Air carrierAn operator (e.g., airline) in the commercial system of air transportation consisting of aircraft that hold certificates of, Public Convenience and…
Air ChangeA measure of the rate at which the air in an interior space is replace by outside (or conditioned) air by ventilation and infiltration; usually measured…
Air CollectorIn solar heating systems, a type of solar collector in which air is heated in the collector.
Air ConditionerA device for conditioning air in an interior space. A Room Air Conditioner is a unit designed for installation in the wall or window of a room to deliver…
Air ConditioningThe control of the quality, quantity, and temperature-humidity of the air in an interior space.
air densityThe mass per unit volume of air; about 1.275 kilometer per cubic meter at 0° C and 1000 millibars.
Air DiffuserAn air distribution outlet, typically located in the ceiling, which mixes conditioned air with room air.
Air Infiltration MeasurementA building energy auditing technique used to determine and/or locate air leaks in a building shell or envelope.
Air MassA body of air covering a relatively wide area and exhibiting horizontally uniform properties.
Air Mass ThunderstormGenerally, a thunderstorm not associated with a front or other type of synoptic-scale forcing mechanism.
Air pollutantAny substance in the air which could, if in high enough concentration, harm humans, other animals, vegetation, or material.
Air PollutionThe presence of contaminants in the air in concentrations that prevent the normal dispersive ability of the air, and that interfere with biological…
Air Pollution ControlThe use of devices to limit or prevent the release of pollution into the atmosphere.
Air Pollution PotentialThe meteorological potential for air pollution problems, considered without regard to the presence or absence of actual pollution sources.
Air PressureSpecifically the air pressure of the tires. Changing the air pressure in the tires is a way to alter the setup and handling of a NASCAR race car.
Air qualityMeasure of the health-related and visual characteristics of the air to which the general public and the environment are exposed.
Air Quality Control Region (AQCR)An interstate or intrastate area designated by the U.S. Environmental Protection Agency for the attainment and maintenance of National Ambient Air Quality…
Air Quality ModelMathematical or conceptual model used to estimate present or future air quality.
Air Quality StandardsThe prescribed level of pollutants allowed in outside or indoor air as established by legislation.
Air RegisterThe component of a combustion device that regulates the amount of air entering the combustion chamber.
Air release valveA valve, usually manually operated, which is used to release air from a pipe or fitting.
Air Retarder/BarrierA material or structural element that inhibits air flow into and out of a building's envelope or shell.
Air slakingThe process of breaking up or sloughing when an indurated soil is exposed to air.
Air SpaceThe area between the layers of glazing (panes) of a window.
Air StagnationA meteorological situation in which there is a major buildup of air pollution in the atmosphere.
Air Stagnation AdvisoryThis National Weather Service product is issued when major buildups of air pollution, smoke, dust, or industrial gases are expected near the ground for a…
Air temperatureAir temperature (Also termed surface temperature in meteorology). The ambient temperature indicated by a thermometer exposed to the air but sheltered from…
Air Transportable Mobile UnitA modularized transportable unit containing communications and observational equipment necessary to support a meteorologist preparing on-site forecasts at…
Air VentA pipe designed to provide air to the outlet conduit to reduce turbulence and prevent negative pressures during release of water.
Air wavesAir borne vibrations caused by explosions.
Air-Source Heat PumpA type of heat pump that transfers heat from outdoor air to indoor air during the heating season, and works in reverse during the cooling season.
Air-space ratioRatio of volume of water that can be drained from a saturated soil or rock under the action of force of gravity to total volume of voids.
Air-to-Water Heat PumpA type of heat pump that transfers heat in outdoor air to water for space or water heating.
Air-void ratioThe ratio of the volume of airspace to the total volume of voids in a soil mass.
Airborne Snow Survey ProgramCenter (NOHRSC) program that makes airborne snow water equivalent and soil moisture measurements over large areas of the country that are subject to…
Airborne Snow Water Equivalent Measurement TheoryA theory based on the fact that natural terrestrial gamma radiation is emitted from the potassium, uranium, and thorium radioisotopes in the upper eight…
airlift fermenterA cylindrical fermentation vessel in which the cells are mixed by air introduced at the base of the vessel and that rises through the column of culture…
Airlock EntryA building architectural element (vestibule) with two airtight doors that reduces the amount of air infiltration and exfiltration when the exterior most…
Airtight Drywall Approach (ADA)A building construction technique used to create a continuous air retarder that uses the drywall, gaskets, and caulking.
Alagille syndromeA rare inherited liver disorder seen in infants and young children. The disease is characterized by a buildup of bile in the liver due to a deficiency or…
Alaska CurrentA North Pacific Ocean current flowing counterclockwise in the Gulf of Alaska. It is the northward flowing (warm) division of the Aleutian Current
AlbedoThe ratio of light reflected by a surface to the light falling on it.
Albedo (effects)The fraction of solar radiation reflected by a surface or object, often expressed as a percentage.
Alberta ClipperA fast moving low pressure system that moves southeast out of Canadian Province of Alberta (southwest Canada) through the Plains, Midwest, and Great Lakes…
Alberta LowAlberta Low A low centered on the eastern slope of the Canadian Rockies in the province of Alberta, Canada.
albinism(AL-bye-niz-em) A group of genetic conditions marked by little or none of the pigment melanin in the skin, hair, and/or eyes.
albino1. An organism lacking pigmentation, due to genetic factors. The condition is albinism 2. A conspicuous plastid mutant involving loss of chlorophyll.
ALCAgency Location Code - an eight (8) digit code assigned to U.S. government agencies by the Department of Treasury.
alcohol(AL-kuh-hol) A chemical substance found in beer, wine, and liquor. Alcohol is also found in some medicines, mouthwashes, essential oils (scented liquid…
aldehyde(AL-deh-hide) A type of chemical substance made from alcohol. Aldehydes are found in essential oils (scented liquid taken from plants).
aldosesOccur when the carbonyl group of a monosaccharide is an aldehyde. (Source: Voet, D.; Voet, J. G. Biochemistry. New York: John Wiley, 1990.)
ALERTAutomated Local Event Reporting in Real Time. Network of automatic raingauges that transmit via VHF radio link when precipitation occurs.
Alert (Automated Local Evaluation in Real Time)A flood warning system consisting of remote sensors, data transmission by radio, and a computer software package developed by the National Weather Service…
ALERT Flood Warning SystemA cooperative, community-operated flood warning system; the acronym stands for Automated Local Evaluation (in) Real Time.
Alert StageThe elevation, or stage, of a stream at which need-to-know officials (e.g., county sheriff, civil defense officials, bypass gate operators) are notified…
aleuroneThe outermost layer of the endosperm in a seed, and the site of enzymes concerned with endosperm digestion during seedling growth.
Aleutian CurrentAn eastward flowing North Pacific Ocean current which lies north of the North Pacific Current.
Aleutian LowA semi-permanent, subpolar area of low pressure located in the Gulf of Alaska near the Aleutian Islands.
AlevinA young fish which has not yet absorbed its yolk sac.
AlgaeSimple plant organism (typically a single cell) commonly found in water.
Algae bloomA heavy growth of algae in and on a body of water as a result of high phosphate concentration from farm fertilizers and detergents.
algal biomassSingle-celled plants (e.g. Chlorella spp. and Spirulina spp.) grown commercially in ponds to make feed materials for zooplankton, which are in turn…
Algal bloomRapid and flourishing growth of algae. Sudden, massive growths of microscopic and macroscopic plant life, such as green or bluegreen algae, which develop…
AlgicideAny substance or chemical specifically formulated to kill or control algae.
AlgorithmA detailed formula or set of steps for solving a particular problem. To be an algorithm, a set of rules must be unambiguous and have a clear stopping…
ALIASINGWhen computer graphics output has jagged edges or a stair-stepped, rather than a smooth, appearance when magnified.
Aliquot (parts)The standard subdivisions of a section (usually 640 acres [2.6 km2]) of land, such as a half section, quarter section, or quarter-quarter section.
alkali ligninLignin obtained by acidification of an alkaline extract of wood.
Alkali sinkA land basin in which water evaporation produces high salt concentrations that may, or may not, support salt marsh vegetation.
Alkali-aggregate reaction (AAR)A deterioration of concrete by which the alkali in the cement paste in the concrete reacts chemically with the silica or carbonate present in some…
Alkali-carbonate reaction (ACR)Reaction of alkalis which occurs between certain argillaceous dolomitic limestones and the alkaline pore solution in the concrete and causes expansion and…
Alkali-silica reaction (ASR)Reaction of alkalis with aggregate with various forms of poorly crystalline reactive silica: opal, chert, flint and chalcedony and also tridymite…
Alkali-silicate/silica reaction (ASSR)Reaction of alkalis with strained quartz is thought to be one reactive component of aggregates causing this reaction.
AlkalineHaving a pH of 7.0 or above. The condition of water or soil which contains a sufficient amount of alkali substances to raise the pH above 7.0.
alkaline hydrolysisThe use of solutions of sodium hydroxide (or other alkali) in the treatment of cellulosic material (wood) to break down cellulose to simple sugars.
AlkalinityThe total concentration of bases in water.
alkylating agent(AL-kuh-LAY-ting AY-jent) A type of drug that is used in the treatment of cancer. It interferes with the cell's DNA and inhibits cancer cell growth.
All-American CanalThe All-American Canal System, located in the southeastern corner of California, consists of the Imperial Diversion Dam and Desilting Works, the…
All-American RoadsA National Scenic Byway is a road recognized by the U.S. Department of Transportation for its archeological, cultural, historic, natural, recreational…
alleleA variant form of a gene. In a diploid cell there are two alleles of every gene (one inherited from each parent, although they could be identical).
allele frequencyThe relative number of copies of an allele in a population, expressed as a proportion of the total number of copies of all alleles at a given locus in a…
allele-specific amplification(Abbreviation: ASA). The use of the polymerase chain reaction at a sufficiently high stringency that only one allele is amplified.
AllelesAlternate forms of a gene or DNA sequence, which occur on either of two homologous chromosomes in a diploid organism. (See DNA polymorphism.)