Outline of why CFCs were used, what the problems are and the alternatives.

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  • CFCs
    • History of CFCs
      • They were first use in the 1930s.
      • They are chemically stable, odourless, non-toxic, non-flammable, easily compressed, have low boiling points (evaporate efficiently) and have low freezing points so they don't turn into solids very easily.
      • This makes them very useful as refridgerents.
      • Also, propellents in aerosol cans, as blowing agents for expanded polystyrene and as dry cleaning solvents.
    • The problems with CFCs
      • Some of them reached the stratosphere and began to photodissociate.
      • CCl3F + hv -> CClF + Cl
        • They are also reformed, leading to a chain reaction.
      • Huge amounts of CFCs were used, putting lots of Cl radicals into the stratosphere.
      • CFCs are estimated to have a lifetime in the troposphere of approximately 100 years.
    • Alternatives
      • HCFCs and HFCs
        • H-C bonds are broken in the troposphere before they have a chance to reach the stratosphere.
        • But are greenhouse gases
      • Alkanes
        • Do not contain chlorine
        • But are greenhouse gases


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