Does humidity affect air density?

[khaichou]

Hi, as the topic stated, i would like to find out, does the humidity in the air affect the density??
thanks

 

[minger]

I wouldn't see how it couldn't. I would think you would need to do a partial pressures analysis to see the water content (prolly involving a psychometric chart). Then using a ratio of densities of water/air at that temperature to get the overall density.

But this is definitely just a guess.

 

[BobG]

The molar mass of air is almost 29. The molar mass of water is 18. The more 'less dense' gas you have intermixed into the air, the less dense the air. So, yes, humid air is less dense than dry air.

 

[DaveC426913]

My gut tells me that humid air is more dense than dry air.
(edit)
My gut, apparently lies:

http://www.usatoday.com/weather/wdensity.htm
"Most people who haven't studied physics or chemistry find it hard to believe that humid air is lighter, or less dense, than dry air."

BobG seems to be right on the money.

 

[Astronuc]

The molar mass of air is almost 29. The molar mass of water is 18. The more 'less dense' gas you have intermixed into the air, the less dense the air. So, yes, humid air is less dense than dry air.

That's exactly it - diatomic molecules N₂ and O₂ have approximate molecular masses of 28 and 32 (and air is 78+% N and 21+% O with traces of other gases), which in humid air are displaced by H₂O, which has a molecular mass of 18.