Environmental Engineering Reference
In-Depth Information
Ozone-Depleting Substances and the Thinning of the
Ozone Layer
By the time Arctic Monitoring and Assessment Programme (AMAP) was established in
1991, it was well known that the ozone layer had dramatically thinned (been depleted) over
the previous decade and a half. The cause had been identified and international actions to
arrest the depletion had also begun under the Montreal Protocol, a brand-new treaty we will
learn more about a little later. In support of the protocol, the World Meteorological Organ-
ization (WMO) and the United Nations Environment Programme (UNEP) produce period-
ic assessments of ozone depletion and on its associated environmental effects. These as-
sessments, together with two assessments from AMAP, have provided most of the material
for this chapter. The two AMAP reports were prepared by teams led by Elizabeth (Betsy)
Weatherhead. The first was included in chapter 11 of the 1998
Assessment Report: Arc-
tic Pollution Issues
. The second appeared as chapter 5 in the 2005
Arctic Climate Impact
Assessment
.
Concernfortheintegrity oftheozonelayerbeganinthelate1960s.Thiswasinrelation
to the possible environmental impacts of the engines of the space shuttle in the stratosphere
and of a planned fleet of civil supersonic transports (SSTs). In 1970, Dutch chemist Paul
Crutzen showed that the nitrogen oxides NO and NO
2
(collectively abbreviated as NOx)
formed bysoil microorganisms could reach the stratosphere. There, they react with free oxy-
gen atoms, thus slowing the creation of ozone (O
3
) and also decomposing ozone into nitro-
gen dioxide (NO
2
) and oxygen gas (O
2
). What is more, this reaction did not involve the loss
of NO and NO
2
, which were functioning as catalysts. Harold Johnston then published a pa-
per in
Science
in 1971 in which he specifically linked the potential impact of NOx erosion
of the ozone layer to the planned operation of a fleet of SSTs. By this time, plans to devel-
op a fleet of SSTs in the United States had been abandoned, but the proposal had awakened
scientific interest in the health of the ozone layer.
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