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Temperature T is in °C and vapour pressure P is in kilopascals (kPa). The coefficients given here correspond to equation 21 in Alduchov and Eskridge (1996). [2] See also discussion of Clausius-Clapeyron approximations used in meteorology and climatology. Tetens equation
The Antoine equation is a class of semi-empirical correlations ... (760 mmHg = 101.325 kPa ... For switching from degrees Celsius to kelvin it is sufficient to ...
where temperature T is in degrees Celsius (°C) and saturation vapor pressure P is in kilopascals (kPa). According to Monteith and Unsworth, "Values of saturation vapour pressure from Tetens' formula are within 1 Pa of exact values up to 35 °C." Murray (1967) provides Tetens' equation for temperatures below 0 °C: [3]
One pascal is one newton per square meter (N·m −2 or kg·m −1 ·s −2). Experimental measurement of vapor pressure is a simple procedure for common pressures between 1 and 200 kPa. [2] The most accurate results are obtained near the boiling point of the substance; measurements smaller than 1 kPa are subject to major errors. Procedures ...
Pressure as a function of the height above the sea level. There are two equations for computing pressure as a function of height. The first equation is applicable to the atmospheric layers in which the temperature is assumed to vary with altitude at a non null lapse rate of : = [,, ()] ′, The second equation is applicable to the atmospheric layers in which the temperature is assumed not to ...
The pascal (Pa) or kilopascal (kPa) as a unit of pressure measurement is widely used throughout the world and has largely replaced the pounds per square inch (psi) unit, except in some countries that still use the imperial measurement system or the US customary system, including the United States.
For example, IUPAC has, since 1982, defined standard reference conditions as being 0 °C and 100 kPa (1 bar), in contrast to its old standard of 0 °C and 101.325 kPa (1 atm). [2] The new value is the mean atmospheric pressure at an altitude of about 112 metres, which is closer to the worldwide median altitude of human habitation (194 m).
The conversion equations depend on the temperature at which the conversion is wanted (usually about 20 to 25 degrees Celsius). At an ambient air pressure of 1 atmosphere (101.325 kPa), the general equation is: = / ()