Which is lighter – damp air or dry air?
Air gets lighter as it gets warmer. However, air also gets lighter as it becomes more humid. That is why we talk about water parts that are not visible (in gaseous form), not to be confused with mist (small drops of liquid water). Air essentially consists of a mixture of nitrogen and oxygen and has a molecular weight of approximately 29 grams, whereas the molecular weight of water vapour is only around 18 grams.
