New Parameterizations for Neutral and Ion‐Induced Sulfuric Acid‐Water Particle Formation in Nucleation and Kinetic Regimes

We have developed new parameterizations of electrically neutral homogeneous and ion‐induced sulfuric acid‐water particle formation for large ranges of environmental conditions, based on an improved model that has been validated against a particle formation rate data set produced by Cosmics Leaving OUtdoor Droplets (CLOUD) experiments at European Organization for Nuclear Research (CERN). The model uses a thermodynamically consistent version of the Classical Nucleation Theory normalized using quantum chemical data. Unlike the earlier parameterizations for H2SO4‐H2O nucleation, the model is applicable to extreme dry conditions where the one‐component sulfuric acid limit is approached. Parameterizations are presented for the critical cluster sulfuric acid mole fraction, the critical cluster radius, the total number of molecules in the critical cluster, and the particle formation rate. If the critical cluster contains only one sulfuric acid molecule, a simple formula for kinetic particle formation can be used: this threshold has also been parameterized. The parameterization for electrically neutral particle formation is valid for the following ranges: temperatures 165–400 K, sulfuric acid concentrations 104–1013cm−3, and relative humidities 0.001–100%. The ion‐induced particle formation parameterization is valid for temperatures 195–400 K, sulfuric acid concentrations 104–1016cm−3, and relative humidities 10−5–100%. The new parameterizations are thus applicable for the full range of conditions in the Earth's atmosphere relevant for binary sulfuric acid‐water particle formation, including both tropospheric and stratospheric conditions. They are also suitable for describing particle formation in the atmosphere of Venus. Our H2SO4‐H2O parameterizations reproduce state‐of‐the‐art experimental and theoretical results for large ranges of environmental conditionsWe recommend replacing Vehkamäki et al. (2002, 2003) neutral particle formation parameterizations with ours and adding the ion‐induced pathwayCombination of neutral and ion‐induced pathways and the kinetic regime is required to describe H2SO4particle formation on Earth and Venus