Our Environment PDF - 2024-2025

is highly damaging to organisms, for example, it is known to cause skin cancer in human beings. Ozone at the higher levels of the atmosphere is a product of UV radiation acting on oxygen (O2) molecule. The higher energy UV radiations split apart some moleculer oxygen (O2) into free oxygen (O) at...

is highly damaging to organisms, for example, it is known to cause skin cancer in human beings. Ozone at the higher levels of the atmosphere is a product of UV radiation acting on oxygen (O2) molecule. The higher energy UV radiations split apart some moleculer oxygen (O2) into free oxygen (O) atoms. These atoms then combine with the molecular oxygen to form ozone as shown— UV O2  →O+O O + O2 → O3 ( Ozone) The amount of ozone in the atmosphere began to drop sharply in the 1980s. This decrease has been linked to synthetic chemicals like chlorofluorocarbons (CFCs) which are used as refrigerants and in fire extinguishers. In 1987, the United Nations Environment Programme (UNEP) succeeded in forging an agreement to freeze CFC production at 1986 levels. It is now mandatory for all the manufacturing companies to make CFC-free refrigerators throughout the world. Activity 13.4 n Find out from the library, internet or newspaper reports, which chemicals are responsible for the depletion of the ozone layer. n Find out if the regulations put in place to control the emission of these chemicals have succeeded in reducing the damage to the ozone layer. Has the size of the hole in the ozone layer changed in recent years? 13.2.2 Managing the Garbage we Produce In our daily activities, we generate a lot of material that are thrown away. What are some of these waste materials? What happens after we throw them away? Let us perform an activity to find answers to these questions. Activity 13.5 n Collect waste material from your homes. This could include all the waste generated during a day, like kitchen waste (spoilt food, vegetable peels, used tea leaves, milk packets and empty cartons), waste paper, empty medicine bottles/strips/bubble packs, old and torn clothes and broken footwear. n Bury this material in a pit in the school garden or if there is no space available, you can collect the material in an old bucket/ flower pot and cover with at least 15 cm of soil. n Keep this material moist and observe at 15-day intervals. n What are the materials that remain unchanged over long periods of time? n What are the materials which change their form and structure over time? n Of these materials that are changed, which ones change the fastest? Our Environment 213 2024-25