Our Impact on the Environment: Quick Revision

A brief note on Our Impact on the Environment. Read it before a test. Try each question at the end before you open its answer.

The ozone layer

• Ozone is $\mathrm{O_3}$: three oxygen atoms. Near the ground it is a poison.
• High in the atmosphere it forms the ozone layer, which absorbs most of the Sun's UV radiation.
• UV can cause skin cancer and harm the eyes and the body's defences.
• It forms in two steps: $\mathrm{O_2} \to \mathrm{O} + \mathrm{O}$ under UV, then $\mathrm{O} + \mathrm{O_2} \to \mathrm{O_3}$.
• CFCs from refrigerants and fire extinguishers thinned the layer.
• In 1987 a UNEP agreement froze CFC production at 1986 levels.

Two kinds of waste

• Biodegradable: broken down by decomposers. Peels, food, paper, cotton, leaves.
• Non-biodegradable: not broken down. Plastic, glass, metal cans, some pesticides.
• Decomposers' enzymes act only on certain substances, so plastics last for centuries.
• Plastic blocks drains, harms animals that eat it, and fills landfills.

Managing garbage

• Reduce, reuse, recycle, in that order.
• Green bin: wet waste, for compost. Blue bin: dry waste, for recycling.
• Burning garbage releases harmful gases.
• Every choice has a cost: kulhads use up fertile topsoil.

A worked example

A family's weekly waste is $5$ kg of wet waste and $3$ kg of dry waste. About $40$ % of the wet waste remains as compost. What is the wet share, and how much compost is made?

1. All the waste. $5 + 3 = 8$ kg.
2. Wet share. $\dfrac{5}{8} \times 100 = 62.5$ %.
3. Compost. $5 \times \dfrac{40}{100} = 2$ kg.

Practice with new numbers

A program to try

The program finds a family's garbage in a month.

Mistakes to avoid

• Not all ozone is good. Near the ground it is a poison.
• CFCs, not carbon dioxide, thinned the ozone layer.
• Paper is biodegradable, though it goes in the dry bin for recycling.
• Reduce comes before recycle.
• Kulhads are not free of cost: they use up topsoil.

Check yourself

1. What is the chemical formula of ozone?

2. Which chemicals were the main cause of the thinning of the ozone layer?

3. Name one biodegradable and one non-biodegradable item from a kitchen.

4. A family makes $7$ kg of wet waste and $3$ kg of dry waste in a week. What percentage is wet?

5. Why is reducing better than recycling?