def saturated_vapor_pressure(t_kelvin):
    """Saturated Vapor Pressure (Pa) at t_kelvin (K).

    This function accounts for the different behaviour above vs. below
    the freezing point of water.

    Note:
        [1] W. Wagner and A. Pru:" The IAPWS Formulation 1995 for the Thermodynamic
        Properties of Ordinary Water Substance for General and Scientific Use ",
        Journal of Physical and Chemical Reference Data,
        June 2002 ,Volume 31, Issue 2, pp. 387535

        [2] Vaisala. (2013) Humidity Conversion Formulas:
        Calculation Formulas for Humidity.
        www.vaisala.com/Vaisala%20Documents/Application%20notes/Humidity_Conversion_Formulas_B210973EN-F.pdf
    """

    if t_kelvin >= 273.15:
        # Calculate saturation vapor pressure above freezing
        sig = 1 - (t_kelvin / 647.096)
        sig_polynomial = (-7.85951783 * sig) + (1.84408259 * sig ** 1.5) + \
            (-11.7866487 * sig ** 3) + (22.6807411 * sig ** 3.5) + \
            (-15.9618719 * sig ** 4) + (1.80122502 * sig ** 7.5)
        crit_temp = 647.096 / t_kelvin
        exponent = crit_temp * sig_polynomial
        p_ws = math.exp(exponent) * 22064000
    else:
        # Calculate saturation vapor pressure below freezing
        theta = t_kelvin / 273.15
        exponent = -13.928169 * (1 - theta ** -1.5) + \
            34.707823 * (1 - theta ** -1.25)
        p_ws = math.exp(exponent) * 611.657
    return p_ws
Saturated Vapor Pressure (Pa) at t_kelvin (K).

    This function accounts for the different behaviour above vs. below
    the freezing point of water.

    Note:
        [1] W. Wagner and A. Pru:" The IAPWS Formulation 1995 for the Thermodynamic
        Properties of Ordinary Water Substance for General and Scientific Use ",
        Journal of Physical and Chemical Reference Data,
        June 2002 ,Volume 31, Issue 2, pp. 387535

        [2] Vaisala. (2013) Humidity Conversion Formulas:
        Calculation Formulas for Humidity.
        www.vaisala.com/Vaisala%20Documents/Application%20notes/Humidity_Conversion_Formulas_B210973EN-F.pdf