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How does carbon dioxide change the acidity around and inside cells?

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A pine grosbeak with pink and gray plumage perches on a branch, eating red berries among autumn foliage. — Chemoreception Animals, such as this pine grosbeak, use chemoreception to respond to chemicals that can be tasted and smelled in their environments. Many of these chemicals affect behaviors such as food preference and defense.

Carbon dioxide ( $C O_{2}$ ) influences acidity by acting as an acidic substance that readily dissolves in water to form carbonic acid ( $H_{2} C O_{3}$ ). This weak acid subsequently dissociates into hydrogen ions ( $H^{+}$ ) and bicarbonate ions ( $H C O_{3}^{-}$ ), a process that increases the concentration of hydrogen ions and thereby lowers the pH, making the environment more acidic.12

In the context of chemoreception and physiology, this mechanism functions as follows:

Extracellular and Intracellular Effects: Carbon dioxide increases the acidity of the fluid surrounding cells. Because $C O_{2}$ can easily pass through cell membranes, it also enters cells, where it can similarly increase the acidity of the intracellular environment.3
Physiological Regulation: The body monitors these changes to regulate breathing. While it remains unclear whether specific chemoreceptors respond primarily to intracellular or extracellular acidity, rising levels of $C O_{2}$ (and the resulting acidity) serve as a powerful stimulus for the respiratory system to increase ventilation, which helps eliminate excess $C O_{2}$ and restore pH balance.23