Rain water sometimes contain traces of acid. Why?
Answers
Scientists have discovered that air pollution from burning of fossil fuels is the major cause of acid rain.
The main chemicals in air pollution that create acid rain are sulfur dioxide (SO2) and nitrogen (NOx).
Acid rain usually forms high in the clouds where sulfur dioxide and nitrogen oxides react with water, oxygen, and oxidants. this mixture forms a mild solution of sulfuric acid and nitric acid.
Sunlight increases the rate of most of these reactions. Rainwater, snow, fog, and other forms of precipitation containing those mild solutions of sulfuric and nitric acids fall to earth as acid rain.
Acid rain does not account for all of the acidic particles and gases onto buildings, cars, home, and trees.
In some instances, these gases and particles can eat away the things on which they settle. dry deposited gases and particles are sometimes washed from trees and other surfaces by rainstorms.
When that happens, the runoff water adds those acids to the acid rain, making the combintion more acidic that the falling rain alone. the combination of acid rain plus dry depostied acid is called acid deposition.
short and sweet answer is
the accumulation of sulfur and nitrogen oxides.