Q.What do you understand by ozone layer depletion? Describe how depletion of ozone layer occurs in the stratosphere. ($1+2=3$)

Think of the ozone layer as a very thin, invisible sunscreen wrapped around the Earth, floating roughly 15 to 35 kilometres above your head. You don't see it, you don't feel it, but it is doing a brutal, thankless job every second of every day: it absorbs most of the Sun's ultraviolet radiation, the part of sunlight that would otherwise cook your skin, damage your eyes, and wreck crops. Without it, life on land as we know it would be impossible. So when we talk about ozone layer depletion, we are talking about a tear in that sunscreen — a thinning of the shield that lets more of that dangerous radiation through to the ground.

The story starts with a class of chemicals called chlorofluorocarbons, or CFCs. These were invented in the 1920s and were considered miracle substances: they were cheap, non-flammable, and stable. They went into refrigerators, air conditioners, aerosol spray cans, and foam packaging. The problem is that "stable" is a double-edged sword. A CFC molecule released at ground level does not break down easily; it just floats up, unchanged, for years. When it finally reaches the stratosphere, the intense ultraviolet light there smashes it apart, releasing a chlorine atom. And that single chlorine atom is a tiny, relentless predator. It attacks an ozone molecule, steals an oxygen atom from it, and in the process destroys the ozone. The chlorine atom is then free to do it again, and again, and again — one chlorine atom can destroy tens of thousands of ozone molecules before it is finally removed. That is the core mechanism: a stable chemical, harmless at ground level, becomes a serial killer of ozone once it reaches the upper atmosphere.

Why should a commerce or humanities student care? Because this is not just a chemistry story; it is a story about markets, regulation, and collective action. The damage was not caused by a few careless factories — it was caused by a global industry that produced billions of dollars of goods. The fix was not a technological miracle; it was a political and economic agreement. In 1987, the world's governments signed the Montreal Protocol, an international treaty that phased out the production of CFCs. It is widely considered the most successful environmental treaty in history, precisely because it worked: the ozone layer is slowly healing, and scientists expect it to recover by the middle of this century. The lesson here is that human-made problems, even ones that seem purely scientific, are solved through negotiation, economics, and law — the very stuff of your field.

Here is what the depletion actually does to us, in plain terms:

• Health: More UV-B radiation reaching the ground means more skin cancers, more cataracts, and a weaker immune system in humans.
• Agriculture: UV radiation damages crops and reduces yields, which hits food supply and farmers' incomes.
• Marine life: It harms phytoplankton, the tiny organisms at the base of the ocean food web, which would ripple through the entire fishing industry. …