Page 489 - Environment: The Science Behind the Stories

tHe SCieNCe beHiNd tHe StOry

discovering Ozone
depletion and the
Substances behind it

In discovering the depletion of
stratospheric ozone and coming to
understand the roles of halocarbons
and other substances, scientists
have relied on historical records, field
observations, laboratory experiments,
computer models, and satellite tech-
nology.
The story starts back in 1924,
when British scientist G.M.B. Dobson
built an instrument that measured
atmospheric ozone concentrations by Mario Molina with F. Sherwood rowland (L) and Paul Crutzen (r) upon their
sampling sunlight at ground level and receipt of the Nobel Prize
comparing the intensities of wavelengths
that ozone does and does not absorb. years earlier, British scientist James numerous researchers soon confirmed
By the 1970s, the Dobson ozone spec- Lovelock had developed an instrument that CFCs and other halocarbons were
trophotometer was being used by a to measure trace amounts of atmos- indeed depleting ozone. In response,
global network of observation stations. pheric gases and found that virtually the United States and several other
Meanwhile, atmospheric chemists all the chlorofluorocarbons (CFCs) nations banned the use of CFCs in
were learning how stratospheric ozone humanity had produced in the past aerosol spray cans in 1978. Other
is created and destroyed. Ozone and four decades were still aloft, accumu- uses continued, however, and by the
oxygen exist in a natural balance, lating in the stratosphere. early 1980s global production of CFCs
with one occasionally reacting to form This set the stage for the key was again on the rise.
the other, and oxygen being far more insight. In 1974, American chemist F. Then, a shocking new finding
abundant. Researchers found that Sherwood Rowland and his Mexican spurred the international community to
certain chemicals naturally present in postdoctoral associate Mario Molina take action. In 1985, Joseph Farman
the atmosphere, such as hydroxyl (OH) took note of all the preceding research and colleagues analyzed data from a
and nitric oxide (NO), destroy ozone, and realized that CFCs were rising into British research station in Antarctica
keeping the ozone layer thinner than the stratosphere, being broken down that had been recording ozone con-
it would otherwise be. And nitrous by UV radiation, and releasing chlorine centrations since the 1950s. Farman’s
oxide (N O) produced by soil bacteria atoms that ravaged the ozone layer team reported in Nature that springtime
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can make its way to the stratosphere (see Figure 17.24, p. 487). Molina and Antarctic ozone concentrations had
and produce NO, Dutch meteorolo- Rowland’s analysis, published in the plummeted by 40–60% just since the
gist Paul Crutzen reported in 1970. journal Nature, earned them the 1995 1970s (Figure 1a).
This last observation was important, Nobel prize in chemistry jointly with Farman’s team had beaten a group
because some human activities, such Crutzen. of NASA scientists to the punch. The
as fertilizer application, were increasing The paper also sparked discus- NASA scientists were sitting on reams
emissions of N O. sion about setting limits on CFC of data from satellites showing a global
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Following Crutzen’s report, emissions. Industry leaders attacked drop in ozone levels (Figure 1b), but
American scientists Richard Stolarski the research; DuPont’s chairman of the they had not yet submitted their analy-
and Ralph Cicerone showed in 1973 board reportedly called it “a science sis for publication.
that chlorine atoms can catalyze fiction tale . . . a load of rubbish . . . But why should an “ozone hole” be
the destruction of ozone even more utter nonsense.” But measurements localized over Antarctica, of all places?
effectively than N O can. And two in the lab and in the stratosphere by And why only in the southern spring? To
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