DELIQUESCENCE OF SULFURIC-ACID TETRAHYDRATE FOLLOWING VOLCANIC-ERUPTIONS OR DENITRIFICATION

A thermodynamic model is employed to investigate the effects of coolin g sulfuric acid tetrahydrate (SAT) when the polar stratosphere is pert urbed by denitrification or volcanic eruptions. Also, survey experimen ts are carried out to study the plausibility of the predictions of thi s model. In contrast to an atmosphere rich in HNO3 for which Koop and Carslaw [1996] calculated that SAT deliquesces upon cooling to form a ternary solution, in a denitrified atmosphere the liquid begins to for m similar to 3 K colder, and SAT is not predicted to deliquesce comple tely above the ice frost point. Likewise, in an atmosphere with a high sulfate loading, solid/liquid aerosols are predicted to coexist over a large temperature range. For these two cases, SAT particles should t hus deliquesce only partially upon cooling, and hence, should return t o solid form upon warming. Furthermore, the results of laboratory expe riments suggest that HNO3-induced deliquescence of SAT might be too sl ow to matter even under normal stratospheric conditions.