Amount of moisture in the air, indicated in kg/kg of dry air.



Related Terms

AIR-MASS CLASSIFICATION

Air masses are classified according to their source regions. Four such regions are generally recognized- (1) equatorial (E), the doldrum area between the north and south trades; (2) tropical (T), the trade wind and lower temperate regions, (3) polar (P), the higher temperate latitudes; and (4) Arctic or Antarctic (A), the north or south polar regions of ice and snow. This classification is a general indication of relative temperature, as well as latitude of origin. Air masses are further classified as maritime (m) or continental (c), depending upon whether they form over water or land. This classification is an indication of the relative moisture content of the air mass. A third classification sometimes applied to tropical and polar air masses indicates whether the air mass is warm (w) or cold (k) relative to the underlying surface. The w and k classifications are primarily indications of stability, cold air being more stable.

AIR DRYING

Removing moisture from a material by exposure to air to the extent that no further moisture is released on contact with air.

D.A.L.R.

Dry adiabatic lapse rate is approx. 9.8o C per kilometre being the temperature change of unsaturated air on rising or falling.

DEW

Moisture droplets that condense when air cools.

DRY EXHAUST

An exhaust system or part of an exhaust system that is uncooled or cooled by air currents. Dry exhaust systems operate at higher temperatures than water cooled.

HAIR HYGROMETER

A hygrometer in which the sensing element is a bundle of human hair, which is held under slight tension by a spring and which expands and contracts with changes in the moisture of the surrounding air or gas.

HAZARDOUS AIR POLLUTANTS

Chemicals that are known or suspected to cause cancer or other serious health effects, such as reproductive effects or birth defects, or adverse environmental effects. Listed hazardous air pollutants include benzene, found in gasoline; perchlorethlyene, emitted from some dry cleaning facilities; and methylene chloride, used as a solvent and paint stripper in industry; as well as dioxin, asbestos, toluene, and metals such as cadmium, mercury, harmonic vibration See harmonic motion.

POLAR AIR

A type of air whose characteristics are developed over high latitudes, especially Within the subpolar highs. Continental polar air has low surface temperature, low moisture content, and especially in its source regions, has great stability in the lower layers. It is shallow in comparison with arctic air. Maritime polar air initially possesses similar properties to those of continental polar air, but in passing over warmer water it becomes unstable with a higher moisture content.

DEW-POINT TEMPERATURE

The temperature that the air must be cooled in order for dew to form and a measure of the air's moisture content.

SLING PSYCHROMETER

Measuring device with wet and dry bulb thermometers. Moved rapidly through air it measures humidity.

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