Atmosphere (unit) for the purposes of specifying the physical properties of substances, “"standard pressure"” should be precisely . A pressure of 1 atm can also be stated as: Scuba divers and others use the word "atmosphere" and "atm" in relation to pressures that are relative to mean atmospheric pressure at sea level (1.013 bar). For example, a partial pressure of oxygen is calibrated typically using air at sea level, so is expressed in units of atm. The old European unit technical atmosphere (at) is equal to 1 kilogram-force per square centimetre (kgf/cm), Pa. Atmosphere (unit) The standard atmosphere (symbol: atm) is a
Henry's law a species in the aqueous phase, and formula_8 is the partial pressure of that species in the gas phase under equilibrium conditions. The SI unit for formula_12 is mol/(m Pa); however, often the unit M/atm is used, since formula_17 is usually expressed in M (1 M = 1 mol/dm) and formula_8 in atm (1 atm = 101325 Pa). The Henry solubility can also be expressed as the dimensionless ratio between the aqueous-phase concentration formula_17 of a species and its gas-phase concentration formula_24: For an ideal gas, the conversion is: where formula_27 is the gas constant and formula_28 is the temperature.