PPT Slide
Unpolluted rain is itself slightly acidic with a pH level of about 5.6.
Results from the dissolution of CO2 (an acidic oxide) in water droplets
CO2 (g) + H2O(l) H2CO3 (aq)
H2CO3 (aq) H+ (aq) + HCO3-(aq)
CO2 (g) + H2O(l) H+ (aq) + HCO3- (aq)