Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 9 1 2009 10.5194/acpd-9-4231-2009 http://www.atmos-chem-phys-discuss.net/9/4231/2009/ http://www.atmos-chem-phys-discuss.net/9/4231/2009/acpd-9-4231-2009.html http://www.atmos-chem-phys-discuss.net/9/4231/2009/acpd-9-4231-2009.pdf 4231 4249 2009-02-09 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+)(H2OSO4)(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 positive sulfuric acid monomer ions may contain ammonia. 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