Page 490 - Environment: The Science Behind the Stories

determine what was causing this odd By 1987, the mass of scientific 500
phenomenon, atmospheric chemists evidence helped convince the world’s 1987
Susan Solomon, James Anderson, nations to agree on the Montreal 400 2008
Crutzen, and others mounted expedi- Protocol, which aimed to cut CFC
tions in 1986 and 1987 to analyze production in half by 1998. Within 300
atmospheric gases using ground stations two years, further scientific evidence Ozone depletion potential (kilotons/year)
and high-altitude balloons and aircraft. and computer modeling showed that 200
From their data they figured out how the more drastic measures were needed. 100
region’s polar stratospheric clouds and In 1990, the Montreal Protocol was
circulating winds provide ideal conditions strengthened to include a complete 0
for chlorine from CFCs and other chemi- phaseout of CFCs by 2000, in the N 2 O Ozone-depleting
cals to set in motion the destruction of first of several follow-up agreements. substances being
massive amounts of ozone. Today, amounts of ozone-depleting phased out
Figure 2 Since most ozone-depleting
substances were phased out begin-
350 September ning in 1987, nitrous oxide (N O; left
Ozone levels (Dobson units) 250 Farman depleting substance we emit. It has less
2
bar) has become the primary ozone-
October
300
impact than CFCs and other halocar-
bons did in 1987 (full-bar values), but
more impact than any other substance
200
today (lower portion of bars). Adapted
150
oxide (N O): The dominant ozone-depleting
2
paper
substance emitted in the 21st century. Science
100 et al. from Ravishankara, A.R., et al., 2009. Nitrous
1955 1965 1975 1985 1995 2005 2015 326: 123–125, Fig 1. Reprinted by permission of
Year AAAS and the author.
(a) Monthly mean ozone levels at Halley, Antarctica

310 substances in the stratosphere are
Nimbus 7 Meteor 3 Earth probe
TOMS TOMS NOAA 9 TOMS OMI beginning to level off.
Ozone (Dobson units) 290 research. In 2009, a team led by CHAPTER 17 • AT m os PHER i C sC i E n CE , Ai R Qu A li T y, A nd Poll u T i on Con TR ol
As the ozone layer begins a long-
300
SBUV/2
term recovery, scientists continue their
A.R. Ravishankara of the National
Oceanic and Atmospheric Adminis-
Farman
280
et al.
(N O) had now become the leading
paper tration determined that nitrous oxide
2
cause of ozone depletion (Figure 2).
270
1980 1985 1990 1995 2000 2005 2010 Its emissions are not regulated, so
Year its impacts have come to surpass
those that the remaining halocarbons
(b) Global ozone readings from 5 satellites
currently exert. Ravishankara’s team
Figure 1 Monitoring shows ozone depletion. Data from Halley, Antarctica (a), show a points out that regulating nitrous
decrease in stratospheric ozone concentrations from the 1960s to 1990. Once ozone- oxide, which is also a potent green-
depleting substances began to be phased out, ozone concentrations stopped declining. house gas, would help mitigate cli-
Ozone decline and stabilization are also evident globally (b), as seen in data from five mate change as well as speed ozone
satellites. Data from (a) British Antarctic Survey; and (b) NASA. recovery.

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