What are acid rains?

What are acid rains? â€Å"Acid rain is another side-effect of civilization. As soon as acid rain was discovered and understood, it was attributed to human action.† (Jurgen Stock, Arthur R. Upgren, p.4)Acid rain can be called any atmospheric precipitate (rain, snow, smog, rain with snows, etc) which has the following characteristics: the increased level of acids (mainly sulphuric acid); and the hydrogenous index of pH is less than average index of rain water (average pH for rain water is 5.6), mainly it is rain with pH