e = Partial pressure of water vaour [Pa]
(after Murphy und Koop, Quart. J. Roy. Met Soc., 2005)

e = exp { 54.842763 - (6763.22 / T) - 4.21 * ln(T) + 0.000367 * T + tanh [ 0.0415 * (T - 218.8) ] *
       [ 53.878 - 1331.22 / T - 9.44523 * ln(T) + 0.014025 * T ] }

valid in range 123 K < T < 332 K

T = temperature [K]

T from °C to °C

Vapour pressure calculation

T: K     

e: Pa