Particulate Solids suspended in water, wastewater, or air that can vary widely in
shape, size, density, and charge.
Parts per billion (ppb) Number of parts of a chemical found in one billion parts of
a particular gas, liquid, or solid mixture.
Parts per million by volume (ppmv) Number of parts of a chemical found in one
million parts of a particular gas, liquid, or solid.
Parts per trillion (ppt) Number of parts of a chemical found in one trillion parts of
a particular gas, liquid, or solid.
Pathogen It is a bacterium, virus, or other microorganism that can cause disease.
Pathogenic organisms Bacteria, viruses, or cysts, which can cause disease
(typhoid, cholera, dysentery) in a host such as a human. Also called pathogens.
Percolation The movement or flow of water through soil or rocks.
Perennial crops They are crops developed to reduce inputs necessary to produce
food by greatly reducing the need to replant crops from year to year.
Perfluorocarbons (PFCs) A group of chemicals composed of carbon and fluorine
only. These chemicals (predominantly CF4 and C2F6) were introduced as alternatives, along with hydrofluorocarbons, to the ozone-depleting substances. In
addition, PFCs are emitted as by-products of industrial processes and are also
used in manufacturing. PFCs do not harm the stratospheric ozone layer, but they
are powerful greenhouse gases: CF4 has a global warming potential (GWP) of
7390 and C2F6 has a GWP of 12,200. The GWP is from the IPCC’s Fourth
Assessment Report (AR4). These chemicals are predominantly human-made,
though there is a small natural source of CF4.
Performance Normally expressed as the amount of cooling for a given quantity of
water at a given wet bulb temperature.
Permafrost Perennially (continually) frozen ground that occurs where the temperature remains below 0
C for several years.
Pest A destructive insect or other animal that attacks crops, food, livestock, human,
or structure, etc. For instance, the tomato plant attracts a pest called whitefly, and
the wood frame house attracts a pest called termite.
Pesticide It is a substance, usually a chemical, used for destroying insects or other
organisms harmful to cultivated plants or to animals
pH (a) The negative logarithm of the hydrogen ion concentration (Àlog10[H
+
])
where H
+ is the hydrogen-ion concentration in moles per liter. Neutral water has a
pH value of 7. (b) An expression of both acidity and alkalinity on a scale of 0 to
14, with 7 representing neutrality; numbers less than 7 indicate increasing acidity
and numbers greater than 7 indicate increasing alkalinity. Acid rain can increase
the pH level of the water in a lake, thereby killing all life.
pH adjustment A means of maintaining the optimum pH through the use of
chemical additives.
Phenology The timing of natural events, such as flower blooms and animal migration, which is influenced by changes in climate. Phenology is the study of such
important seasonal events. Phenological events are influenced by a combination
of climate factors, including light, temperature, rainfall, and humidity.
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shape, size, density, and charge.
Parts per billion (ppb) Number of parts of a chemical found in one billion parts of
a particular gas, liquid, or solid mixture.
Parts per million by volume (ppmv) Number of parts of a chemical found in one
million parts of a particular gas, liquid, or solid.
Parts per trillion (ppt) Number of parts of a chemical found in one trillion parts of
a particular gas, liquid, or solid.
Pathogen It is a bacterium, virus, or other microorganism that can cause disease.
Pathogenic organisms Bacteria, viruses, or cysts, which can cause disease
(typhoid, cholera, dysentery) in a host such as a human. Also called pathogens.
Percolation The movement or flow of water through soil or rocks.
Perennial crops They are crops developed to reduce inputs necessary to produce
food by greatly reducing the need to replant crops from year to year.
Perfluorocarbons (PFCs) A group of chemicals composed of carbon and fluorine
only. These chemicals (predominantly CF4 and C2F6) were introduced as alternatives, along with hydrofluorocarbons, to the ozone-depleting substances. In
addition, PFCs are emitted as by-products of industrial processes and are also
used in manufacturing. PFCs do not harm the stratospheric ozone layer, but they
are powerful greenhouse gases: CF4 has a global warming potential (GWP) of
7390 and C2F6 has a GWP of 12,200. The GWP is from the IPCC’s Fourth
Assessment Report (AR4). These chemicals are predominantly human-made,
though there is a small natural source of CF4.
Performance Normally expressed as the amount of cooling for a given quantity of
water at a given wet bulb temperature.
Permafrost Perennially (continually) frozen ground that occurs where the temperature remains below 0
C for several years.
Pest A destructive insect or other animal that attacks crops, food, livestock, human,
or structure, etc. For instance, the tomato plant attracts a pest called whitefly, and
the wood frame house attracts a pest called termite.
Pesticide It is a substance, usually a chemical, used for destroying insects or other
organisms harmful to cultivated plants or to animals
pH (a) The negative logarithm of the hydrogen ion concentration (Àlog10[H
+
])
where H
+ is the hydrogen-ion concentration in moles per liter. Neutral water has a
pH value of 7. (b) An expression of both acidity and alkalinity on a scale of 0 to
14, with 7 representing neutrality; numbers less than 7 indicate increasing acidity
and numbers greater than 7 indicate increasing alkalinity. Acid rain can increase
the pH level of the water in a lake, thereby killing all life.
pH adjustment A means of maintaining the optimum pH through the use of
chemical additives.
Phenology The timing of natural events, such as flower blooms and animal migration, which is influenced by changes in climate. Phenology is the study of such
important seasonal events. Phenological events are influenced by a combination
of climate factors, including light, temperature, rainfall, and humidity.
12 Glossary of Natural Resources and Environmental Pollution Control
471