Uptake of neutral polar vapor molecules by charged clusters/particles: Enhancement due to dipole‐charge interaction

Abstract

Recently proposed ion‐mediated nucleation theory suggests that the enhanced uptake of neutral polar molecules by the charged clusters as a result of dipole‐charge interaction may be critical to the nucleation of particles in the atmosphere. A rigorous parameterization of the enhancement effect of dipole‐charge interaction on the growth of charged clusters is presented and the important parameters controlling this enhancement factors are explored. The interaction of polar gas molecules with charges significantly enhances the growth rate of small charged clusters/particles. Polar molecules with higher dipole moment and smaller molecular size have larger enhancement factor. The enhancement factor decreases with increasing particle size and is roughly inversely proportional to temperature when the charged particles are small. At T of 300 K, the enhancement factor reaches up to 10 for the uptake of sulfuric acid molecules by ions with diameter of ∼0.5 nm but decreases quickly to 2 for uptake by a charged particle of ∼2 nm in diameter. For the uptake by molecular ions, the enhancement factor can reach as high as 20 for water molecules in the mesopause and as high as 15 for sulfuric acid in the polar stratosphere. The enhancement factors for the uptake of water dimers by charged clusters are consistently higher (up to 20–25%) than the corresponding enhancement factors for monomers. The hydration of sulfuric acid molecules in the atmosphere may affect the enhancement factor and hence ion‐mediated nucleation rate, which remains to be investigated.