Semiempirical H 2 SO 4 -H 2 O Cluster Standard Gibbs Reaction Energies from Nucleation Experiments: Improved Temperature Dependence.

The thermodynamics of sulfuric acid-water clusters is important for modeling new particle formation in the atmosphere. Particle number densities obtained at 296 K from a photolytic flow reactor are greatly overpredicted by the Sulfuric Acid Water Nucleation (SAWNUC) model. Empirical, temperature-dependent adjustments to the SAWNUC model allow for better agreement with the data obtained at 296 K, while maintaining reasonable agreement with the data of Hanson and Lovejoy at 242 K. Even though these adjustments result in extensive decreases in the modeled particle number densities at room temperature, the changes in the standard Gibbs reaction energies are all less than 1 kcal/mol.