The binding of carbon dioxide with haemoglobin is related to partial pressure of CO2. The partial pressure of O2 is a major factor which can affect this binding. In the tissues, pCO2 is higher than pO2 and hence more binding of carbon dioxide occurs at the tissue level. In the alveoli, pCO2 is lower than pO2 and hence dissociation of carbamino-haemoglobin takes place in the alveoli.