Humidity and downforce?

[Daniel]

Coulthard is saying that the cars give less downforce when it's humid, is this true?

[Rollo]

This is a physical chemistry question.

Dry air is more dense than moist air because moist air contains more water vapour. Water vapour is made of 2 hydrogens and and an oxygen, and is lighter than either oxygen gas or nitrogen gas which are the two most common components of the atmosphere.
Dry air at a constant temperature would create more pressure. Moist air at a constant temperature would create less pressure. Don't believe me? Check out the synoptic charts during the weather reports. A drop in pressure is almost always connected with rain.

More pressure = more downforce. Less pressure = less downforce. Coulthard is saying that the cars give less downforce when it's humid, is this true? Absolutely yes!

[Daniel]

Ah, fair enough then