Environmental Engineering Reference
In-Depth Information
gas hydrate deposits as a result of extraction activities or climate
change. Recent research revealed that there are more than 250 plumes
of methane gas bubbles rising from an area of seabed in the Arctic,
which scientists believe are being released from methane hydrates that
become unstable as the Arctic Ocean warms. 49 For marine gas hydrates,
some of the released methane would probably be oxidized in the sedi-
ments and water column; some might dissolve in the ocean; and some
might reach the atmosphere either immediately or over time. For per-
mafrost gas hydrates, the potential for direct outgassing of methane
to the atmosphere is considerably greater.
Other Gases
Small contributions to global warming are made by several other gases,
but they are present in only tiny amounts in the atmosphere and are not
a major source of concern. Nitrous oxide increases are due mostly to the
increased use of fertilizers. It has an atmospheric lifetime of 114 years.
Chlorofl uorocarbons, refrigerant fl uids used in refrigerators and air con-
ditioners, are destroyed in the atmosphere at about the same rate as
methane. CFCs are being phased out by manufacturers.
Solid Particles
Two types of particles in the atmosphere affect global warming: sulfate
aerosols and soot. Sulfate aerosols arise from the burning of sulfurous
coal and oil, and they have had a measurable effect on reducing the
enhanced greenhouse effect produced by greenhouse gases because they
refl ect some of the incoming sunlight. The decrease in enhanced green-
house warming caused by aerosol emissions is a rare example of a ben-
efi cial effect of fossil fuel use. Unfortunately, the effect of the sulfate
aerosols is too small to completely counteract the effect of all the green-
house gases we have pumped into the atmosphere. Pollution controls are
reducing the amount of sulfur emitted from coal- and oil-burning indus-
tries and cars, a benefi t to our lungs (chapter 10), but as the amount of
anthropogenic sulfur in the atmosphere decreases, the rate of global
warming will increase.
Because of our burning of biomass, coal, and fuel in motor vehicles,
the United States is a major producer of black soot. In developed coun-
tries, most of it comes from the incomplete combustion of diesel fuel. In
less developed countries biomass burning is most signifi cant (table 9.5).
Once in the air, it is spread around the world by winds. In the Northern
Hemisphere, including the Arctic, soot is twice as potent as carbon
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