THE UNSUITABILITY OF METEORITIC AND OTHER NUCLEI FOR POLAR STRATOSPHERIC CLOUD FREEZING

Bulk freezing experiments have been performed with binary and ternary HNO3/H2SO4/H2O solutions containing original micrometeorites, ground s amples of representative larger meteorites and other freezing nuclei o f potential stratospheric importance. The experiments enable us to det ermine upper bounds for the heterogeneous freezing rates of sulfuric a nd nitric acid hydrates. Based on an analysis, of the meteoritic mass flux from space and of the modifications meteorites undergo when enter ing the atmosphere, the resulting morphology and surface area of extra terrestrial material in the stratosphere are estimated. From this micr ometeorites gained from Antarctica are shown to be a good proxy for me teoritic surfaces in the stratosphere. In combination with this analys is the freezing experiments suggest that heterogeneous nucleation rate s on micrometeorites ale too low to enhance freezing of polar stratosp heric clouds above the frost point.