ABSTRACT
The atmosphere is essential to life. It also serves a vital protective function to living species and one can wonder how life on earth would have evolved had the atmosphere been different in composition. The atmosphere is life-supporting by virtue of the relatively high proportion of molecular oxygen which exists in spite of the presence of gases such as nitrogen, methane, hydrogen and other gases that are capable of existing in various oxide forms. The atmosphere is the source of oxygen for respiration and carbon dioxide for photosynthesis. The atmosphere is stratified on the basis of temperature-density relationships resulting from interrelationships between physical and photochemical processes in air. Particles are common significant components of the atmosphere, particularly the troposphere. Colloidal-sized particles in the atmosphere are called aerosols. The dispersion of chemical pollutants in the atmosphere is determined by mean wind flow conditions and by atmospheric turbulence. Pollutants emitted into the atmosphere or formed in the atmosphere are eventually depleted.
