Surface density structure in inner regions of the TW Hya model. δ_gas is the inner disk drop in gas surface density. The value δ_gas = 0.1 used here best fits the H₂ observations. The red curves show the column averaged oxygen and carbon depletion factors in TW Hya. The red solid line shows a model with constant depletion. The dotted line shows the depletion profile assuming that carbon and oxygen return to the ISM values above T_gas = 150 K.