Effects of carbon dioxide and humidity on some acoustic and thermodynamic properties of air

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The theoretical data on the combined effects of humidity and carbon dioxide content on some physical properties of air, such as the characteristic impedance ρc and the sound speed c, the specific heats Cp and Cv, and their ratio γ, and the density ρ, have been studied. In general, over the temperature range 0°–30 °C, the normalized values Cp/(Cp)0, Cv/(Cv)0, and c/c0, become larger with the inclusion of humidity and rising temperature; and they are also inversely proportional to the CO2 content. Similarly, ρ/ρ0 and ρc/(ρc)0 are proportional to the CO2 content, but they are inversely proportional to humidity and temperature. However, the normalized value γ/γ0 becomes smaller with the increase of humidity, temperature, and CO2 content. The above reference values, which are indicated with a zero suffix, such as (Cp)0 and ρ0, refer to dry standard air (314 ppm CO2 content) at 0 °C and at a pressure of 101.325 kPa.