Structure of Liquid H2SO4 — H2O Clusters Around Ions: Thermodynamic Theory
The example of H2SO4–H2O clusters was taken because of its importance for air pollution problems. H2SO4 is formed by photo-oxidation from the primary pollutant SO2 by gas-to-particle conversion in the atmosphere. Ionized H2SO4 – H2O clusters are expected to be observed in polluted city air (Cox, 1974). Furthermore H2SO4 – H2O droplets were identified in background atmosphere near Antarctica (Mészdros, 1974), in dependence of the available NH3-concentration.
In this paper it was calculated by how many H2O-molecules and H2SO4-molecules a single-charged ion is surrounded at 25°C for various relative humidities (RH ≤ 100%) and various activities of sulfuric acid vapor (5 × 10–3 to 1 × 10–5) using the Becker-Flood-Doyle theory of the heteromolecular homogeneous nucleation for stable clusters.
The size and composition is given by the minimum of the droplet formation free energy, dependent on the concentrations of gaseous H2O and H2SO4 vapors in the atmosphere. The cluster composition (400–700 pm in size) is shifted to a larger number of H2O-molecules with increasing RH at nearly constant H2S04-concentration.
The calculated cluster concentration for pure ion-water molecules is compared with the experiment and showed good agreement. The aim of this paper is to predict results of future experiments on the structure of binary mixture droplets around ions. This comparison would test how good the classical thermodynamic theory describes aerosol particles in the range of hundreds of picometers despite using macroscopic concepts (i.e. surface tension).
KeywordsAbsolute Minimum Stable Cluster Noctilucent Cloud Cluster Composition Cluster Concentration
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