Ice condensation on sulfuric acid tetrahydrate: Implications for polar stratospheric ice clouds

[摘要] The mechanism of ice nucleation to formType 2 PSCs is important for controlling the ice particle size and hence the possible dehydration in the polar winterstratosphere.This paper probes heterogeneous ice nucleation on sulfuric acidtetrahydrate (SAT).Laboratory experiments were performed using a thin-film, high-vacuumapparatus in which the condensed phase is monitored via Fourier transform infrared spectroscopy and water pressure is monitored with the combination of an MKSbaratron and an ionization gauge.Results show that SAT is an efficient ice nucleus witha critical ice saturation ratio of S*_ice = 1.3 to 1.02 over the temperature range169.8-194.5 K.This corresponds to a necessary supercooling of 0.1-1.3 K below the ice frost point.The laboratory data is used as input for a microphysical/photochemical model toprobe the effect that this heterogeneous nucleation mechanism could have onType 2 PSC formation and stratospheric dehydration.In the model simulations, even a very smallnumber of SAT particles (e.g., 10^-3 cm^-3) result in ice nucleation on SAT as the dominantmechanism for Type 2 PSC formation.As a result, Type 2 PSC formation is morewidespread, leading to larger-scale dehydration.The characteristics of the clouds arecontrolled by the assumed number of SAT particles present, demonstrating that a propertreatment of SAT is critical for correctly modeling Type 2 PSC formation andstratospheric dehydration.

[学科分类] 大气科学