Pollution Of Air And Water Class 8 Notes

Key Points to Remember

• Pollution is the contamination of natural resources by harmful substances, making them unfit for use.
• Air pollutants include suspended particulate matter (SPM), carbon monoxide, sulphur dioxide, nitrogen oxides, and chlorofluorocarbons (CFCs).
• The Greenhouse Effect is a natural process where certain atmospheric gases (like CO2, CH4) trap heat, warming the Earth. Excessive greenhouse gases lead to Global Warming.
• Acid Rain occurs when sulphur dioxide and nitrogen oxides react with water vapour to form acids, falling back to Earth.
• Water pollutants include sewage, industrial waste, agricultural chemicals (pesticides, fertilizers), and garbage.
• Potable water is water that is safe for drinking.
• Eutrophication is the excessive growth of algae due to nutrient enrichment (e.g., from agricultural runoff) in water bodies, depleting oxygen and harming aquatic life.
• The 3Rs (Reduce, Reuse, Recycle) are crucial for minimizing waste and pollution.
• Water purification methods include filtration, chlorination, and boiling.

Key Definitions

Pollution

The addition of unwanted or harmful substances into the environment, causing adverse effects on living organisms and the environment.

Pollutants

Substances that contaminate the environment.

Air Pollution

Contamination of air by harmful gases, dust, and smoke, which affects the health of living beings and damages non-living things.

Global Warming

A gradual increase in the Earth's average surface temperature due to the accumulation of greenhouse gases in the atmosphere.

Acid Rain

Rain or any other form of precipitation that is unusually acidic, meaning that it possesses elevated levels of hydrogen ions (low pH). It is caused by emissions of sulfur dioxide and nitrogen oxide.

Water Pollution

The contamination of water bodies, usually as a result of human activities, in such a manner that its quality is reduced and it becomes harmful to living organisms.

Potable Water

Water that is safe to drink and prepare food with.

Eutrophication

The process of nutrient enrichment in a water body, primarily by nitrates and phosphates, leading to excessive growth of algae and other aquatic plants, and subsequent oxygen depletion.

Chlorination

A process of disinfecting water by adding chlorine to kill harmful microorganisms.

The Greenhouse Effect and Global Warming

The Greenhouse Effect is a natural phenomenon essential for life on Earth. It occurs when certain gases in the Earth's atmosphere, known as greenhouse gases, trap heat from the sun. Without this effect, the Earth's surface would be too cold to support most life forms. Key greenhouse gases include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and water vapour.

Sunlight (shortwave radiation) passes through the atmosphere and warms the Earth's surface. The Earth then radiates some of this energy back into space as infrared radiation (longwave radiation). Greenhouse gases absorb some of this outgoing infrared radiation, preventing it from escaping directly into space, and re-radiate it back towards the Earth, effectively trapping heat. This process maintains a habitable temperature on our planet.

However, human activities, primarily the burning of fossil fuels (coal, oil, natural gas) for energy, industrial processes, and transportation, have significantly increased the concentration of these greenhouse gases in the atmosphere. Deforestation also contributes to this by reducing the number of trees that absorb CO2. The enhanced Greenhouse Effect, caused by this excess accumulation of greenhouse gases, leads to an abnormal rise in the Earth's average surface temperature, a phenomenon known as Global Warming.

Consequences of Global Warming are severe and include: melting of glaciers and polar ice caps, leading to a rise in sea levels; changes in precipitation patterns, causing more frequent floods and droughts; increased intensity of extreme weather events; and disruptions to ecosystems and agriculture. Mitigating global warming requires global efforts to reduce greenhouse gas emissions and promote sustainable practices.

Air Pollution vs. Water Pollution

The Process of Water Purification at Home

1. — Use a water filter (mechanical filters, activated carbon filters) to remove suspended impurities, sediments, and some chemicals. Boiling also removes larger impurities.
2. — Heating water to a rolling boil for at least 1 minute effectively kills most bacteria, viruses, and other pathogens present in the water.
3. — After boiling, or as an alternative, add chlorine tablets or a few drops of household bleach (containing hypochlorite) to disinfect the water. Allow sufficient contact time as per instructions. Be cautious with dosage.
4. — Advanced purifiers use RO membranes to remove dissolved salts, heavy metals, and microorganisms, or UV light to inactivate pathogens without adding chemicals. These are common in modern household systems.

Exam Tip: Diagrams & Examples

When answering questions about pollution, especially its causes, effects, and control, always try to include specific examples. For instance, instead of just saying "industrial waste," mention "untreated chemical discharge from factories." For effects, state "respiratory illnesses like asthma" for air pollution or "cholera and typhoid" for water pollution. If asked to describe the Greenhouse Effect, a simple labelled diagram can fetch you extra marks and clearly demonstrate your understanding. Practice drawing flowcharts for processes like acid rain formation or eutrophication. Remember the 3Rs (Reduce, Reuse, Recycle) as a universal solution for most environmental problems.

Practice Questions with Solutions

• Q: Name any two greenhouse gases. A: Carbon dioxide (CO2) and Methane (CH4).
• Q: What is acid rain and how is it caused? A: Acid rain is precipitation with unusually high acidity, caused by sulfur dioxide and nitrogen oxides reacting with water vapour in the atmosphere.
• Q: What is potable water? A: Potable water is water that is safe for drinking and cooking.
• Q: List two effects of water pollution on aquatic life. A: Harm to aquatic organisms and depletion of oxygen due to eutrophication.

Frequently Asked Questions