Cbse Class 8 Science Notes Chapter 18

• Pollution is a change in the physical, chemical, or biological features of air, water, or land that can be damaging to human life and other creatures, as well as living circumstances, industrial operations, and cultural assets.

• Pollutants are the agents that cause pollution in our environment. Pollutants are substances that pollute the air, water, or land. For eg. smoke, dust, fog and gases like sulphur dioxide and nitrogen dioxide.

• The contamination of air by contaminants that can harm live creatures and nonliving components is known as air pollution.

• Air Pollution Sources:

1. Sources from nature: Forest fires or volcanic eruptions produce smoke and dust. Methane gas is produced as a result of the decomposition of organic matter.

2. Man-made Exhaust gases from factories, power plants, and autos are among the sources.

The principal air pollutants include carbon monoxide, nitrogen oxides, carbon dioxide, methane, and sulphur dioxide.

Smog is a mixture of smoke and chemicals in the air, along with the fog. Ozone, sulphur dioxide, nitrogen dioxide, and carbon monoxide are some of the chemical components of smog. Smog can exacerbate breathing problems such as asthma and coughing.

• Steps to reduce air pollution include: 

1. Using CNG and unleaded gasoline in autos.

2. Using alternative fuels such as solar, hydropower, and wind energy. 

3. Trees are being planted.

4. Bicycling, taking public transportation or carpooling to school.

5. Keeping leaves, rubbish, and vegetable debris from being burned.

6. Cigarette smoking restrictions.

• Global warming is caused by rising quantities of greenhouse gases such as CO₂ and CFC (Chlorofluorocarbon). Excessive usage of CFCs depletes the ozone layer, which protects the earth from the sun's harmful UV rays.

• Greenhouse Effect and Global Warming: 

The sun's rays warm the earth's surface, causing the greenhouse effect and global warming. The earth absorbs some of the radiation that falls on it and reflects some of it back into space. Because of the presence of greenhouse gases such as water vapour, carbon dioxide, methane, and nitrous oxide, a portion of the reflected radiation gets trapped in the atmosphere. This is referred to as the greenhouse effect.

• The stored radiation warms the globe, even more, causing problems like glaciers melting and rising sea levels. Global warming is the name given to this occurrence.

• Water pollution is defined as the contamination of water by undesirable and harmful things such as sewage, poisonous chemicals, silt, and other contaminants. Some of the biggest impurities of water are sewage, agricultural chemicals, and industrial waste.

• Potable water is water that has been filtered and is safe to drink. Water is an extremely valuable natural resource. It is imperative that we learn to conserve it.

• In 1985, the Ganga Action Strategy, an ambitious plan to save the river, was established. Its goal was to lower the river's pollutant levels. However, the growing population and industrialisation have already irreversibly ruined this majestic river. In 2016, the Indian government established a new project called the National Mission for Clean Ganga (NMCG).

Revision Notes CBSE Class 8 Science Notes Chapter 18 Free PDF Download

What is Pollution?

Environmental pollution can be defined as undesirable changes that happen in the surrounding. These changes have negative and adverse effects on animals, plants, and other physical and biological components of the environment.

Pollutants can either be present in gaseous, solid, or liquid form. A substance can also be classified as being a pollutant when the concentration of that substance is greater than its natural levels. Also, this increase in the concentration of the substance can be caused due to natural or human activities.

Apart from air and water pollution, there are other different types of pollution. The different types of pollution are:

• Light pollution

• Sound pollution

• Soil pollution

Students can learn about these other types of pollutants in other Science Class 8 Chapter Notes.

Understanding Air Pollution

Let’s attempt to understand the Pollution of Air And Water Class 8 Notes by looking at the basics. It is also possible for air to get polluted from natural sources like dust and smoke. This dust and smoke can arise from volcanic eruptions or forest fires. There are also man-made pollutants like power plants, automobile exhaust, and the burning of firewood.

Further, nitrogen oxides, carbon dioxide, methane, carbon monoxide, and sulphur dioxide are major pollutants of the air. It should be noted here that increasing levels of carbon dioxide is one of the major causes of global warming. We will look at the topic of global warming at a later point in these Class 8 Science Ch 18 Notes.

Air pollution can be explained as the introduction of organic molecules, pollutants, and other harmful substances into the atmosphere of the earth. The sources of air pollution can also be classified into two types. These types are:

• Natural (For example, dust storms, forest fire, and volcanic activity)

• Man-made (For example, homes, power plants, industries, transportation, and oil refineries)

There are also Many Effects of Air Pollution. and Some of Those Harmful Effects are:

1. Endangers animal welfare and health of vegetation and plants

2. Results in birth defects in new-born babies

3. Can result in allergies, diseases, and even death to humans

Earlier, we talked about some air pollutants. Now, we will look at all those air pollutants in detail. 

Carbon Monoxide and Carbon Dioxide

Some sources of carbon monoxide are incomplete combustion of carbon-containing compounds, like fuels and other toxic air pollutants. Carbon dioxide, on the other hand, can be produced as a by-product of burning fuels like coal, wood, natural gas, oil, and gasoline. It can also be produced during deforestation and cement production.

Nitrogen and Sulphur

It is important to mention in the notes of Chapter 18 Science Class 8, that both sulphur dioxide (SO₂) and nitrogen dioxide (NO₂) are major pollutants of air. Some sources of sulphur and nitrogen dioxide are the combustion of fossil fuels like coal in power plants and petroleum refineries. There are also various effects of nitrogen and sulphur dioxide, including acid rain, respiratory diseases like permanent lung damage, and photochemical smog-like breathing difficulties.

Particulate Matter

Particulate matter is also an important pollutant that is mentioned in the notes of Chapter 18 Science Class 8. It can be defined as particles of liquid or solid that remain suspended in water, gas, or air. Dust, debris, pollens, smoke, and acid droplets are some examples of particulate matter. Causes of particulate matter are construction, combustion, power plants, road dust, agricultural activities, industries, and deforestation. Particulate matter can cause birth defects, heart diseases, respiratory diseases, and asthma.

Smog

Smog is the combination of fog and smoke. There are different types of smogs. These types of smogs are:

• Photochemical Smog - Photochemical smog is mainly found in areas that have a sunny and dry climate. It is caused due to a large number of automobiles. It is also the result of chemical interactions between sunlight and nitrogen oxides.

• Classical Smog - Classical smog occurs in areas that have a humid climate and high concentrations of sulphur oxides in the air. It is the combination of fog, smoke, and sulphur dioxide gas.

According to Class 8 Pollution of Air and Water Notes, there are many harmful effects of smog. Some of those effects are:

1. It causes issues in plant growth and can also result in widespread damage to forests and crops

2. Breathing problems like cough, asthma, and wheezing

3. It can also cause corrosion of building materials, metals, and painted surfaces

Chlorofluorocarbons (CFCs)

According to Chapter 18 Class 8 Science Notes, CFCs are compounds that are made from fluorine, chlorine, and carbon. CFCs are mainly used as components of aerosol sprays and refrigerants in ACs, refrigerators, and cooling plants.

CFCs harm the ozone layer, which protects the earth from the ultraviolet (UV) radiation from the sun. Because of the increased amount of UV rays, individuals can suffer from diseases like eye damage, skin cancer, and suppression of the immune system.

Another important topic that elaborated in in these NCERT Class 8 Science Ch 18 Notes is the effect of air pollution on the Taj Mahal. There are various components or pollutants in the air that get accumulated in the air. This acid drops down with the rain to make it acidic. The reactions involved in this phenomenon are:

CO₂ (g) + 2H₂O (l) → 2H₂CO₃ (aq)

2SO₂ (g) + O₂ (g) 2H2O (l) → 2H₂SO₄ (aq)

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

This acid rain corrodes the marble of the Taj Mahal. This results in the marble turning from white to black. Many steps have been taken by the government to solve this problem and protect the marble of the Taj Mahal.         

What is Global Warming?

According to experts, global warming can be defined as a phenomenon in which gases that are responsible for the greenhouse effect, accumulate and trap more heat. Greenhouse gases capture a percentage of the sun’s radiation to maintain the temperature on the earth in a phenomenon known as the greenhouse effect.

This is different because most of the solar radiations that are passing through the atmosphere should bounce back into space. But due to the excess of greenhouse gasses, these radiations get trapped in the atmosphere. This makes the earth hotter than it should be.

In other words, it can be said that if greenhouse gases are trapping an appropriate amount of heat, then that is called the greenhouse effect. But if there are more greenhouse gases and more heat is being trapped than necessary, then that is called global warming.

Readers should also know what greenhouse gases are. The greenhouse gases mainly are - carbon dioxide, nitrous oxide, water vapes, and methane. We also know that global warming has many negative effects on the earth. But what are those effects? If you want to learn about those effects, then you should go through the list that is mentioned below.

• Global warming has resulted in an increase in the average temperature of our planet

• There has also been an increase in the severity and occurrence of natural disasters like cyclones, floods, and earthquakes

• Climate patterns have shifted dramatically all across the globe

• There has also been a rise in the average sea levels all across the globe. This is happening because the polar ice caps are melting

All of These Effects are Drastic and Can Even Destroy Life on Earth. So, What Can We Do?

It is recommended that everyone should try to protect the environment as much as possible. There are some steps that can be practised at an individual level. Some of those measures are:

• Use cleaner fuels as compared to diesel and petrol

• Use unleaded petrol. This is because unleaded petrol does not emit harmful gases into the environment

• Waste should be properly managed. It should not be left in the open. Instead, waste should be incinerated or disposed of in a safe manner

• You should try to carpool or use public transport because it is economical, prevents congestion on roads, and also reduces the emission of harmful gases to a large extent

What is Water Pollution?

Water pollution can be defined as the contamination of water bodies because of harmful waste. It can be caused due to industries, urbanization, social practices, religious practices, and agriculture.

In recent years, the biggest example of water pollution has been the river Ganga. The river Ganga has been polluted by many water pollutants like insecticides, hospitals, chemicals, detergents, and herbicides.

Apart from the river Ganga, there are many rivers that are filled with nothing but garbage, untreated sewage, and dead bodies of animals. All of this is choking aquatic life and hindering the growth of plants inside water bodies. According to various sources, Ganga is one of the ten most endangered rivers in the world. 

Water Can Be Broadly Classified As

• Potable Water: It is the water that is suitable for drinking. It is free from all harmful bacterias and contaminants

• Raw Water: It is the water that is not potable or fit for drinking

Converting Raw Water to Potable Water

• It is possible to kill all the bacteria and microbes in water by boiling water. Boiling water also protects individuals against various waterborne diseases. Filtering water can also work. It is the process that separates suspended solid matter from a liquid. However, this method will only work to a certain extent.

• Chlorination is another process that can help in cleaning water. This process is done by adding chlorine tablets or bleaching powder to the water. This method kills various bacterias and microbes that are present in tap water.

Chlorination is a more complex procedure than you might have understood from this description. This is why we have attached an image below. This image showcases the process of chlorination. It is suggested that readers should go through this image carefully to understand chlorination in a better manner.

(Image to be added soon)

With all being said, one question that still remains unanswered is how crucial are water and air. We have answered this question in the list that is mentioned below.

Importance of Air

• Air is an inevitable part of our lives

• It helps in producing energy in our bodies

• It is vital for the survival of the animals and plants

Importance of Water

• It plays a vital role in sustaining life on earth

• Water helps in carrying out various human activities like drinking, agriculture, cleaning, and washing

Fun Facts about Pollution

Did you know that pollution is one of the biggest killers in the world? According to official sources, pollution affects over 100 million people all across the globe every single year! These numbers are comparable to the statistics of global diseases like HIV and malaria.

According to a study carried out by the National Academy of Sciences in 1975, industries have dumped almost 14 billion pounds of garbage into the oceans. Also, because of pollution, almost 1 million seabirds and 100,000 sea mammals are killed due to pollution every single year. Further, if you live in places with high levels of air pollutants, then you are at a 20% higher risk of dying from lung cancer in comparison to other people who live in less polluted areas.

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