Nitrous oxide is used as a propellant in aerosol whip cream cans. Until 1974, vinyl chloride was used in aerosol spray propellant. Both are used as propellants in aerosol sprays. The gaseous compounds may be adsorbed on the surface of the aerosol particles. Dimethyl ether is also used as a propellant in aerosol products. A vapor is different from an aerosol. This type of head is often found on the bottom of aerosol spray cans. Isobutane is also used as a propellant for aerosol cans. Many CFCs have been widely used as refrigerants, propellants (in aerosol applications), and solvents. It is distributed in liquid and aerosol forms. AWOL uses a nebulizer, a machine that agitates the liquid into an aerosol. It was identified as a stratospheric sulfate aerosol veil. The chemical constituents within the aerosol change the overall refractive index. A "monodisperse" aerosol, producible in the laboratory, contains particles of uniform size. Another data source is satellite measurements from the Stratospheric Aerosol and Gas Experiment (SAGE) program.