It can be observed that the atmospheric ari pressure can decrease from ~101 kPa to ~30 kPa at altitudes more than 10 KM from the meas sea level under constant temperature. The effect of change in the air pressure is explained using a simple analogy in Fig. 2.7. An empty (air-filled) plastic bottle was sealed at high altitude (~4.3 KM) and was brought to low altitudes. The bottle was observed to be defomed when it was brought to the lower altitudes (~2.7 KM). The bottle was completely crushed near the sea level (~0.3 KM) due to the increase in the atmospheric pressure compared to the air pressure inside the bottle.

The humidity also plays an influencing role on the air pressure. The effect of humidity is considered in the later part of this module which delas with the vapor.