Environmental Engineering Reference
In-Depth Information
Technical Note
.
: Other Greenhouse Gases
Methane is the second most important greenhouse gas after
carbon dioxide, as shown in
Table
. It is the natural gas
used in power plants and home heating, and is also produced
by some biological processes. It is a much stronger green-
house gas than CO
.
because it easily absorbs the reradiated
heat from the Earth over a broader energy band than CO
or
water vapor. It has increased in the atmosphere from about
.
ppm to about
ppm and even at this very low level
contributes about
% to today
'
s climate change. Although
its lifetime is only
years, its action is so powerful that it
has to be carefully controlled. There is more about this in
Chapter
.
Tropospheric ozone is next on the list. This is not the
ozone of the Antarctic
but that produced in
the lower atmosphere by the interaction of sunlight on
ordinary smog, mainly that from automobiles. The short
lifetime of this material means that it does not have time to
mix through the entire atmosphere, but mainly exists in
plumes downwind from large cities. Even though it is not a
“
“
ozone hole,
”
effect, its impact on the average temperature
increase is important.
Nitrous oxide is also a more powerful greenhouse gas than
carbon dioxide. Its preindustrial era concentration was less
than about
whole Earth
”
.
ppm. It has increased by only about
%to
date, but even that is signi
cant. Some is produced naturally,
and the increase comes from microbial interaction with the
huge amount of nitrogen fertilizers used in farming, and
from some chemical processes. Its
-year lifetime means
we have to pay attention to it.
Fluorocarbons have a
-year lifetime and could have
become a serious problem. However, the Montreal Treaty
(
uorocar-
bons, which was made to close the Antarctic ozone hole, has
dramatically reduced its release into the atmosphere. The
(final version in
) to phase out production of
