Question
Our atmosphere acts as a greenhouse. Explain.
✓
Answer
Our atmosphere contains greenhouse gases such as $CO _2$, water vapour, $O _3, CH _4$, oxides of nitrogen and CFCs and allows the sun rays to come in. Sunlight reaching the Earth consists of three types of radiation-UV radiation, visible radiation, and IR radiation. As sunlight passes through the atmosphere, most UV radiation is absorbed by ozone; $30 \%$ of IR radiation reaches the Earth's surface, heating it up. As the Earth's surface becomes hot, it starts emitting radiation with less energy than the incoming radiation and thus with a longer wavelength. Some emitted IR radiation escapes from the Earth's surface and some is absorbed by $CO _2$, thus remaining on the Earth. Trapped radiation warms the Earth's surface and lower layers of the atmosphere.
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