# Homework Help: Calculating maximum amount of water vapor per unit volume

1. Sep 17, 2011

### guitarstorm

1. The problem statement, all variables and given/known data

Compute the maximum amount of water vapor per unit volume that air can hold at the surface, where Ts = 288 K, and at a height of 10 km where T = 220 K. Express your answers in kg m-3.

2. Relevant equations

$e_{s}=Ae^{\beta T}$

$e=\rho _{v}R_{v}T$

3. The attempt at a solution

Since saturation occurs when e=$e_{s}$, I figured I would set the two equations equal to each other. However, solving for $\rho _{v}$ doesn't work... The units don't work out, and I get a really large number... I feel like I have to somehow relate this to the total pressure of the air, but I'm unsure how to go about this.

2. Sep 19, 2011

### guitarstorm

I was incorrect in my previous post saying that the units didn't work out... Solving for ${\rho _{v}}$ when e=$e_{s}$ does produce an answer in $\frac{kg}{m^{3}}$.... However I'm getting 1,103,248.397 $\frac{kg}{m^{3}}$, for the first case where T=288 K, which is way off from what I should be getting (0.0126 $\frac{kg}{m^{3}}$).

I believe I then have to use the ideal gas equation, pV=nRT, plugging in p for e... But this is where the confusion comes in. Hopefully someone can help me with this tonight, since this HW is due tomorrow morning...