Case Studies ofCase Studies of Scientific and Technological Issues Scientific and Technological Issues

Nature and Development of Science and Nature and Development of Science and TechnologyTechnology

Acid Rain and its EffectsAcid Rain and its Effects

Concepts of AcidityConcepts of Acidity

Acidity of some everyday objects on the pH scale

Normal rainwater shows pH of about 5.6 because of the

reaction of carbon dioxide with water to form a weak

carbonic acid.

What is Acid Rain?What is Acid Rain?

Basically, rain water is considered Basically, rain water is considered as acidic when it’s pH value lower as acidic when it’s pH value lower than 5.6than 5.6

What is Acid Rain?What is Acid Rain?

Causes of Acid Rain?Causes of Acid Rain?

Sulphur DioxideSulphur Dioxideandand

Nitrogen OxidesNitrogen Oxides……

…the pollutants hiding …the pollutants hiding behind Acid Rainbehind Acid Rain

Sulphur DioxideSulphur Dioxide

Sulphur occurs widely in nature, in all animal and Sulphur occurs widely in nature, in all animal and plants, and in the plants, and in the fossil fuelsfossil fuels

When fossil fuels are burned to generate energy When fossil fuels are burned to generate energy the sulphur combines with the oxygen in the the sulphur combines with the oxygen in the atmosphere to form sulphur dioxide.  atmosphere to form sulphur dioxide. 

In many urban and industrial areas human In many urban and industrial areas human activity may account for around 90 percent of the activity may account for around 90 percent of the SO2 in the air.SO2 in the air.

Sulfur dioxide oxidizes in the atmosphere and Sulfur dioxide oxidizes in the atmosphere and reacts with water to produce sulfuric acid which reacts with water to produce sulfuric acid which eventually falls as acid raineventually falls as acid rain

Sulphur DioxideSulphur Dioxide

About 20 million tons of sulfur dioxide are emitted into the atmosphere from the United States each year

Nitrogen OxidesNitrogen Oxides

A number of different kinds of nitrogen oxides A number of different kinds of nitrogen oxides exist in the atmosphere. Collectively they are exist in the atmosphere. Collectively they are given the name NOx.  given the name NOx. 

In industrial areas, the vast majority are produced In industrial areas, the vast majority are produced when fossil fuels are burned.  when fossil fuels are burned. 

The nitrogen present in the fuel and in the The nitrogen present in the fuel and in the atmosphere combines with oxygen to produce atmosphere combines with oxygen to produce several different types of NOx.  several different types of NOx. 

Coal-burning power stations and transport are the Coal-burning power stations and transport are the major sources.major sources.

Nitric oxides also oxidize in the atmosphere and Nitric oxides also oxidize in the atmosphere and react with water to produce nitric acid which react with water to produce nitric acid which eventually falls as acid raineventually falls as acid rain

Nitrogen OxidesNitrogen Oxides

About 25 million tons of nitrogen oxides are emitted into the atmosphere from the United States each year

SOURCES

GaseousPollutants inAtmosphere

Pollutants inCloud Water

andPrecipitation

WetDeposition

ParticulatePollutants inAtmosphere

RECEPTORS NaturalAnthropogeic

VOCSO2

NOX

Hg

VOCNOX

Dry

Deposi

tion

Dry

Deposi

tion

SOURCES

GaseousPollutants inAtmosphere

Pollutants inCloud Water

andPrecipitation

WetDeposition

ParticulatePollutants inAtmosphere

RECEPTORS NaturalAnthropogeic

VOCSO2

NOX

Hg

VOCNOX

Dry

Deposi

tion

Dry

Deposi

tion

• Acid rain forms when pollutants (e.g. SO2 and NOx) combine with water in the atmosphere and fall to the earth as rain

Acid Rain in Hong KongAcid Rain in Hong Kong

From the fading view across Victoria Harbour to the poor qFrom the fading view across Victoria Harbour to the poor quality of the air we breathe, air pollution is having a growing uality of the air we breathe, air pollution is having a growing impact on our lives…….impact on our lives…….(Environment Hong Kong 1999)(Environment Hong Kong 1999)

MingPao News 24 June 1999MingPao News 24 June 1999

MingPao News 24 June 1999MingPao News 24 June 1999

MingPao News 24 June 1999MingPao News 24 June 1999