Renal compensation is a mechanism by which the kidneys can regulate the plasma pH. It is slower than respiratory compensation, but has a greater ability to restore normal values.
In respiratory acidosis, the kidney produces and excretes ammonium (NH4+) and monophosphate, generating bicarbonate in the process while clearing acid.
In respiratory alkalosis, less HCO3− is reabsorbed, thus lowering the pH.
References
Renal compensation Wikipedia(Text) CC BY-SA