Mass Fraction of Water Vapor or Specific Humidity

2 Mass Fraction of Water Vapor or Specific Humidity 

Another dimensionless physical quantity is the mass fraction of water vapor in moist air, sometimes called specific humidity denoted, w or, less often q, i.e., the ratio of the mass of water vapor over the masses of both air and water vapor. The relationship between the absolute humidity and water mass fraction is described by the following equation  

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