The presence of CO2 may reduce the pH of rainwater up to
Right Answer is:
All rainwater is mildly acidic because ionization of at atmospheric carbon dioxide (CO2) that dissolves in it produces a solution with a pH of approximately 5-6 (compared with a neutral pH = 7.0. The acidity produced by CO2 can be significantly increased by the solution of sulfur and nitrogen oxides (SO2 and NO2). The pH of rainwater can range from quite acidic around 4.0 in industrial regions to about 5.6 in very clean regions.
When water moves through the subsurface, it equilibrates with soil gases and may become more acidic because of a higher soil concentration of dissolved CO2. Acidic groundwater has an increased capacity for dissolving minerals. The higher the CO2 concentration in soil air, the lower is the pH of groundwater.