| Section A | A index | 321-329 of 917 terms |
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air sampler—A device used on a moving platform such as an aircraft that, when quickly opened and closed, captures a representative sample of the atmosphere.
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air–sea interaction—The processes that occur as a consequence of the air being in contact with the sea surface, and that affect the dynamics and thermodynamics of the air and water boundary layers. These include 1) the exchange of momentum, heat, mechanical energy (e.g., wave energy, turbulence), and mass (water vapor, gas species, particulates, sea spray, air bubbles, etc.); 2) the generation of surface waves; 3) the generation of turbulence; and 4) the resulting effects on the vertical profiles of wind and current.
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air toxins—Hazardous air pollutants that are known or suspected to cause cancer or other serious health effects (such as birth or developmental defects). The U.S. Clean Air Act Amendments of 1990 require emission reductions for 188 hazardous air pollutants from industrial factories and other sources. As of 1996, the U.S. Environmental Protection Agency has issued standards for 47 source categories, such as chemical plants, oil refineries, aerospace manufacturers, and steel mills, as well as dry cleaners, commercial sterilizers, secondary lead smelters, and chromium electroplating processors. Compare designated pollutant, criteria pollutants; see downwash.
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air trap—A device incorporated in some types of mercury barometer to prevent air or other gaseous impurities from entering into the vacuum space.
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air—Mixture of gases forming the earth's atmosphere, consisting of nitrogen (∼78 percent), oxygen (∼21 percent), water vapor, and other trace gases such as carbon dioxide, helium, argon, ozone, or various pollutants. The concentration of water vapor is very variable, being a strong function of temperature and, hence, altitude in the atmosphere. Dry air is referred to as air from which measurable amounts of water vapor have been physically removed. Pure, dry air has a density of 1.293 kg m−3 at a temperature of 273 K and a pressure of 101.325 kPa. Apart from the variability of water vapor, the composition of air is essentially constant to an altitude of at least 50 km and is presently approximated as follows. The concentration of ozone is variable, between 10 and 0.1 parts per million. Carbon dioxide, methane, and nitrous oxide have all been increasing since the beginning of the industrial age.
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airborne expendable bathythermograph—(Abbreviated AXBT.) An expendable instrument that is dropped from an aircraft and used to measure the profile of temperature in the water column. The probe consists of a thermistor in a weighted, streamlined case. It falls freely at a fixed, known rate so that the elapsed time can be converted to depth. It is connected by a thin, freely unwinding wire to a small buoy with a radio transmitter through which the data are transmitted to the aircraft, which continues its flight.
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