CFCs were invented about 65 years ago during a search for a new, nontoxic substance that could serve as a safe refrigerant. One of these new substances, often known by the DuPont trademark Freon, soon replaced ammonia as the standard cooling fluid in home refrigerators. It later became the main coolant in automobile air conditioners.

The 1950s and 1960s saw CFCs used in a variety, of other applications: as a propellant in aerosol sprays, in manufacturing plastics, and as a cleanser for electronic components. All this activity doubled the worldwide use of CFCs every six to seven years. By the early 1970s, industry used about a million tons every year.

Yet as recently as the late 1960s, scientists remained unaware that CFCs could affect the atmosphere. Their ignorance was not from lack of interest, but from lack of tools. Detecting the minuscule concentrations of these compounds in the atmosphere would require a new generation of sensitive detectors.

After developing such a detector, the British scientist James Lovelock, in 1970, became the first to detect CFCs in the air. He reported that one of these compounds, CFC-11, had an atmospheric concentration of about 60 parts per trillion. To put that measurement in perspective, the concentration of methane (natural gas) is 25,000 times greater. Twenty years earlier, merely detecting methane had been considered a major feat.

Lovelock found CFC-11 in every air sample that passed over Ireland from the direction of London. That was not surprising, because most major cities, including London, widely used CFCs. However, Lovelock also detected CFC-11 from air samples

Advances in Atmospheric Science and Policy Decisions Through 1996

This timeline shows the chain of events leading to prediction of the ozone depletion phenomenon, recognition of its consequences, and eventual actions to avert a threatened disaster. It is rich in examples of how basic research often contributes to unanticipated outcomes of immense societal benefit.

1840

Christian Friedrich Schönbein identifies ozone as a component of the lower atmosphere and names it.

1881

W.N. Hartley identifies ozone as the substance that absorbs ultraviolet radiation from the sun at wavelengths below 290 nanometers. He also shows that ozone resides primarily at high altitudes.

1913–1932

C. Fabry and M. Buisson show that the total amount of ozone in a vertical column of the atmosphere can be measured and that it equals (in modern units) 300 Dobson units.

1924

G.M.B. Dobson sets up a regular program of ozone measurements at Oxford with his newly developed spectrophotometer.

1930

Sydney Chapman explains how sunlight striking molecular oxygen in the atmosphere generates ozone.

1957

As part of the International Geophysical Year, four to five research stations in Antarctica begin making regular ozone measurements.

1970

The Nimbus series of satellites begins making ozone measurements.

1970

James Lovelock uses his electron capture detector to measure chlorofluorocarbons(CFCs).

1973

Richard Stolars and Ralph Cicerone disco stratospheric chlorine chain reaction.

The Ozone Depletion Phenomenon (1-8)