Environmental Chemistry: Atmosphere, its composition and layers

Environmental Chemistry ⚗️

Atmosphere: The envelope of gases and water vapors surrounding our earth 🌎 is called atmosphere.

Composition of Atmosphere:

Air is a mixture of gases which are given below.

Nitrogen = 78%

Oxygen = 21%

Other gases % by volume

Argon 0.93

Carbon dioxide 0.038

Neon 0.0018

Helium 0.000052

Methane 0.00015

Krypton 0.00011

Hydrogen 0.00005

Question: Why water vapors have not been included in composition of Atmosphere?

Answer.

Besides gases, there are varying amounts of water vapors in the air. For example, there is little water in the air over the desert 🏜. Whereas in the tropical rain forest area the air may contain upto 4% water vapors. This means that amount of vapors in air varies from place to place and time to time. Therefore content of water vapors has not been included in atmospheric composition.

Layers of Atmosphere

Atmosphere is the envelop of gases and water which surrounds the earth. On the basis of temperature, atmosphere can be divided into four layers: troposphere, stratosphere, mesosphere and thermosphere. Thermosphere can be further divided into ionosphere and exosphere.

The troposphere:

The layer of atmosphere that is closest to the earth is known as troposphere. Troposphere (tropos means varying) has most variable conditions than any other layer.

Its temperature decreased from 17 oC to -55 0C.

Its temperature decrease to 6.5 oC for every 1 km increase in altitude.

It has height of 12 Km from earth’s surface.

It has the most of mass of the atmosphere (75-80 %).

It has all kinds of lives.

It has dust particles, water vapors and most of clouds.

It is the region in which aircrafts fly.

The stratosphere: The layer of atmosphere that is above the troposphere is known as troposphere.

Stratosphere (strato means spread out) has 24% of total atmosphere.

Its temperature increases from -55 °C to -5 °C.

Its height is about 38 Km from top of troposphere or 50 km from earth’s surface.

It has little water vapors. It has the maximum amount of ozone (10 ppm).

Presence of ozone protects living things from harmful effects of ultraviolet radiations coming directly from sun.

Presence of ozone is responsible for increase in temperature in stratosphere.

The mesosphere:

The layer of atmosphere that is between stratosphere and thermosphere is known as troposphere.

Mesosphere (meso means middle) is the middle layer of atmosphere.

Its temperature decrease from -5 °C to -93 °C.

Its height is about 30 km from top of s or 80 km from earth’s surface.

This layer protects earth from meteoroids.

The thermosphere:

The layer of atmosphere that is above the mesosphere is called as thermosphere.

Thermosphere has (thermo means heat) very high temperature up to 1800 °C as sunlight strikes first it.

Its height begins at 80 km above earth’s surface to outward.

This layer is divided into two layers: lower layer and outer layer.

The lower layer is ionosphere that extends 80 km to 400 km from earth surface.

Outer layer is exosphere that extends from 400 km to thousands of km from earth surface.

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