Absorption
Process by which a substance or particle is drawn into
the structure of another.
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ACH
See "Air Changes Per Hour."
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Acid Rain
The precipitation of dilute solutions of strong mineral
acids, formed by the mixing in the atmosphere of various industrial
pollutants (primarily sulfur dioxide and nitrogen oxides) with naturally
occurring oxygen and water vapor.
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Acute Exposure
A single exposure to a toxic substance that
may result in severe biological harm or death. Acute exposures are usually
characterized as lasting no longer than a day, as compared to longer,
continuing exposure over a period of time.
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Acute Toxicity
The ability of a substance to cause severe
biological harm or death soon after a single exposure or dose. Also,
any poisonous effect that results from a single short-term exposure
to a toxic substance.
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Adaptive Reuse
Renovation of a building or site to include
elements that allow a particular use or uses to occupy a space that
originally was intended for a different use.
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Adsorbent
Material that is capable of the binding and
collection of substances or particles on its surface without chemically
altering them.
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Aerobic Treatment
Process by which microbes decompose complex
organic compounds in the presence of oxygen and use the liberated energy
for reproduction and growth.
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Aerosol
Suspended droplets of liquid or liquid dispersions
in air.
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Air Changes Per Hour (ACH)
Number of times per hour a volume of air,
equivalent to the volume of space, enters that space.
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Air Exchange Rate
The rate at which outside air replaces indoor
air in a given space. Also see "Air Changes Per Hour."
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Air Handling Unit
Equipment that includes a fan or blower,
heating and/or cooling coils, regulator controls, condensate drain pans,
and air filters.
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Air Plenum
Any space used to convey air in a building,
furnace or structure. The space above a suspended ceiling is often used
as an air plenum.
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Air Pollutant:
Any substance in air that could, in high
enough concentration, harm man, other animals, vegetation or material.
Pollutants may include almost any natural or artificial composition
of matter capable of being airborne. They may be in the form of solid
particles, liquid droplets, gases or any combination thereof. Air pollutants
are often grouped in categories for ease in classification. Some of
these categories are solids, sulfur compounds, volatile organic chemicals,
particulate matter, nitrogen compounds, oxygen compounds, halogen compounds,
radioactive compounds and odors.
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Air Pollution
The presence of contaminants or pollutant
substances in the air that interfere with human health or welfare, or
produce other harmful environmental effects.
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Air Toxics
Any air pollutant for which a National Ambient
Air Quality Standard (NAAQS) does not exist that may reasonably be anticipated
to cause serious or irreversible chronic or acute health effects in
humans.
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Airborne Particulates
Total suspended particulate matter found
in the atmosphere as solid particles or liquid droplets. Chemical composition
of particulates varies widely, depending on location and time of year.
Sources of airborne particulates include dust, emissions from industrial
processes, combustion products from the burning of wood and coal, combustion
products associated with motor vehicle or non-road engine exhausts,
and reactions to gases in the atmosphere.
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Alternative Energy
Energy from a source other than the conventional
fossil-fuel sources of oil, natural gas and coal (i.e., wind, running
water, the sun). Also referred to as "alternative fuel."
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Ambient Air
The surrounding air.
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Antimicrobial
An agent that kills microbes.
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ASHRAE
American Society of Heating, Refrigeration
and Air Conditioning Engineers.
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