CBSE Class 8 Science Revision Notes Chapter 18

Class 8 Science Revision Notes Chapter 18

CBSE Class 8 Science Revision Notes Chapter 18 – Pollution of Air and Water 

In recent years, our surroundings have drastically changed. Pollution is one of the major factors why that has happened. This is what the Class 8 Science Chapter 18 Notes discuss. The important topics of the chapter include pollution, pollutants, types of pollution, global warming, etc.

Students are advised to create chapter-wise notes before their exams for better preparation. Extramarks’ revision notes curated by the subject experts will save time and help to ease their preparation process. They can strengthen their concepts by referring to these notes that are prepared according to the recent CBSE Syllabus. 

Extramarks is a platform that provides NCERT solutions, notes, and other study material for students. These notes are easily accessible from the website and help with well-rounded preparation to score better marks in the exams.

Revision Notes for CBSE Class 8 Science Chapter 18

Access Class 7 Science Chapter 18 – Pollution of Air and Water 

Revision Notes CBSE Class 8 Science Notes Chapter 18

What is Pollution?

Undesirable changes to the environment are referred to as environmental pollution. Animals, plants, and other physical and biological elements of the ecosystem are negatively and adversely impacted by these changes.

Pollutants may exist in the form of a gas, a solid, or a liquid. When a substance is present in greater concentrations than it does naturally, it can also be categorised as pollution. The concentration of the substance may also grow as a result of human or natural activity.

Pollutants are the causes of environmental contamination. Pollutants are substances that harm the air, the water, or the land. For example, nitrogen dioxide and sulphur dioxide gases, dust, smoke, and smog.

Students can learn about these types of pollutants in detail in Chapter 18 Science Class 8 Notes provided by Extramarks.

Apart from water and air pollution, there are also other types of pollution. The other types of pollution are as follows:

• Soil pollution
• Light pollution
• Sound pollution

Understanding Air Pollution

Students will understand air pollution through the related concepts described in Class 8 Science Notes Chapter 18. Dust and smoke are examples of natural pollutants that can affect the quality of the air. Both forest fires and volcanic eruptions may produce this dust and smoke. In addition, there are man-made air pollutants such as those produced by power plants, car emissions, and firewood burning.

Significant air pollutants include methane, carbon monoxide, carbon dioxide, nitrogen oxides, and sulphur dioxide. It should be emphasised that growing carbon dioxide levels are one of the primary causes of global warming. Class 8 Chapter 18 Science Notes also explains global warming.

Air pollution can be caused by the release of organic molecules, contaminants, and other harmful substances into the earth’s atmosphere. The following are some of the main causes of air pollution:

• A forest fire’s ash and smoke
• The carbon monoxide that is created while burning gasoline and diesel
• Burning of wood
• An automobile’s exhaust
• The smog produced by manufacturing

These air pollution sources can be divided into two categories. These kinds include:

• Natural (For instance, forest fire, dust storms, and volcanic activity)
• Man-made (For instance, power plants, homes, transportation, industries, and oil refineries)

The effects of air pollution are numerous as well and a few of those negative effects include:

• Threatens the health of plants and vegetation as well as animal wellbeing
• Causes birth abnormalities in newborns
• May cause allergies, infections, or even human death

Carbon Monoxide and Carbon Dioxide 

The incomplete combustion of carbon-containing compounds, such as fuels and other dangerous air pollutants, is one source of carbon monoxide. On the other hand, burning fuels like coal, wood, natural gas, oil, and gasoline can result in the production of carbon dioxide. It can also be created during the production of cement and deforestation.

Nitrogen and Sulphur 

Nitrogen dioxide (NO2) and sulphur dioxide (SO2) are significant air pollutants. The burning of fossil fuels like coal in power plants and petroleum refineries is one source of sulphur and nitrogen dioxide. Additionally, nitrogen and sulphur dioxide have several impacts, such as acid rain, respiratory conditions such as lifelong lung damage, and breathing issues similar to photochemical smog. All these things are discussed in detail in the notes provided.

Particulate Matter 

Another significant pollutant is particulate matter. It is characterised as liquid or solid particles that float freely in liquid, gas, or air. Particulate matter includes things like dust, debris, pollen, smoke, and acid drops. Construction, combustion, power plants, road dust, agricultural activities, industry, and deforestation are some of the factors that contribute to particulate matter. Asthma, heart disease, respiratory conditions, and birth defects are some of the negative effects of increased particulate matter.

Smog

Smog is the combination of fog and smoke. These smog come in the following varieties:

• Photochemical Smog: In regions with a hot, dry climate, photochemical smog is more common. It is brought on by the excessive quantity of vehicles. The chemical reactions between sunlight and nitrogen oxides also contribute to it.
• Classical Smog – Classical smog happens in places with a humid environment and lots of sulphate-containing air pollutants. It is a mixture of sulphur dioxide gas, smoke, and fog.

The Class 8 Pollution of Air and Water Notes describe a number of negative effects of smog. Among those results are:

• It hinders plant growth and has the potential to seriously harm forests and agriculture.
• It can cause breathing issues such as asthma, coughing, and wheezing.
• Additionally, it may cause painted surfaces, metals, and building materials to corrode.

Chlorofluorocarbons (CFCs)

Chlorofluorocarbons (CFCs) are compounds that are made from carbon, fluorine, and chlorine. CFCs are mostly utilised as refrigerants in air conditioners, refrigerators, and cooling plants as well as in aerosol sprays.

The ozone layer, which shields the earth from ultraviolet (UV) radiation from the sun, is harmed by CFCs. People are more likely to develop ailments like eye damage, skin cancer, and immune system suppression as a result of increased exposure to UV rays.

The impact of air pollution on the Taj Mahal is a major topic that is covered in these NCERT Class 8 Science Chapter 18 Notes. The air contains a variety of substances or pollutants that build up over time. It becomes acidic and this acid is washed down with rain. In this process, there are the following reactions:

CO₂ (g) + 2H₂O (l) → 2H₂CO₃ (aq)

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

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

The Taj Mahal’s marble deteriorates because of this acid rain. As a result, the marble changes from white to black. Initiatives have been taken by the government to address this issue and protect the marble of the Taj Mahal.

What is global warming?

The phenomenon of extra heat being trapped by gases that are responsible for the greenhouse effect is known as global warming. The greenhouse effect is a process whereby greenhouse gases absorb a portion of solar energy to keep the earth’s temperature constant.

This is different because the majority of solar radiation should be reflected back into space that passes through the atmosphere. However, these radiations become trapped in the atmosphere as a result of the overproduction of greenhouse gases. As a result, the earth becomes warmer than it should be.

In other words, it can be stated that the greenhouse effect occurs when greenhouse gases trap an adequate quantity of heat. Global warming, however, refers to the situation when there are more greenhouse gases and more heat is trapped than is necessary.

It is also important to understand what greenhouse gases are. Carbon dioxide, nitrous oxide, water vapour, and methane are the main greenhouse gases. It is known that the globe is negatively impacted by global warming in numerous ways. The following list discusses some of these consequences:

• The planet’s average temperature has increased as a result of global warming.
• Natural disasters including earthquakes, floods, and cyclones have also become more frequent and severe.
• Globally, climate patterns have undergone a significant change.
• Additionally, average sea levels have increased throughout the world. This is due to the melting of the polar ice caps.

All of these effects are severe and have the potential to endanger life. Therefore, it is advised that everyone should make an effort to preserve the environment as much as they can. Various steps can be taken on an individual basis such as:

• Use cleaner fuels instead of diesel and gasoline.
• Utilise unleaded petrol. This is because unleaded petrol doesn’t release hazardous gases into the atmosphere.
• Waste should be handled carefully. It shouldn’t be exposed to the open. Instead, garbage should be handled or disposed of safely.

• Try to carpool or utilise public transport as it is economical, reduces the emission of harmful gases to a large extent, thereby leading to less pollution and also prevents congestion on roads.