Acid Rain

The major gaseous pollutants are

SO₂ from coal burning power plants and industrial processes
NO₂ and NO (called NO_x) from automobile exhaust gases
CO₂ from manufacturing industries

CO₂ is usually found in small amounts in the atmosphere. CO₂ reacts with water to form a weak acid called carbonic acid and leads to rainwater being slightly acidic :

CO₂ (g) + H₂O (l) ---> H₂CO₃ (aq)
H₂CO₃ (aq) ---> H⁺ (aq) + HCO₃^- (aq)

SO₂ is oxidized in the atmosphere to SO₃ (g) and reacts with moisture to form sulfuric acid, H₂SO₄ :

SO₂ (g) + O₂ (g) ---> SO₃ (g)
SO₃ (g) + H₂O (l) ---> H₂SO₄ (aq)

NO₂ reacts with moisture to form nitric and nitrous acid :

NO₂ (g) + H₂O (l) ---> HNO₃ (aq) + HNO₂ (aq)

                  nitric + nitrous acid

Due to all these acids forming in the atmosphere, the rain becomes very acidic - called acid rain. Values as low as pH 2 has been recorded in Wheeling, WV ( due to coal operations )

Additional consequences of excessive pollution

Fogs act as concentrator - leads to severe damage of forests
Nitric acid influences nutrient effect by acting as fertilizer year round - plants keep growing during cold seasons and die.

Neutralization of the acids can take place in the ground if limestone (CaCO₃) is present :

CaCO₃ + H₂SO₄ ---> CaSO₄ + H₂O + CO₂

Most old building and statues are made of limestone and have seen accelerated deterioration in the last 25 years

Industrial remedies

Gas can be "scrubbed" in a scrubber - a column where the gas is cleaned by reacting the gas with Ca(OH)₂ which acts as neutralizing agent :
Ca(OH)₂ + H₂SO₄ ---> CaSO₄ + H₂O
catalytic converter on automobiles react the exhaust gases to CO₂ and N₂

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