1
$\begingroup$

I've been looking around for a way to calculate the humidity ratio by the partial vapor pressure and the atmospheric pressure of the environment.

I found a procedure for such calculation on engineering toolbox (https://www.engineeringtoolbox.com/humidity-ratio-air-d_686.html). There, it is explained that:

Based on the Ideal Gas Law, the humidity ratio can be expressed as:

x = 0.62198 pw / (pa - pw)

where

pw = partial pressure of water vapor in moist air (Pa, psi)

pa = atmospheric pressure of moist air (Pa, psi)

However, it is very unclear to me where they got the value 0.62198 from. I couldn't find any explanation as to why this value is used and how is it obtained.

Improve this question
$\endgroup$

1 Answer 1

Reset to default
0
$\begingroup$

It is the ratio between the molar mass of water (about 18.01528g/mol) and the one of dry air (about 28.97g/mol).

Improve this answer
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.