Hydrochlorofluorocarbons (HCFCs) Compounds containing hydrogen, fluorine,
chlorine, and carbon atoms. Although ozone-depleting substances, they are less
potent at destroying stratospheric ozone than chlorofluorocarbons (CFCs). They
have been introduced as temporary replacements for CFCs and are also greenhouse gases.
Hydrofluorocarbons (HFCs) Compounds containing only hydrogen, fluorine, and
carbon atoms. They were introduced as alternatives to ozone-depleting substances in serving many industrial, commercial, and personal needs. HFCs are
emitted as by-products of industrial processes and are also used in manufacturing.
They do not significantly deplete the stratospheric ozone layer, but they are
powerful greenhouse gases with global warming potentials ranging from
140 (HFC-152a) to 11,700 (HFC-23).
Hydrogen sulfide gas (H 2 S) A gas with a rotten egg odor. This gas is produced
under anaerobic conditions. Hydrogen sulfide is particularly dangerous because it
dulls the sense of smell so that it is unnoticeable after a prolonged period of time
and because the odor is not noticeable in high concentrations. The gas is colorless, explosive, flammable, and poisonous to the respiratory system.
Hydrologic cycle The process of evaporation, vertical and horizontal transport of
vapor, condensation, precipitation, and the flow of water from continents to
oceans. It is a major factor in determining climate through its influence on surface
vegetation, the clouds, snow and ice, and soil moisture. The hydrologic cycle is
responsible for 25 to 30 percent of the mid-latitudes’ heat transport from the
equatorial to polar regions.
Hydrology It is a branch of science concerned with the properties of the Earth’s
water, and especially its movement in relation to land.
Hydrosphere The component of the climate system comprising liquid surface and
subterranean water, such as: oceans, seas, rivers, fresh water lakes, underground
water etc.
Hypochlorination Application of sodium hypochlorite (liquid) for disinfection is
also called hypochlorination. It achieves the same result as that of chlorination
using chlorine gas. Its use is generally limited to smaller water or wastewater
treatment facilities or where there are significant health and safety concerns
regarding the handling and use of chlorine gas.
Ice core A cylindrical section of ice removed from a glacier or an ice sheet in order
to study climate patterns of the past. By performing chemical analyses on the air
trapped in the ice, scientists can estimate the percentage of carbon dioxide and
other trace gases in the atmosphere at a given time. Analysis of the ice itself can
give some indication of historic temperatures.
Ignitability Any substance that exhibits any of the following properties is considered a hazardous substance due to ignitability: (a) a liquid that has a flash point
less than 60
C; (b) a nonliquid capable, under normal conditions, of spontaneous
and sustained combustion; (c) an ignitable compressed gas under the US Department of Transportation (DOT) regulations; and (d) an oxidizer under DOT
regulations.
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457
chlorine, and carbon atoms. Although ozone-depleting substances, they are less
potent at destroying stratospheric ozone than chlorofluorocarbons (CFCs). They
have been introduced as temporary replacements for CFCs and are also greenhouse gases.
Hydrofluorocarbons (HFCs) Compounds containing only hydrogen, fluorine, and
carbon atoms. They were introduced as alternatives to ozone-depleting substances in serving many industrial, commercial, and personal needs. HFCs are
emitted as by-products of industrial processes and are also used in manufacturing.
They do not significantly deplete the stratospheric ozone layer, but they are
powerful greenhouse gases with global warming potentials ranging from
140 (HFC-152a) to 11,700 (HFC-23).
Hydrogen sulfide gas (H 2 S) A gas with a rotten egg odor. This gas is produced
under anaerobic conditions. Hydrogen sulfide is particularly dangerous because it
dulls the sense of smell so that it is unnoticeable after a prolonged period of time
and because the odor is not noticeable in high concentrations. The gas is colorless, explosive, flammable, and poisonous to the respiratory system.
Hydrologic cycle The process of evaporation, vertical and horizontal transport of
vapor, condensation, precipitation, and the flow of water from continents to
oceans. It is a major factor in determining climate through its influence on surface
vegetation, the clouds, snow and ice, and soil moisture. The hydrologic cycle is
responsible for 25 to 30 percent of the mid-latitudes’ heat transport from the
equatorial to polar regions.
Hydrology It is a branch of science concerned with the properties of the Earth’s
water, and especially its movement in relation to land.
Hydrosphere The component of the climate system comprising liquid surface and
subterranean water, such as: oceans, seas, rivers, fresh water lakes, underground
water etc.
Hypochlorination Application of sodium hypochlorite (liquid) for disinfection is
also called hypochlorination. It achieves the same result as that of chlorination
using chlorine gas. Its use is generally limited to smaller water or wastewater
treatment facilities or where there are significant health and safety concerns
regarding the handling and use of chlorine gas.
Ice core A cylindrical section of ice removed from a glacier or an ice sheet in order
to study climate patterns of the past. By performing chemical analyses on the air
trapped in the ice, scientists can estimate the percentage of carbon dioxide and
other trace gases in the atmosphere at a given time. Analysis of the ice itself can
give some indication of historic temperatures.
Ignitability Any substance that exhibits any of the following properties is considered a hazardous substance due to ignitability: (a) a liquid that has a flash point
less than 60
C; (b) a nonliquid capable, under normal conditions, of spontaneous
and sustained combustion; (c) an ignitable compressed gas under the US Department of Transportation (DOT) regulations; and (d) an oxidizer under DOT
regulations.
12 Glossary of Natural Resources and Environmental Pollution Control
457