Amagats
From the ideal gas law we can define the number of particles
at standard temperature (273.15 K) and standard pressure (1 atm =
1013.25 milli-bars). The ideal gas law can be written many ways, here
we will adopt the notation(s)
where, N is the number of molecules per unit volume, Boltzmann's constant k = 1.3806 · 10-16 erg/K, the gas constant
Rg = Na · k/<mw>, Avogadro's number, Na = 6.02 · 1023 particles per mole, <mw> is the molecular weight in grams/mole.
This number of molecules at STP is called Loschmidt's number and has the value,
The number of amagats of a gas is given as a ratio of the
actual number of particles at the given temperature and pressure to
Loschmidt's number. In planetary atmospheres the number density is a
function of height. We can calculate the thickness of an equivalent
atmospheric column at standard temperature and pressure. This is
denoted as cm-amagats or Km-amagats and is given by
Hydrostatic equilibrium relates the pressure and vertical coordinates
and the number density, Ni can be written as a function of the density,
where, qi is the volumetric fraction of species i.
Earth | Mars | Jupiter | Saturn | Titan | Uranus | Neptune | |
g | 981.0 | 374.1 | 2425.3 | 1000.0 | 136.0 | 880.1 | 1110.5 cm/s |
q(H2) | 1.00 | 1.00 | 0.90 | 0.96 | 1.00 | 0.85 | 0.85 |
<mw> | 28.97 | 44.01 | 2.22 | 2.14 | 28.00 | 2.30 | 2.30 gm/mole |
H0 | 7.88 | 13.61 | 37.45 | 100.50 | 58.85 | 94.08 | 74.56 Km-am/Bar |
1000/H0 | 126.9 | 73.49 | 26.70 | 9.95 | 16.99 | 10.63 | 13.41 mB/Km-am |