Sulfuric acid tetrahydrate SAT

Sulfuric acid tetrahydrate (SAT) also ultimately freezes out of these ternary solutions (Molina et al., 1993 Iraci et al., 1995). At higher temperatures found at higher altitudes in the middle and low latitudes, sulfuric acid monohydrate (SAM) may also be stable (Zhang et al., 1995). 

FIGURE 12.22 Composition of liquid in equilibrium with sulfuric acid tetrahydrate (SAT) as the temperature is lowered and SAT deliquesces in the presence of 5 ppm water vapor and 10 ppb HNO, at 50 m bar altitude (adapted from Koop and Carslaw, 1996). 

Sulfuric acid tetrahydrate(SAT) H2SO44H2O Fine solid crystals <1 T<213... 

From DeMore et al. (1997) and Ravishankara and Hanson (1996) and references therein. h NAT = nitric acid trihydrate (solid) SAT = sulfuric acid tetrahydrate (solid). 

These sulfuric acid particles become less concentrated as the temperature decreases or the water vapour increases. Under very cold stratospheric conditions, these liquid aerosols may take up water and HNO, forming ternary solutions H,S0/HN0,/H,0, which eventually freeze [19,24,26], Below 192 K, HNO, becomes the dominant condensed acid, and H,S04 drops to below 3 wt %. The thermodynamics and freezing nucleation of ice and H,S04 or HNO, hydrates from such solutions are however not well understood [27,28]. Other types of solid particles, such as the less stable nitric acid dihydrate (NAD, HN0,.2H,0) [29], sulfriric acid tetrahydrate (SAT, H S04.4H,0) [18,30], sulphuric acid hemihexahydrate (SAH, H2S04.6.5H20) [18], nitric acid penta-hydrate (NAP, HN03.5H,0) [31] and more complex sulfuric acid/nitric acid mixed hydrates [32] may also be a key to understanding Type IPSC nucleation and evolution [28],... 

Tables on the "reaction probalility or "uptake coefficient" have been summarized for various heterogeneous reactions in a recent review article [87], and by the IUPAC [88] and NASA-JPL [86] evaluation teams. For the purpose of this article, a rough comparison is made of the uptake rates for the reactions (1) to (5) on the different type surfaces. Three major type of surfaces have been considered a) NAT, or Type I PSC, b) Water ice, or Type II PSC and c) sulfuric acid aerosol, which is normally a liquid surface generally composed of 60-80 wt % H,S04 and 40-20 wt % H,0 also considered is the solid form SAT (sulfuric acid tetrahydrate) with a composition of 57.5 wt % H,S04. The importance of chlorine activation on sulfuric acid solutions has been demonstrated in a recent article [89]. Halogen activation on seasalt material will shortly be reviewed as part of the tropospheric processes.

Sulfuric acid tetrahydrate H2S04-4 H20 (SAT) small solid crystals T < 213 K weak... 

Solid ice Solid NAT nitrogen trihydrate Solid SAT sulfuric acid tetrahydrate Liquid SSA stratospheric sulfate aerosols Liquid STS supercooled ternary solution... 

---