General concepts on

ACID RAIN

Tareq Bin AzirLecturer- Department of ChemistryGovernment Titumir CollegeDhakatareqbinazir@yahoo.com

Definition

Sources

Formation

Deposition

Affected Areas

Effects

Preventive Measures

Contents:

Definition of Acid Rain

• Rain water that has a pH of less than that of natural rainwater (<5.6)

• It is formed when

1. sulfur dioxide and sulfur trioxide (SO2 ; SO3)

2. nitrogen monoxide and nitrogen dioxide (Nox) gases in the atmosphere, combine with water vapor

and precipitate as Sulfuric acid(H2SO4) or Nitric acid(HNO3)

• This acidic precipitation then falls to the earth as rain, snow or fog

pH Scale

pH = -log[H+]

pH & WATER

• Pure water is neutral • Sea water is slightly basic • Normal rainfall is slightly

acidic due to carbon dioxide (CO2) mixing with water vapor forming carbonic acid

• Acid rain is acidic

Sources of Acid Rain

• Natural Sources – – Emissions from volcanoes and biological processes that

occur on the land, in wetlands and in the oceans contribute acid-producing gases to the atmosphere

– Effects of acidic deposits have been detected in glacial ice thousands of years old in remote parts of the globe

Human Sources of Acid Rain

Industrial factories, power-generating plants and vehicles

Sulfur dioxide and oxides of nitrogen are released during the fuel burning process (i.e. combustion)

Sulfur dioxide accounts for about 90 % of all acid rainfall

Formation of Acid Rain

Formation of Sulfuric Acid (H2SO4)2SO2(g) + O2(g) 2SO3(g)

SO3(g) + H2O(l) H2SO4(aq)

2NO(g) + O2(g) 2NO2(g)

4NO2(g) + 2H2O(l) + O2(g) 4HNO3(aq)

Formation of Nitric Acid (HNO3)

Acid deposition

Wet depositionWet deposition of acids occurs when any form of precipitation (rain, snow and so on) removes acids from the atmosphere and delivers it to the Earth's surface. This can result from the deposition of acids produced in the raindrops.Dry depositionAcid deposition also occurs via dry deposition in the absence of precipitation. This can be responsible for as much as 20 to 60% of total acid deposition. This occurs when particles and gases stick to the ground, plants or other surfaces.

Effects of Acid Rain

Harmful on aquatic life Increased acidity in water bodies Stops eggs of certain organisms (e.g. fish) to

stop hatching Changes population ratios Affects the ecosystem

Effects on Vegetation Harmful to vegetation Increased acidity in soil Leaches nutrients from soil, slowing plant

growth Leaches toxins from soil, poisoning plants Creates brown spots in leaves of trees,

impeding photosynthesis Allows organisms to infect through broken

leaves

Effects on Buildings and Structures

• Marble is particularly susceptible• Accelerates weathering in metal and

stone structures– Eg. Parthenon in Athens,

Greece; Taj Mahal in Agra, India Effects on Human Health• Respiratory problems, asthma, dry

coughs, headaches and throat irritations

• Brain damage, kidney problems, and Alzheimer's disease has been linked to people eating "toxic" animals/plants

Affected Areas

– Acid rain is a problem in Eastern Canada and the Northeastern USA

– Acid rain from power plants in the Midwest United States has also harmed the forests of England.

– Industrial acid rain is a substantial problem in China, Taiwan, Eastern Europe, Russia and areas down-wind from them.

– The effects of acid rain can spread over a large area, far from the source of the pollution

Prevention Using alternative sources of electricity

(i.e. nuclear power, hydro-electricity, wind energy and solar energy)

Minimize fossil fuel use in power plants, factories, vehicles etc.

Reduce the amount of electricity use Energy Conservation & Change life

style

Use catalytic converters in vehicle exhausts which remove the nitrogen oxides.

Limit the number of vehicles on the roads and increase public transport.

THANK YOU