Need help with Computing relative humidity?

Question

Air mass temp: 25 C with a relative humidity of 40%

I found the water vapor capacity to be: 24 g/m3 and the actual water vapor content to be 9.6 g/m3.

If the air were heated to 30 C, how do I compute the relative humidity?

If the air were cooled to 15 C, how do i computer the relative humidity?

Answer 1

One way is to use the Magnus formulas in ref. 1 to convert your RH & temperature to dewpoint, and then convert back from dewpoint to RH at the temperatures you need answers for. I would use the "over water" equations since your ambient temperatures are above freezing. Using a program I wrote for the purpose, I get 29.84% at 30 C and 74.35% at 15 C, but you'd better check. My dewpoint was 10.48 C.
EDIT: I found a calculator on the web. (But it doesn't tell you how it does it.) It agrees with my results closely. See ref. 2.