The role of ammonia in sulfuric acid ion induced nucleation I. K. Ortega, T. Kurtén, H. Vehkamäki, and M. Kulmala Division of Atmospheric Sciences, Department of Physical Sciences, P.O. Box 64, FI-00014 University of Helsinki, Finland
Abstract. We have developed a new multi-step strategy for quantum chemical
calculations on atmospherically relevant cluster structures that makes
calculation for large clusters affordable with a good
accuracy-to-computational effort ratio. We have applied this strategy to
evaluate the relevance of ternary ion induced nucleation; we have also
performed calculations for neutral ternary nucleation for comparison. The
results for neutral ternary nucleation agree with previous results, and
confirm the important role of ammonia in enhancing the growth of sulfuric
acid clusters. On the other hand, we have found that ammonia does not
enhance the growth of ionic sulfuric acid clusters. The results also confirm
that ion-induced nucleation is a barrierless process at high altitudes, but
at ground level there exists a barrier due to the presence of a local
minimum on the free energy surface.
Citation: Ortega, I. K., Kurtén, T., Vehkamäki, H., and Kulmala, M.: The role of ammonia in sulfuric acid ion induced nucleation, Atmos. Chem. Phys., 8, 2859-2867, doi:10.5194/acp-8-2859-2008, 2008.