text: The halomethanes are produced on an industrial scale from abundant precursors such as natural gas or methanol, and from halogens or halides. They are usually prepared by one of three methods.
  *Free radical chlorination of methane (under ultraviolet light):
  This method is useful for the production of  (n = 1, 2, 3, or 4). The main problems with this method are that it cogenerates HCl and it produces mixtures of different products. Using  in large excess generates primarily  and using  in large excess generates primarily , but mixtures of other products will still be present.
  *Halogenation of methanol. This method is used for the production of the mono-chloride, -bromide, and -iodide.
  *Halogen exchange. The method is mainly used to produce fluorinated derivatives from the chlorides.
  *Reaction of methane with hypochlorous acid, producing water.
  *Reaction of methanol with hypochlorous acid, producing hydrogen peroxide.
  Traces of halomethanes in the atmosphere arise through the introduction of other non-natural, industrial materials.