Cryo‐chamber simulation of stratospheric H 2 SO 4 /H 2 O particles: Composition analysis and model comparison

Abstract

The combination of a large aerosol chamber and a recently developed Aerosol Composition Mass Spectrometer (ACMS) was used to investigate sulfuric acid aerosols at low temperatures. Concentrations of condensed phase H 2 SO 4 and H 2 O 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 H 2 SO 4 /H 2 O solutions was confirmed in the composition range from 35 to 68 wt.% H 2 SO 4 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.