What Causes Acid Rain??

 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.

 The following are the stoichiometric equations for the formation of sulphuric acid

 Burning of fossil fuels emits sulphur dioxide.

 S (in coal) + O2SO2
 Sulphur dioxide reaches the atmosphere, it oxidizes to first form a sulphate ion.

 2 SO2 + O2 2 SO3
 The sulphate ion joins with hydrigen atoms in the air and becomes sulphuric acid. This then falls back down to earth as "acid rain"

 SO3 + H2O H2SO4

Oxidation occurs mostly in clouds, especially in heavily polluted air, where other compounds such as ammonia and ozone help to catalyze the reaction, converting more sulphur dioxide to sulphuric acid.

1997 Map of US Showing pH of precipitation

pH7.4-----------------------------pH5.4