title: Size dependence of phase transitions in aerosol nanoparticles.
abstract: Phase transitions of nanoparticles are of fundamental importance in atmospheric sciences, but current understanding is insufficient to explain observations at the nano-scale. In particular, discrepancies exist between observations and model predictions of deliquescence and efflorescence transitions and the hygroscopic growth of salt nanoparticles. Here we show that these discrepancies can be resolved by consideration of particle size effects with consistent thermodynamic data. We present a new method for the determination of water and solute activities and interfacial energies in highly supersaturated aqueous solution droplets (Differential Köhler Analysis). Our analysis reveals that particle size can strongly alter the characteristic concentration of phase separation in mixed systems, resembling the influence of temperature. Owing to similar effects, atmospheric secondary organic aerosol particles at room temperature are expected to be always liquid at diameters below ~20 nm. We thus propose and demonstrate that particle size should be included as an additional dimension in the equilibrium phase diagram of aerosol nanoparticles.
authors.affiliation: Multiphase Chemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, Germany.
authors.forename: Yafang
authors.initials: Y
authors.lastname: Cheng
authors.affiliation: Multiphase Chemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, Germany.
authors.forename: Hang
authors.initials: H
authors.lastname: Su
authors.affiliation: Faculty of Chemistry, Bielefeld University, 33615 Bielefeld, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Koop
authors.affiliation: Institute of Physics, St. Petersburg State University, 198904 St. Petersburg, Russia.
authors.forename: Eugene
authors.initials: E
authors.lastname: Mikhailov
authors.affiliation: Multiphase Chemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Pöschl