It is the lower most layer of atmosphere. It extends up to 18km at equator, 13 km at midlatitude and about 8km at poles.It contains approximately 90% of the total mass of the atmosphere.The entire weather phenomenon takes place in this layer. It contains all the watervapour, dust particles, clouds etc. In troposphere the temperature decreases with increase in height.The average rate of decrease of temperature with height is called normal lapse rate and it is equal to 6.4 degree C/km. the rate of decrease of temperature is not constanteverywhere.The local rate of decrease is called local lapse rate. The minimum temperature attainedin this layer is -57 degree C.Tropopause: It is the top most layer of troposphere. It acts as a boundary betweentroposphere and stratosphere. This layer is marked by constant temperatures.