Microspherules in snow and ice-fog crystals

Spherules found in snow crystals, ice-fog crystals, fallout particles, and fly ash were studied with an electron microscope using the electron diffraction method. The central part of the residues of 1004 specimens of natural snow crystals from Greenland, the United States, and Japan were examined; 14 spherules 0.1 to 1.5 μ in radius were found among them. The residues of 658 artificial ice-fog crystals formed from water vapor in flue gases of coal-burning electric power plants at Fairbanks, Alaska, were also examined; 9 spherules were found. Spherules similar to those found in ice-fog residues were found in furnace-produced fly ash fallout. Electron and optical microscope examination of spherules found in Greenland snow reveals a size distribution of the form dN/d(log r) = Cr−β where β ≈ 3. The properties of spherules and mean mass of snow crystals in Greenland are described. The electron microscope study indicated that less than 0.7% of the 1004 snow crystals contained spherules of possibly extraterrestrial origin and that snow crystals are formed mainly on clay mineral particles by heterogeneous nucleation.