Acid rain is customary to call ANY (precipitation as rain, snow, hail), containing any number of acids. The presence of acid leads to a decrease in pH. Hydrogen, Terp (pH) - the value depicting the concentration of hydrogen ions in solution. The lower the pH, the more hydrogen ions in the solution, the more acidic is the rain sreda.Kislotnye nature of its origin are of two types: natural (arise from the very nature of the activity) and anthropogenic (human-caused).