Environmental Engineering Reference
In-Depth Information
Figure 7.10
Greenhouse gas contributions to global warming (a) 1880-1980 (b) 1980s
Source:
After Mintzer (1992)
that there are sources yet to be identified (Watson
et al.
1990). As a result the global N
2
O budget
remains poorly understood, and its future
concentration is therefore difficult to predict.
CFCs and other halocarbons released from
refrigeration units, insulating foams, aerosol
spray cans and industrial plants are recognized
for their ability to destroy the stratospheric ozone
layer, but they are also among the most potent
greenhouse gases. For example, CFC-11 is about
12,000 times more effective than CO
2
(Houghton
et al.
1990). The CFCs are entirely anthropogenic
in origin, and should therefore be much easier to
monitor and control than some of the other gases.
Their concentrations in the atmosphere range
from CFC-115 at 5 parts per trillion by volume
(pptv) to CFC-12 at 484 pptv, and have been
growing at rates between 4-10 per cent per
annum. Other halocarbons, such as Halon-1211
and Halon-1301, used mainly in fire
extinguishers, with current concentrations of less
than 2 pptv are growing at rates as high as 15
per cent per year (Watson
et al.
1990). Recent
international agreements to reduce the use of
