592 TABLES 626-630.— THE ATMOSPHERE 



The atmosphere, with a total mass of about 5.3 X 10 21 g (about one-mil- 

 lionth the mass of the earth), extends 7,000-60,000 miles above sea level (de- 

 pending upon the definition of the top) and for purposes of discussion may be 

 divided into several regions or layers. From sea level up to about 10-15 km 

 (the troposphere), about the next 30 km above this (the stratosphere), and 

 the entire region above this (i.e., above about 40 km) is spoken of as the upper 

 atmosphere. At heights above 80 km in the upper atmosphere strong ioniza- 

 tion is found and thus this region is called the ionosphere. Again the iono- 

 sphere may be divided into three or four layers ; first, the E layer (about 100 

 km) moderately ionized; next the F x layer (at about 200 km) more strongly 

 ionized; the F 2 layer (about 300 km) much more strongly ionized. Above 

 this, there is some recent evidence indicating an additional ionized region, 

 the G layer (400-700 km). 



The following tables give some characteristics of the atmosphere as a 

 function of the height above sea level. 



TABLE 626.— COMPOSITION OF THE AIR NEAR GROUND LEVEL 181 



Molecular 

 Gas weight 



Nitrogen 28 



Oxygen 32 



Argon 40 



Carbon dioxide 44 



Neon 20.2 



Helium 4 



Krypton 83 



Hydrogen 2 



Xenon 130 



Ozone 48 



Radon 222 7 X IO" 18 , decreasing with altitude 



Water vapor 18 .2 — 4, variable 



m Regener, E., The structure and composition of the stratosphere, No. 509, Headquarters Air Materiel 

 Command, Wright Field, Dayton, Ohio, April 1946. 



TABLE 627.— COMPOSITION OF THE ATMOSPHERE UP TO THE F 2 LAYER, 



LATITUDE 45° 195 



188 Grimminger, G., Analysis of temperature, pressure and density of the atmosphere extending to 

 extreme altitudes, p. 18, Rand Corporation, November 1948. 



SMITHSONIAN PHYSICAL TABLES 



