DIELECTRIC CONSTANT OF MOIST AIR 3 



line of oxygen. For non-polar gases (n = 0), this equation becomes 



e - 1 M _ 4TNao 



6 + 2 p " 3 ^^-"^^ 



which is well approximated by 



e - 1 ^ ^ 4:irNao (1.4) 



for gases at low pressures. 



This equation may be rewritten, by assuming the perfect gas law, as 



e-l =K[^ (1.5) 



where K[ is a constant. The result for polar gases, (1.2), may be written 



(1.6) 

 which, assuming (1.5), can be rewritten as 



e- 1 ::=K^|(a +|) (1.7) 



where K'^, A, and B are constants. For a mixture of gases, Dalton's 

 law of partial pressures is assumed to hold with the result that we can 

 sum the effects of polar and non-polar gases and hence obtain 



e - 1 =« 1^ 47riV 

 M 



2 



"" + SkTA 



— 1 = 2] K'li -^ + 22 ^20 i^[Ag-{--~]- (1 



•8) 



For the troposphere, however, we need only consider the effects of 

 CO2, dry air (non-polar gases), and water vapor (a polar gas) such that 



e - 1 = K,\ :^ + AV, I ( A + I ) + K{, ^ (1.9) 



where Pd is the pressure of dry air, c is the partial pressure of water vapor, 

 and Pc the partial pressure of CO2. The equation for refractive index, n, is 

 obtained using the expression n = a/m^, where ^i, the permeability, may 



