To manage this tradeoff between local pH and local carbon concentration, the bulk pH determined from FEM to optimize CO2R at 1% CO2 increases to 7.5 (Figure ), a result confirmed experimentally. As CO2 concentrations are reduced, the bulk pH that leads to the greatest improvement in enzymatic CO2R with CA present can be shown by FEM to move to more basic values as the importance of increased substrate concentration outweighs the requirement to optimize the local pH for optimal activity (Figure ). This improvement in enzymatic CO2R is contingent on the presence of CA as without fast CO2 hydration kinetics, the increased local HCO3 -concentrations cannot be used to elevate local substrate concentrations and the more basic bulk pH is merely detrimental to the activity of FDh.