre-nucleation clusters consisting of atmospheric nucleation precursors is critically important for the understanding of the molecular nature of atmospheric nucleation. In the present study, the influence of ammonia on the thermochemical stability of positively charged pre-nucleation clusters has been studied using the Density Functional Theory (DFT). The formation of binary (NH4+)(H2O)n and ternary (NH4+)(H2SO4)(H2O)n ionic clusters and the conversion of (H3O+)(H2O)n−1 into (NH4+)(H2O)n and (H3O+) (H2SO4)(H2O)n−1 into (NH4+)(H2SO4)(H2O)n have been investigated. The thermochemical analysis carried out in the present study shows both (H3O+)(H2O)n−1→(NH4+) (H2O)n and (H2SO4)(H3O+)(H2O)n−1→(NH4+)(H2SO4) (H2O)n transformations to be favorable thermodynamically and gives us a clear indication of the important role of ammonia in the conversion of positively charged clusters containing hydronium (H3O+) into those containing protonated ammonia. Under typical continental boundary layer condition, a large fraction of small positive ions may contain ammonia, but most of neutral and negative hydrated sulfuric acid monomers do not contain ammonia. In term of absolute concentrations, around 1000 cm−3 out of 107 cm−3 of sulfuric acid momoners contain ammonia. (NH4)+(H2O)n clusters appear to dominate the concentrations of small positive ions. Because of the weak affinity of sulfuric acid molecules to (H3O+)(H2O)n and (NH4+)(H2O)n ions (n≤6), the concentrations of both ammoniated and un-ammoniated sulfuric acid water proton clusters are quite low. The atmospheric implications of the obtained results are discussed. % vor jede Referenz Ball, S. M., Hanson, D. R., Eisele, F. L., and McMurry, P. H.: Laboratory studies of particle nucleation: Initial results for H2SO4, H2O, and NH3 vapors, J. Geophys. Res., 104, 23709–23718, 1999. Christensen, P. S., Wedel, S., and Livbjerg, H.: The kinetics of the photolytic production of aerosols from SO2 and NH3 in humid air, Chem. Eng. Sci., 49, 4605–4614, 1994. Ding, C.-G., Laasonen, K., and Laaksonen, A.: Two sulfuric acids in small water clusters, J. Phys. Chem. A., 107(41), 8648–8662, 2003. Froyd, K. D. and Lovejoy, E. R.: Experimental thermodynamics of cluster ions composed of H2SO4 and H2O. 1. Positive ions, J. Phys. Chem. A, 107, 9800–9811, 2003. 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