A3.8 Anthropogenic Influences on Ozone Depletion

Observations since the 1960s have shown that total global ozone levels have decreased by 1-2% from the maximum to the minimum of a typical cycle. However, since downward trends in ozone levels are much larger than 1-2%, particularly at the higher latitudes, the Sun’s output cannot be wholly responsible.

Man-made influences predominantly relate the manufacture and use of Ozone Depleting Substances.

Ozone Depleting Substances Include:

• Chlorofluorocarbons (CFCs) – used in refrigeration, air conditioning, and fire extinguishers.

Chlorofluorocarbons (CFCs) are a group of compounds. For example, it includes:

• Trichlorofluoromethane (CCl₃F)
• Dichlorodifluoromethane (CCl₂F₂)
• Monochloropentafluoroethane (C₂F₅Cl)
• Tetrachlorotetrafluoropropane (C₃F₄Cl₄)

• Hydrochlorofluorcarbons (HCFCs) – man made compounds not found naturally, used to replace CFCs in refrigeration, aerosol propellants, foam manufacture and air conditioning.

• Halons – used in fire extinguishers.

Halons include:

• Bromochlorodifluoromethane (CF₂ClBr)
• Bromotrifluoromethane (CF₃Br)

• Methyl Chloroform also known as (1,1,1-trichloroethane) – used as an all-purpose industrial solvent.

• Carbon Tetrachloride (the main precursor of CFCs) (CCl₄) – used as in fire extinguishers, an industrial solvent and as an agricultural fumigant.

• Methyl Bromide (CH₃Br) – used as a pesticide.

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