An Introduction to Environmental Chemistry

tion. Attention must now turn to assisting developing countries, which still use

CFCs to switch to alternate compounds.

In the case of the halons, replacements are also being phased in. For example,

halon 1301 (bromotrifluoromethane, CF 3 Br), widely used as a fire-extinguishing

agent to protect sensitive electronic equipment, is being replaced by HFC-227

(CF 3 CHFCF 3 ), which contains no chlorine or bromine.

It is sobering to remember that despite the recent success in limiting produc-

tion of CFCs, these stable substances have a long residence time in the atmos-

phere, between 40 and 150 years. This means their effects on the stratospheric

O 3 will continue for some time after the bans on their production. Current esti-

mates suggest that the policies in place should see a decline in the stratospheric

bromine and chlorine concentrations over the next 50 years, paralleled by a rise

in ozone concentrations.

3.11 Further reading

Brimblecombe, P. (1987) The Big Smoke.Methuen, London.

Brimblecombe, P. (1996) Air Composition and Chemistry, 2nd edn. Cambridge University

Press, Cambridge.

Brimblecombe, P. & Maynard, R.L. (2001) The Urban Atmosphere and Its Effects. Imperial

College Press, London.

Elsom, D.M. (1992) Atmospheric Pollution A Global Problem.Blackwell Scientific Publica-

tions, Oxford.

Jacobson M.Z. (2002) Atmospheric Pollution. Cambridge University Press, Cambridge.

64 Chapter Three

Year

CFC-11 (ppt)

240

1980 1985 1995 2000

160

200

1990

Fig. 3.7Concentrations of CFC-11 measured at ground level, Cape Grim, Tasmania. Note

that concentrations of CFC-11 have been falling in the 1990s following the rapid increase

during the 1980s. Copyright CSIRO Australia, May 2002.