CO2buffering

CO2 buffering refers to the chemical and physiological processes that resist changes in pH caused by fluctuations in carbon dioxide. The bicarbonate buffer system is the most important buffer in many biological fluids, linking CO2 metabolism to acid-base balance.

In water, CO2 dissolves and reacts: CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3−. The interconversion is rapid, and carbonic anhydrase enzymes accelerate the reactions in many tissues. The pH of a solution is influenced by the ratio of bicarbonate to dissolved CO2, commonly described by the Henderson-Hasselbalch equation: pH = pKa + log([HCO3−]/(0.03 × pCO2)).

In physiology, buffering operates on multiple time scales. The respiratory system provides short-term buffering by adjusting ventilation to modulate pCO2; the kidneys offer longer-term buffering by reabsorbing or excreting bicarbonate and by generating new bicarbonate. Normal arterial pH is about 7.35–7.45, arterial pCO2 around 40 mmHg, and bicarbonate near 24 millimoles per liter. Other buffers, such as phosphate and intracellular proteins, contribute to buffering, especially within cells.

In environmental science, ocean buffering involves the carbonate system, including CO2, H2CO3, HCO3−, and CO3^2−. Alkalinity and temperature influence buffering capacity. Rising atmospheric CO2 lowers seawater pH and alters carbonate speciation; while buffering mitigates some pH change, it does not prevent acidification and long-term ecosystem impacts.

Understanding CO2 buffering informs medicine, physiology, and climate-related chemistry, and helps diagnose acid-base disorders as well as evaluate changes in aquatic environments.