Table 1a, Table 1b, and Table 1c present the total emissivity of water vapor, carbon dioxide gas, and a mixture as a function of P_aL and T_g. The quantity is the partial pressure of the absorbing gas, H₂O or CO₂; L is the beam length of concern; and T_g is the gas temperature. The tables for the individual gases are presented for an equivalent broadening pressure ratio P_e of 1. The ratio is defined in the footnote to Table 1a and accounts for the fact that collisions between absorbing molecules and foreign gas molecules are less effective in broadening the absorption lines than absorber-absorber collisions. In the case of Table 1c the total pressure of the mixture is 1 atm. and the absorber partial pressure P_a is that of the H₂O component in the mixture.

The tables are based on the information contained in Table 5-1 of Section 208 in the manner illustrated there in the sample calculations.

The emissivity grows with P_aL because at constant T_s the number of absorbing molecules increases as P_aL increases. At low values of P_aL the emission is weak, and each additional molecule adds equally to the absorption; hence ε_g is linear in P_aL. At higher values the addition of greater opacity at the centers of the lines has little additional effect there, but more is emitted between the lines. The ε_g integrated over the lines grows as \(\sqrt{P_a L}\). At still higher values of P_aL, the addition of greater opacity even between the lines near the center of the absorption-emission band has little additional effect there, and ε_g grows primarily in the tails of the bands, in total even more slowly. Logarithmic interpolation in Table 1a, Table 1b, and Table 1c is recommended as follows:

\(\epsilon_{g}(P_{a}L) = \epsilon_{g}(P_{a}L_{2})\left(\frac{P_{a}L}{P_{a}L_{2}}\right)^{n}\notag\)

\(n = \frac{\log[\epsilon_{g}(P_{a}L_{2})/\epsilon_{g}(P_{a}L_{1})]}{\log(P_{a}L_{2}/P_{a}L_{1})}\notag\)