Environmental Engineering Reference
In-Depth Information
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Halons
are used in fire suppression and dry-cleaning supplies. Halons also are found naturally in the
smoke plumes of burning biomass and in phytoplankton in the world's oceans. The relative warming ef-
fects of halons is 6,000 times that of carbon dioxide.
•
Hydrochlorofluorocarbons (HCFCs)
are modified CFCs, having fewer chlorine atoms and are con-
sidered less dangerous than CFCs. HCFCs tend to stay in the troposphere longer than CFCs. HCFCs are
used as replacement coolants in air conditioners and refrigerators and in foam and insulation production.
•
Hydrofluorocarbons (HFCs)
are modified CFCs, having no chlorine atoms. HFCs like HCFCs tend to
stay in the troposphere longer than CFCs—in the case of HFCs, 15 to 400 years. HFCs are used as
coolants in air conditioners and refrigerators and in production of foam and insulation. HFCs tend to be
less effective than CFCs as coolants.
•
Methane
is a naturally occurring gas with a lifespan of approximately 15 years in the troposphere and a
warming factor of 25 times that of carbon dioxide. There are many sources of methane, including the
production of rice, cattle, and coal, as well as natural gas leaks, especially during the transporting of nat-
ural gas in pipelines. Interestingly, organisms currently frozen in permafrost produce methane if thawed,
and as the tundra melts due to global warming, these organisms will begin to contribute their methane,
increasing the rate of warming.
•
Nitrous oxide (N
2
O)
can stay in the troposphere for about 115 years. Its relative warming potential is
300 times greater than carbon dioxide. The sources of nitrous oxide include the burning of fossil fuels,
livestock waste, fertilizers, and the manufacturing of plastics.
•
Sulfur hexafluoride (SF
6
)
is used largely in heavy industry to insulate high-voltage equipment and to as-
sist in the manufacture of cable cooling systems. It is used as a replacement for the highly carcinogenic
pollutant PCBs. Of the ten greenhouse gases described here, it has the longest potential time in the tro-
posphere at 3,200 years and the highest relative warming potential (24,000 times that of carbon dioxide).
•
Water vapor
concentrations fluctuate by geographic regions, but human activity does not significantly
affect water vapor concentrations except in local areas of large agricultural irrigation. Although as tem-
peratures increase on the planet, more water evaporates and can cause additional water vapor to rise into
the atmosphere. Water vapor is naturally occurring.
The
man-made greenhouse effect
is the process by which manmade, "greenhouse" gases are released into at-
mosphere, where they act like an insulating blanket, trapping heat in the troposphere that would otherwise re-
flect into space. The majority of the scientific community believes that human activities contribute to global
warming, but the topic is widely debated, partly due to the fact that many businesses produce greenhouse gases
and reducing the emission of these gases costs money. Most of the greenhouse effect takes place in the tropo-
sphere, where levels of several greenhouse gases have increased since large-scale industrialization began 150
years ago. Carbon dioxide is increasing due to the burning of fossil fuels and deforestation. Nitric oxide is in-
creasing due to the burning of fossil fuels. Part of the methane increase is due to the decomposition of organic
material in the permafrost, increased cattle production, and the melting of methyl hydrates as ocean temperat-
ures rise (scientists are searching for additional causes of increased methane). CFCs were not manufactured un-
til the 1930s so all atmospheric CFCs are human-made.
