Here's why:
* Natural Rainwater: Pure rainwater is slightly acidic, with a pH around 5.6. This acidity is due to the dissolution of atmospheric carbon dioxide.
* CO2 and Carbonic Acid: When CO2 dissolves in water, it forms carbonic acid (H2CO3). This acid then dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-), contributing to the acidity of rainwater.
* pH and Acidity: The pH scale measures acidity, with lower pH values indicating higher acidity. A pH of 6.0 is slightly less acidic than the natural rainwater pH of 5.6.
Therefore, a higher concentration of CO2 in the atmosphere would lead to more carbonic acid formation and subsequently, a lower pH value (closer to 6.0) in rainwater.
