![]() The uncertainties associated with these equations are: (Formulae due to Sonntag, 1990, updated from formulae given by Wexler, 19.) This is a more accurate but complex alternative formula for vapour pressure (in pascals) from dew point (in kelvin) for water: ![]() Ln e i(t) = ln 611.2 + (22.46 t)/(272.62+ t) (Equation 3)įor the range -65 ☌ to +0.01 ☌, values given by this equation have an uncertainty of < ☑.0 % of value, at the 95% confidence level. Ln e w(t) = ln 611.2 + (17.62 t)/(243.12+ t) (Equation 2)įor information, 100 Pa = 1 millibar (mbar)įor the range -45 ☌ to +60 ☌, values given by this equation have an uncertainty of < ☐.6 % of value, at the 95% confidence level. Vapour pressure can be calculated using the Magnus formula. This states that at a temperature t (in ☌), the saturation vapour pressure e w(t), in pascals (Pa), over liquid water, is Use Equation 2 or 3 below (or Equation 4 or 5) to calculate dew or frost point temperature from vapour pressure (requires iteration if using Equations 4 or 5).Use Equation 1 to calculate water vapour pressure from saturation vapour pressure and known relative humidity. ![]()
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