Gas constants

From Glossary of Meteorology
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gas constant

The constant factor in the equation of state for ideal gases.

The universal gas constant is
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The gas constant for a particular gas is
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where m is the molecular weight of the gas. For a mixture, the "molecular weight" is a weighted mean of the molecular weights of the components:
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where m1, · · ·, mn are the molecular weights of the n gases, and f1, · · ·, fn are their masses relative to the total mass of the mixture. The gas constant for dry air is

Rd = 2.870 × 102 J/(kg*K)

The gas constant for water vapor is

Rd = 4.615 × 102 J kg-1K-1

For moist air, the variable percentage of water vapor is taken into account by retaining the gas constant for dry air while using the virtual temperature in place of the temperature.
See also Boltzmann's constant.