import math


def solubility_time(init_s, time, a = -0.1/3600):
    """
    Return the solubility as a time fonction [kg/m³]
    source : (Shen et al., 1993)

    Parameters
    ----------
    init_s : Initial solubility [kg/m³]
    time : Time from the start of the oil spill [s]
    a : Parameter of the exponential, the default is -0.1/3600.


    """
    return init_s * math.exp(a * time)