Humid air is actually less dense than dry air, as any aircraft pilot should be able to tell you. That's because the water molecule H2O has a molecular weight of

Humid air is actually less dense than dry air, as any aircraft pilot should be able to tell you. That's because the water molecule H2O has a molecular weight of 18, while O2 has a molecular weight of 32 and N2 has a molecular weight of 28.