partial pressure, the pressure exerted by any one gas in a mixture of gases or in a liquid, with the pressure directly related to the concentration of that gas to the total pressure of the mixture. The concentration of oxygen in the atmosphere represents approximately 21% of the total atmospheric pressure, calculated at 760 mm Hg under standard conditions. Therefore, the partial pressure of atmospheric oxygen is about 160 mm Hg (760 mm Hg × 0.21).
