Geology Reference
In-Depth Information
extremely acute as atmospheric chemistry (beyond major component
ratios) only became a matter of serious scientific study in the 1950s.
There are two major reasons why environmental chemistry has flourished
as a discipline only rather recently. Firstly, it was not previously perceived
as important. If environmental chemical composition is relatively invariant
in time, as it was believed to be, there is little obvious relevance to
continuing research. Once, however, it is perceived that composition is
changing (e.g. CO
2
in the atmosphere;
137
Cs in the Irish Sea) and that such
changes may have consequences for humankind, the relevance becomes
obvious. The idea that using an aerosol spray in your home might damage
the stratosphere, although obvious to us today, would stretch the credulity
of someone unaccustomed to the concept. Secondly, the rate of advance
has in many instances been limited by the available technology. Thus, for
example, it was only in the 1960s that sensitive reliable instrumentation
became widely available for measurement of trace concentrations of metals
in the environment. This led to a massiveexpansioninresearchinthisfield
and a substantial downward revision of agreed typical concentration levels
due to improved methodology in analysis. It was only as a result of James
Lovelock's invention of the electron capture detector that CFCs were
recognised as minor atmospheric constituents and it became possible to
monitor increases in their concentrations (see Table 1). The table exempli-
fies the sensitivity of analysis required since concentrations are at the ppt
level (1 ppt is one part in 10
12
by volume in the atmosphere) as well as the
substantial increasing trends in atmospheric halocarbon concentrations, as
measured up to 1990. The implementation of the Montreal Protocol, which
requires controls on production of CFCs and some other halocarbons, has
led to a slowing and even a reversal of annual concentration trends since
1992 (see Table 1).
Table 1 Atmospheric halocarbon concentrations and trends
a
Concentration (ppt)
Annual change (ppt)
Halocarbon
Pre-industrial
2000
To 1990
1999-2000
Lifetime (years)
CCl
3
F (CFC-11)
0
261
þ
9.5
1.1
50
CCl
2
F
2
(CFC-12)
0
543
þ
16.5
þ
2.3
102
CClF
3
(CFC-113)
0
3.5
400
C
2
Cl
2
F
4
(CFC-113) 0
82
þ
4-5
0.35
85
C
2
Cl
2
F
4
(CFC-114) 0
16.5
300
C
2
ClF
5
(CFC-115)
0
8.1
þ
0.16
1700
CCl
4
0
96.1
þ
2.0
0.94
42
CH
3
CCl
3
0
45.4
þ
6.0
8.7
4.9
a
Data from: World Meteorological Organization, Scientific Assessment of Ozone Depletion: 2002,
WHO, Geneva, 2002.
