ACID RAINDr. Vijaya Menon

INTRODUCTION

•Acid rain is used to describe all precipitation or deposition which is more acidic than normal. (pH< 5.6)

•Occurs when gaseous emissions of SOx and NOx interact with water vapour and sunlight.

•Produces a mixture of sulfuric acid, nitric acid and nitrous acids.

“Clean” or unpolluted rain has an acidic pH, but usually no lower than 5.7, because carbon dioxide and water in the air react together to form carbonic acid, a weak acid.. Carbonic acid is formed by the reaction

H2O (l) + CO2 (g) H2CO3 (aq)

Carbonic acid then can ionize in water forming low concentrations of hydronium and carbonate

ions:H2O (l) + H2CO3 (aq) HCO3− (aq)+ H3O

+ (aq)

CAUSESSOx and NOx emitted into the atm. are converted

into H2SO4 and HNO3 droplets by series of

photochemical and chemical reactions catalysed by

other species present in the atm.

SOx+O2+H2O H2SO3 or H2SO4

NOx+O2+H2O HNO2 or HNO3

Dry deposition: When these compounds along with organic and inorganic chemicals are deposited on earth as aerosols and particulates.

Wet deposition: When these compounds are carried to earth surface by precipitation.

Acid Deposition

NATURAL PHENOMENON

Volcanoes

Lightning

Biological decomposition

Forest fires

HUMAN ACTIVITIES

Human sources, such as

electricity generation

factories

motor vehicles

IMPACT ECOSYSTEM

Destroys food chain.

SURFACE WATER AND AQUATIC SYSTEMAcidification of streams and lakes.Reduced fish population.Effect on green algae.Rate of decomposition of aquatic matter is reduced.

SOIL, FOREST AND VEGETATIONAdversely affects growth of trees.Vanishing greenery.Leaching of plant nutrients like K.Foliar damage to crops.Alteration of seed germination characteristics.

Damage to young growing plants.Acidification of soil.Affects microbial and soil fauna.

MATERIALSCorrosion of metals.Damage to building and sculptural materials.CaCO3+H2SO4 CaSO4+H2O+CO2

Disintegration of textiles, paper, work of art.

HUMAN HEALTHEffects on lungs, skin, hair.Acidification of drinking water reservoirs, increase in heavy metal concentration exceed public health limits.

AFFECTED AREAS

Acidity in swedish lakes and rivers.

British parliament, St. Pauls Cathedral in London.

Lincoln Memorial, Michaelangelos statue of Marcus Aurelius.

Damage widespread in North America, Europe, Japan, China, SE Asia.

Taj Mahal.

Delhi, Agartala, Jamshedpur, Kolkata, Bhubneshwar, Chennai, Mumbai, Vadodra.

ACID RAIN IN THE UNITED STATES

Harvard

University wraps some

of the bronze and

marble statues on its

campus, such as this

"Chinese stele", with

waterproof covers every

winter, in order to

protect them from

erosion caused by acid

rain (or, actually, acid

snow.)

DESTRUCTION BY ACID RAIN

PREVENTIVE METHODS

Many coal-burning power stations use flue-gasdesulfurization (FGD) to remove sulfur-containing gases from their stack gases. For a typical coal-fired power station. FGD will remove 95 percent or more of the SO2 in the flue gases. An example of FGD is the wet scrubber which is commonly used.

Energy conservation.

Substiute for fossil fuels.

Catalytic converters in engines.

• In some areas the sulfates are sold to chemical companies as gypsum when the purity of calcium sulfate is high. In others, they are placed in landfill. However, the effects of acid rain can last for generations, as the effects of pH level change can stimulate the continued leaching of undesirable chemicals into otherwise pristine water sources, killing off vulnerable insect and fish species and blocking efforts to restore native life.

• Vehicle emissions control reduces emissions of nitrogen oxides from motor vehicles.