notes on chapter water class 8
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Introduction to Air Pollution
In chapter 18 of class 8 Science, we study the harmful changes taking place in our surroundings and their effects on our lives. The substance that contaminates air and water are known as pollutants. Air gets polluted from natural sources smoke and dust arising from forest fires or volcanic eruptions. Pollutants such as power plant and automobile exhaust and burning of firewood are man-made pollutants. Carbon dioxide, nitrogen oxides, carbon monoxide, methane and sulphur dioxide are the major pollutants of air. Increasing levels of carbon dioxide lead to global warming.
Pollution
Environmental pollution refers to undesirable changes in the surroundings that have adverse effects on plants, animals and other biological and physical components of the environment.
A substance that causes pollution is called a pollutant. Pollutants can be in liquid, solid or gaseous form.
A substance becomes a pollutant when its concentration is greater than the natural abundance and this increase in concentration is either due to human activities or natural phenomenon.
Types of pollution: Air pollution, water pollution, soil pollution, sound .
Air Pollution
Air pollution is the introduction of pollutants, organic molecules, or other hazardous substances into earth’s atmosphere.
Sources:
a) Natural – forest fire, dust storms, and volcanic activity
b) Man-made – power plants, homes, industries, oil refineries, and transportation
Effects:
Causes allergies, diseases and even death to humans.
Causes birth defects in new-born babies.
Endangers animal health and welfare of plants and vegetation.
To know more about Air Pollution, visit here.
How Crucial Is Air and Water?
Water
The major sources of water are streams, rivers, lakes, oceans on the earth’s crust.
It plays a significant role in sustaining life on earth.
It is widely used for human activities such as agriculture, drinking, washing, cleaning, etc.
Air
Air is inevitable in our lives.
The oxygen in the air is essential for the animals to survive.
Oxygen helps to produce energy in their bodies.
Air Pollution – What and How
Air Pollutants
The substances, which accumulate in the air in high enough concentration that is hazardous to all organisms or to materials exposed to the air are called air pollutants.
These may be present as solid particles, liquid droplets or gases.
Examples: Methane, chlorofluorocarbons, particulate matter, sulphur dioxide, nitrogen dioxide, carbon monoxide, lead, etc.
Carbon Dioxide and Carbon Monoxide
Sources of carbon dioxide: cement production, deforestation and burning of fuels like gasoline, natural gas, oil, coal, and wood.
Sources of carbon monoxide (a toxic air pollutant): incomplete combustion of carbon-containing compounds especially fuels.
Sulphur and Nitrogen
Nitrogen dioxide (NO2) and sulphur dioxide (SO2) are major air pollutants.
Sources: Petroleum refineries, combustion of fossil fuels like coal in power plants.
Effects:
Respiratory problems, including permanent lung damage.
Acid rain.
Photochemical smog, which causes breathing difficulties.
Particulate Matter
Particles of solid or liquid that remain suspended in air, water or gas are called particulates.
Example: dust, pollen, debris, soot, acid droplets and smoke.
Causes: Combustion, construction, road dust, power plants, industries, deforestation and agricultural activities.
Effects:
Respiratory and heart diseases.
Asthma
Birth defects
Smog
Smog is made up of smoke and fog.
Types: Classical smog, Photochemical smog
1.Classical smog:
This type of smog occurs in areas with a humid climate and high concentrations of sulphur oxides in the air.
It is a mixture of smoke, fog, and mainly sulphur dioxide gas.
2. Photochemical smog:
This type of smog is prevalent in areas with dry and sunny climate and large numbers of automobiles.
It is formed primarily as a result of chemical interactions among nitrogen oxides and sunlight.
Effects:
Breathing difficulties such as asthma, cough, and wheezing.
Inhibits plant growth and can cause widespread damage to crops and forests.
Photochemical smog leads to the corrosion of metals, building materials, and painted surfaces.
CFCs
Chlorofluorocarbons (CFCs) are compounds of chlorine, fluorine, and carbon.
Uses:
Components of aerosol sprays.
Refrigerants in refrigerators, ACs, and cooling plants.
Effects:
CFCs destruct ozone layer that protects the earth from the sun’s ultraviolet (UV) radiation.
UV exposure can lead to skin cancer, suppression of the immune system and eye damage.
Taj Mahal
Effects of Air Pollution on the Taj Mahal
Carbon dioxide, sulphur dioxide, and nitrogen dioxide react with the water vapour present in the atmosphere to form, carbonic acid, sulphuric acid, and nitric acid respectively.
These acids drop down with rain, making it acidic in nature.
Reactions involved:
CO2(g) + 2H2O(l)→2H2CO3(aq)
2SO2(g) + O2(g) + 2H2O(l)→2H2SO4(aq)
4NO2(g) + O2(g) + 2H2O(l)→4HNO3(aq)
Effects on Taj Mahal:
Acid rain corrodes the marble of the monument.
Air pollution is turning the white marble into the black.
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