Cryo-chamber simulation of stratospheric H₂SO₄/H₂O particles: Composition analysis and model comparison

The combination of a large aerosol chamber and a recently developed Aerosol Composition Mass Spectrometer (ACMS) was use to investigate sulfuric acid aerosols at low temperatures. Concentrations of condensed phase H₂SO₄ and H₂O were determined with an accuracy of better than 4 wt.%. Simultaneous measurements of temperature, partial pressure of water, total sulfate amount and particle size distribution permit to calculate the particle equilibrium composition. The model description of Carslaw et al. [1995a] for H₂SO₄/H₂O solutions was confirmed in the composition range from 35 to 68 wt.% H₂SO₄ for temperatures between 188 and 236 K, extending the experimental verification to lower temperatures. Although the sub-micron particles were up to 25 K super-cooled with respect to solid sulfuric acid hydrates such as the tetrahydrate (SAT), they remained liquid for days.