Air contains water vapor, and the amount of water in a given mass of dry air, known as the mixing ratio, is measured in grams of water per kilogram of dry air (g/kg).
Aer vaporem aquaticum continet, et summa aquae in data aeris siccae massa contenta, in ratione mixturae appellata, est grammatis aquae per chiliogramma (g/kg) aeris siccae.WikiMatrix WikiMatrix