Chapter 8. Composition and Structure of Atmosphere

• Air is essential for survival of all organisms. Some organisms like humans may survive for some time without food and water but can’t survive even a few minutes without breathing air.
• air is an integral part of earth’s mass and 99% of total mass of atmosphere is confined to height of 32 km from earth’s surface.

Composition of Atmosphere
• atmosphere is composed of gases, water vapour and dust particles.
• proportion of gases changes in higher layers of atmosphere in such a way that oxygen is almost in negligible quantity at height of 120 km.

• Carbon dioxide is meteorologically a very important gas as it is transparent to incoming solar radiation but opaque to outgoing terrestrial radiation.
• volume of other gases is constant but volume of carbon dioxide has been rising in past few decades mainly because of burning of fossil fuels.

Dust Particles
• atmosphere has enough space to hold small solid particles. These particles can come from many different places, such as sea salts, fine soil, smoke-soot, ash, pollen, dust, and pieces of meteors that have broken apart.
• Because of dry winds, there are more dust particles in subtropical and temperate regions than in equatorial and polar regions.

Water Vapour
• Water vapour is a variable gas in atmosphere, which decreases with altitude.
• In warm and wet tropics, it may account for four percent of air by volume, while in dry and cold areas of desert and polar regions it may be less than 1%.

Structure of Atmosphere
• atmosphere consists of different layers with varying densities and temperatures.
• troposphere is lowermost layer of atmosphere.
• zone separating troposphere from stratosphere is called tropopause.

Elements of Weather and Climate
• main elements of atmosphere which are subject to change and which influence human life on earth are temperature, pressure, winds, humidity, clouds & precipitation.

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