The atmosphere is composed of three major constituents namely gases, water vapour and gases

(a)   Gases

The gaseous composition of the atmosphere consists of two categories of gases i.e. constant or permanent gases and variable gases. These gases are nitrogen, oxygen, minor gases like carbon dioxide, ozone hydrogen, helium and methane.

(b)  Water vapour

The process of evaporation is responsible for the transformation of water into vapour. There is much temporal variation in water vapour content in the atmosphere. The content of water vapour ranges horizontally from 0.02% in the cold dry air over polar areas to 5% over moist tropical areas. The content of water vapour decreases with altitude in the atmosphere.it is also the primary greenhouse gas. More than 90% of the total atmospheric vapour is found up to a height of 5km. the moisture content in the atmosphere creates several forms of condensation and precipitation e.g. Clouds, fogs. Dew, rainfall, frost, snowfall.

(c)   Aerosols

Suspended particulate matter in the atmosphere including solid particles of varying sizes and liquid droplets are collectively called aerosols. These include dust particles from volcanic eruptions ploughed soil cover, rocks, salts particles from seas and oceans; meteoric particles; organic matter, smoke and soot. The concentration of particulate matter decreases with increasing altitude. These particulates help in selective scattering of shortwave electro-magnetic solar radiation which adds varied charming colour of red and oranges at sunrise and sunset. Some of the aerosol, mainly water droplets, absorb certain amounts of solar radiation while some amount of radiant solar energy is reflected back to space. Solid particulate matter mainly salts particles become hygroscopic nuclei and thus help in the formation of water drops. Fog, clouds, and varied forms of condensation and precipitation 

References

1.      Manahan, Stanley E. "FRONTMATTER" Environmental Chemistry, Boca Raton: CRC Press LLC, 2000

2.      FHSST Authors, The Free High School Science Texts: Textbooks for High School Students Studying the Sciences Chemistry Grades 10 – 12, Version 0, November 9, 2008