Final answer:
An increased blood PCO2 level will lead to decreased blood pH as more hydrogen ions are produced, indicating elevated blood acidity.
Step-by-step explanation:
An increase in blood PCO2 will cause a decrease in blood pH. When carbon dioxide (CO2) in the blood increases, it reacts with water to form bicarbonate (HCO3-) and hydrogen ions (H+). The production of more hydrogen ions leads to a decrease in pH, also known as acidosis. This is because an increase in H+ concentration denotes increased acidity in the blood. As the level of carbon dioxide in the blood increases, more H+ is produced and the blood pH decreases. This increase in carbon dioxide and subsequent decrease in pH reduce the affinity of hemoglobin for oxygen, causing a shift in the oxygen dissociation curve to the right.