4.5 A layer of soil (pseudo-component B) of thickness 1m (see figure) that is located above a clay barrier has been contaminated with a toxic gas (A). The concentration of the gas is initially uniform in the soil and equal to 1.0105mol/cm3. The toxic gas will be removed by making pure air flow over the surface of the soil. The air velocity is such that the convective mass transfer coefficient for the transport of A from the surface of the soil to the bulk air flow is 0.001cm/s. The diffusivity of the toxic gas in the soil is 0.05cm2/s, and its partition coefficient (ratio of concentration of A in air to concentration of A in soil at equilibrium) is 2.5 . You might assume that A does not diffuse into the clay barrier. a. Determine the time necessary to remove 99% of the toxic gas from the soil. b. Representatives from the company in charge of the clean-up process claim that by increasing the air velocity, the clean-up time can be reduced from the value calculated in part (a) to 2 days. Assess the veracity of the claim. Air flow