Dependence of nucleation rates on sulfuric acid vapor concentration in diverse atmospheric locations

A simple power law model for formation rates of 1 nm particles, J₁ = K ⋠[H₂ SO₄] P, where P and K are least squares parameters, was tested for each environment. We found that, to within experimental uncertainty, P = 2.

Constraining P to 2, the prefactor K kinetic ranges from 10⁻¹⁴ to 10⁻¹¹ cm³s⁻¹. According to the nucleation theorem, an exponent value of 2 indicates that the critical cluster contains two sulfuric acid molecules. Existing nucleation rate expressions based on classical nucleation theory predict significantly larger values of P. The prefactor values vary with environment and are 1 to 4 orders of magnitude below the hard-sphere collision limit.