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ATMOSPHERE – 01

COMPOSITION OF THE ATMOSPHERE

Introduction: Earth is the only planet in the solar system with an atmosphere that can sustain life. The blanket of gases not only contains the air that we breathe but also protects us from the blasts of heat and radiation emanating from the sun. It warms the planet by day and cools it at night. Earth’s atmosphere is about 300 miles (480 kilometers) thick, but most of it is within 10 miles (16 km) the surface. Air pressure decreases with altitude. At sea level, air pressure is about 14.7 pounds per square inch (1 kilogram per square centimeter). At 10,000 feet (3 km), the air pressure is 10 pounds per square inch (0.7 kg per square cm). There is also less oxygen to breathe.

COMPOSITION OF AIR

The gases in Earth’s atmosphere include:
  • Nitrogen — 78 percent
  • Oxygen — 21 percent
  • Argon — 0.93 percent
  • Carbon dioxide — 0.04 percent
  • Trace amounts of neon, helium, methane, krypton and hydrogen, as well as water vapor
The atmosphere is composed of gases, water vapour and dust particles. The proportion of gases changes in the higher layers of the atmosphere in such a way that oxygen will be almost in negligible quantity at the height of 120 km.  Similarly, carbon dioxide and water vapour are found only up to 90 km from the surface of the earth. Nitrogen and oxygen are two gases which make up the bulk of the atmosphere. Carbon dioxide, helium, ozone, argon and hydrogen are found in lesser quantities. Nitrogen is the most plentiful gas in the air. When we inhale, we take some amount of nitrogen into our lungs and exhale it. But plants need nitrogen for their survival. They can not take nitrogen directly from the air. Bacteria, that live in the soil and roots of some plants, take nitrogen from the air and change its form so that plants can use it

CARBON DIOXIDE is another important gas. Green plants use carbon dioxide to make their food and release oxygen. Humans or animals release carbon dioxide . CARBON DIOXIDE is meteorologically a very important gas as it is transparent to the incoming solar radiation but opaque to the outgoing terrestrial radiation. It absorbs a part of terrestrial radiation and reflects back some part of it towards the earth’s surface. It is largely responsible for the green house effect.  OZONE is another important component of the atmosphere found between 10 and 50 km above the earth’s surface and acts as a filter and absorbs the ultra-violet rays radiating from the sun and prevents them from reaching the surface of the earth. OXYGEN is the second most plentiful gas in the air. Humans and animals take oxygen from the air as they breathe. Green plants produce oxygen during photosynthesis. In this way oxygen content in the air remains constant. WATER VAPOUR  Water vapour is also a variable gas in the atmosphere, which decreases with altitude. In the warm and wet tropics, it may account for four per cent of the air by volume. while in the dry and cold areas of desert and polar regions, it may be less than one per cent of the air.  Water vapour also decreases from the equator towards the poles. It also absorbs parts of the insolation from the sun and preserves the earth’s radiated heat. It thus, acts like a blanket allowing the earth neither to become too cold nor too hot.  Water vapour also contributes to the stability and instability in the air.

DUST PARTICLES 

which may originate from different sources and include sea salts, fine soil, smoke-soot, ash, pollen, dust and disintegrated particles of meteors.  Dust particles are generally concentrated in the lower layers of the atmosphere; The higher concentration of dust particles is found in subtropical and temperate regions due to dry winds in comparison to equatorial and polar regions.Dust and salt particles act as  hygroscopic nuclei around which water vapour condenses to produce clouds.

STRUCTURE OF THE ATMOSPHERE

The atmosphere consists of different layers with varying density and temperature. Density is highest near the surface of the earth and decreases with increasing altitude Our atmosphere is divided into five layers starting from the earth’s surface. These are Troposphere, Stratosphere, Mesosphere, Thermosphere and Exosphere.

TROPOSPHERE

The word troposphere is derived from the Greek tropos (meaning “turn, turn toward, change”) and sphere (as in the Earth), reflecting the fact that rotational turbulent mixing plays an important role in the troposphere’s structure and behavior. Most of the phenomena associated with day-to-day weather occur in the troposphere The troposphere is the lowest layer of atmosphere of the Earth and the layers to which changes can greatly influence the floral and faunal environments. Atmosphere of the Earth: it extends from Earth’s surface to an average height of approximately 12 km although this altitude actually varies from approximately 30,000 ft at the polar regions to 56,000 ft) at the equator, with some variation due to weather. The troposphere is bounded above by the tropopause, a boundary marked in most places by a temperature inversion (i.e., a layer of relatively warm air above a colder one), and in others by a zone which is isothermal with height. Although variations do occur, the temperature usually declines with increasing altitude in the troposphere because the troposphere is mostly heated through energy transfer from the surface. Thus, the lowest part of the troposphere (i.e., Earth’s surface) is typically the warmest section of the troposphere, which promotes vertical mixing. The troposphere contains approximately 80% of the mass of the atmosphere of the Earth. The troposphere is denser than all its overlying atmospheric layers because a larger atmospheric weight sits on top of the troposphere and causes it to be most severely compressed. Fifty percent of the total mass of the atmosphere is located in the lower 18,000 ft of the troposphere. Nearly all atmospheric water vapor or moisture is found in the troposphere, so it is the layer where most of Earth’s weather takes place. It has basically all the weather-associated cloud genus types generated by active wind circulation although very tall cumulonimbus thunder clouds can penetrate the tropopause from below and rise into the lower part of the stratosphere. Most conventional aviation activity takes place in the troposphere, and it is the only layer that can be accessed by propeller-driven aircraft.This layer is the most important layer of the atmosphere. Its average height is 13 km. The air we breathe exists here. 
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