Chlorofluorocarbons (CFCs) were once used as propellants inaerosol cans, but since the Montreal Protocol was agreed to in1989, they have been replaced in nearly every country. This isbecause of the negative effects CFCs have on Earth's ozonelayer.Aerosols are now propelled by mixtures of volatile hydrocarbons,typically propane, n-butane and isobutane.Food sprays use nitrous oxide and carbon dioxide.