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I am looking for a reference (e.g. book, peer-reviewed paper) that asserts that absolute humidity is "equivalent" to the dew-point temperature.

Such statement should be true, AFAIU. Online, people say they are the same, in scientific publications they look almost linearly related in some range of temperatures here, figure 4, I tested their relation on data I have and their correlation is $ > 0.98$.

But I am unable to find a reference that states the absolute humidity and the dew-point temperature are "equivalent", "highly correlated (under reasonable conditions)", or that "one can serve as a proxy for the other". Please help me find such reference.

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They're not directly equivalent. I think the problem is that "absolute humidity" is used to mean both "a measurement of the actual humidity content of the air" ("absolute" as in "non-relative") and, in some sources, "mass of water vapor per unit volume" - which is temperature-dependent as well (using $PV=nRT$ at fixed pressure and mass: $V$ varies with $T$).

I think this technical note covers it. Key points:

  • Vapor pressure is a function of dew point alone (Eq. 16 - remaining variables are constants).
  • Absolute humidity is a function of vapor pressure and temperature (Eq. 3).
  • Thus, absolute humidity is a function of both dew point and temperature (Eq. 20).

The reason they appear to be directly related, like in the dataset you looked at, is that $T$ (in Kelvin) only varies by 20% or so in a typical temperature range (e.g., -20 to +40 C = 253 to 313 K), so it doesn't affect things that much.

That technical note does work as a citation for dew point being an absolute measurement of humidity, since it corresponds directly to vapor pressure in Eq. 16.

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