Tiny suspended particles in the atmosphere ranging in size from one nano meter to several micrometer are known as atmospheric aerosols. The sources and sinks of atmospheric aerosols are so varied and distributed over the globe that their physical and optical effects show distinct variation with geographic locations. Study of the optical and physical properties of aerosols thus become important for the assessment of their effect on climate. Because of the variability in aerosol properties, it is difficult to assess aerosol climatology. For a full assessment of aerosol characteristics, measurements have to be performed frequently in locations with different aerosol types and in varying meteorological conditions.Based on the size, aerosols are broadly classified by Junge as, (i) Aitken particles with radii less than 0.1 micro meter (ii) Large particles with radii in the range 0.1 to 1.0 micro meter and (iii) Giant particles with radii larger than 1.0 micro meter.