Troposphere : The troposphere is the lowermost layer of the atmosphere . Its average height is 13 kms and extends roughly to a height of 8 kms near the poles and about 18 kms at the equator .
It contains about 75% of the total gaseous mass of the atmosphere and practically all the moisture and dust particles . The entire weather phenomenon happens in this sphere . Condensation , evaporation , precipitation , rainfall , cyclones etc ., occur in this layer .