AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Equilibrium Size Distributions of Neutral and Negatively Charged Sulfuric Acid-Water Clusters from Self-Consistent Thermodynamic Tables
JAMISON A. SMITH, Karl D. Froyd, Owen B. Toon, University of Colorado
Abstract Number: 509 Working Group: Aerosol Nucleation: From Clusters to Nanoparticles
Abstract We are interested in creating a thermodynamic database of the association reactions for molecules involved in the nucleation of new atmospheric particles. We start with the simplest system of sulfuric acid and water, with the idea that once we have a framework for this simple system, the framework can be expanded to include other pertinent molecules.
Tables of reaction enthalpies and entropies are constructed from existing experimental measurements, quantum chemical calculations and classical thermodynamic models. Initially, this two-dimensional patchwork of Gibbs free energy is not self-consistent. For example, the Gibbs energy of formation of a cluster containing two water molecules and one sulfuric acid molecule depends on the path taken: associate two waters and then associate the acid or associate one water and one acid and then associate the second water. We enforce self-consistency on the Gibbs free energy surface by assuming a correction exists for every association reaction, and the corrections are minimized via the method of Lagrange multipliers. As such, self-consistent Gibbs free energy surfaces have been generated for the neutral clusters and the negative ion clusters.
Once the Gibbs free energy surfaces are self-consistent, the equilibrium size distributions for neutral and negative ion clusters are solved simultaneously for a variety of atmospheric conditions. In addition, energy barriers to nucleation are presented for the neutral and negative ion clusters for various atmospheric conditions.