At these conditions, the binary molecular diffusion coefficient of CO2 in air is 0.161 cm2 /s, but the effective diffusion coefficient of CO2 within the porous medium is only 0.011 cm2 /s. Fresh air containing no CO2 blows over the surface of the slab so that the convective mass transfer coefficient for CO2 (kc) is 0.0037 cm/s. Use the appropriate concentration-time chart to determine at what depth from the surface in the porous material the CO2 will be 3.0 mole% after a period of 30 minutes.