CHEMISTRY ATMOSPHERES

INTRODUCTION

The thick blanket of air which envelopes our planet and helps sustain life is called the atmosphere. Atmosphere behaves as a protecting shield for all life on Earth, making it unique in the solar system. The atmospheric gases which are used in respiration and photosynthesis are called air.

The atmosphere of the Earth contains a mixture of gases which are forced to be maintained near the Earth's surface by gravity. An increase in altitude will decrease the density of the atmosphere. Maximum atmosphere is located close to the surface, within 16 kilometers. Though the atmosphere extends into outer space and there is no distinct border between them, an imaginary line called the Kármán Line, which is approximately at the height of 100 km, is called as the boundary of Earth's atmosphere.

The atmosphere protects life on Earth by serving the following functions:

  • absorbs the energetic ultraviolet radiation while allowing the important visible radiations to pass;

  • keep the Earth's surface warm through heat retention, making possible a comfortable mean temperature of ‡15°C;

  • prevents excessive heating of the surface of the Earth at day, and excessive cooling at night thereby reducing the temperature variations;
    contains nitrogen, oxygen and carbon dioxide gases essential for plant growth and for respiration;

  • protects the surface of the Earth and all life existing on Earth from small meteorites that heat up in the atmosphere due to friction;

  • serves as an integral part in the biogeochemical cycles of carbon, nitrogen, oxygen, phosphorus and sulfur;

  • helps in flow of energy and water vapors through dynamic processes of airflow;

  • helps in radio communication;

  • helps in movement of aircrafts;

  • aid in dissipation, dispersion and decomposition of pollutants.

There are five layers of the earth's atmosphere based on the variation in vertical temperature in each layer: troposphere, stratosphere, mesosphere, thermosphere and exosphere.

Troposphere

Troposphere is the closest layer to the Earth's surface. Thus, the layer we live in is the troposphere. It is about 18 km above the sea level at the equator, and 7 km at the poles. 75% of the atmospheric gases are present in this layer and almost all of the dust particles and water vapors. All weather phenomenon like cloud formation, winds, rainfall, snowfall takes place in this layer.

The air below this layer is warmer than any other other layer because it is heated from the Earth's surface below. The layer of air which is warm tends to rise up, and a pocket of cold air flows to cover the space, giving rise to wind movement. The temperature will decrease at a rate of about 6.5°C per kilometer as the altitude increases. The average temperature near the surface is 15°C while it is -57°C at the top. Pressure, moisture content and density of air also decrease with height thinning of air. That is why people experience breathlessness at high altitudes.