VII. ALTITUDE

The temperature of the atmosphere is not uniform, but decreases with altitude up to 20 kilometers where it is found to be only 220°K. At altitudes above 20 km, the temperature is observed to increase with altitude as a result of the absorption of solar radiation by ozone in the upper atmosphere. At much higher altitudes the temperature decreases again. Any mountain climber knows there is a decrease of air density with altitude. At the highest permanently inhabited village in the Peruvian Andes, located at an altitude of 5.3 km, the air density is about half of the sea level density. In adapting to these conditions the inhabitants have developed unusually large lung capacities. Because of the exponential decreased of density with altitude, most of the atmospheric mass is beneath an altitude of 33 km, about three times the altitude of Mt. Everest.