A

Air pressure

The cumulative force exerted on any surface by the molecules composing air.

Ambient temperature

Temperature of the surrounding (ambient) air.

Anemometer

An instrument designed to measure wind speed.

Aneroid barometer

An instrument designed to measure atmospheric pressure. It contains no liquid.

B

Barometer

An instrument that measures atmospheric pressure. The two most common barometers are the mercury barometer and the aneroid barometer.

Beaufort Scale

A scale for classifying the force of the wind, ranging from 0 (calm) to 12 (hurricane). A wind classified as 0 has a velocity of less than 1.6 km (1 mi) per hour; a wind classified as 12 has a velocity of over 119 km (74 mi) per hour. Other categories include light air, five levels of breeze, four levels of gale, and storm. The scale was devised in 1805 as a means of describing the effect of different wind velocities on ships at sea. It is named after an admiral in the British Navy, Sir Francis Beaufort (1774-1857).

C

Cloud base

The lowest portion of a cloud.

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M

Moon.

The natural satellite of Earth, visible by reflection of sunlight and traveling around Earth in a slightly elliptical orbit at an average distance of about 381,600 km (237,000 mi). The Moon's average diameter is 3,480 km (2,160 mi), and its mass is about 1/80 that of Earth.

N

Nitrogen Oxides (NOx)

When fossil fuels like oil, coal and natural gas are burned a mixture of oxides of nitrogen, primarily nitric oxide (NO) and nitrogen dioxide (NO2), collectively termed NOx are released into the atmosphere. Nitrogen oxides like nitric oxide (NO) and nitrogen dioxide (NO2) can react in the air to produce ozone and other harmful pollutants that lead to smog. Nitrogen dioxide emissions can also be further oxidised in air to acid gases, which contribute to the production of acid rain

Nitric oxide (NO)

Is the most common form of nitrogen directly emitted into the atmosphere. In ambient outdoor air, nitric oxide (NO), which is emitted by motor vehicles, combines with oxygen in the atmosphere under the action of sunlight, producing nitrogen dioxide (NO2) -a major air pollutant- and other NOx.

O

Ozone (O3)

Ozone is a form of oxygen having the molecular form of O3. It is a bluish, unstable gas with a pungent odour, found in two parts of the atmosphere: the stratosphere and the troposphere.

The ozone layer: The stratosphere contains a layer in which the concentration of ozone is greatest, the so called ozone layer. The layer extends from about 12 to 40 km. It shields the Earth from ultraviolet radiation's harmful health effects on humans and the environment. This layer is being depleted by human emissions of chlorine- and bromine-containing compounds.

Ground-level ozone: At ground level (in the troposphere), ozone is considered an air pollutant that can seriously affect the human respiratory system. It is a chemical oxidant and a major component of photochemical smog.

P

Prevailing wind

The wind direction most frequently observed during a given period.

PM10

Particulate matter, especially very fine particles (smaller than 10 microns – known as PM10), is thought to have a very large impact on human health and is one of the major problems facing environmental professionals. PM10 particles and even smaller fractions (PM2.5) can reach deep into our lungs and can cause severe respiratory problems as well as possibly contributing to many other conditions and diseases.

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R

Rain

Water that condenses from water vapor in the atmosphere and falls to Earth as separate drops from clouds. Rain forms primarily in three ways: at weather fronts, when the water vapor in the warmer mass of air cools and condenses; along mountain ranges, when a warm mass of air is forced to rise over a mountain and its water vapor cools and condenses; and by convection in hot climates, when the water vapor in suddenly rising masses of warm air cools and condenses.

Relative humidity

The ratio of the amount of water vapor actually in the air compared to the amount of water vapor the air can hold at the particular temperature and pressure. The ratio of the air's actual vapor pressure to its saturation vapor pressure.

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W

Weather

The state of the atmosphere in terms of such variables as temperature, cloudiness, precipitation, and radiation.

Wind

A current of air, especially a natural one that moves along or parallel to the ground, moving from an area of high pressure to an area of low pressure. Surface wind is measured by anemometers or its effect on objects, such as trees. The large-scale pattern of winds on Earth is governed primarily by differences in the net solar radiation received at the Earth's surface, but it is also influenced by the Earth's rotation, by the distribution of continents and oceans, by ocean currents, and by topography. On a local scale, the differences in rate of heating and cooling of land versus bodies of water greatly affect wind formation. Prevailing global winds are classified into three major belts in the Northern Hemisphere and three corresponding belts in the Southern Hemisphere. The trade winds blow generally east to west toward a low-pressure zone at the equator throughout the region from 30° north to 30° south of the equator. The westerlies blow from west to east in the temperate mid-latitude regions (from 30° to 60° north and south of the equator), and the polar easterlies blow from east to west out of high-pressure areas in the polar regions

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