Often the notion of air holding water vapor is presented to describe the concept of relative humidity. This, however, is a misconception. Air is a mixture of gases (nitrogen, oxygen, argon, water vapor, and other gases) and as such the constituents of the mixture simply act as a transporter of water vapor but are not a holder of it.
Relative Humidity is defined in terms of only the physical properties of water and thus is unrelated to the notion of air holding water. In fact, an air-less volume can contain water vapor and therefore the humidity of this volume can be readily determined.
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