Chapter 4 — Air

The atmosphere is a huge blanket of air surrounding the earth, composed mainly of nitrogen and oxygen, divided into five layers — Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere — and essential for all weather, climate, and life on earth.

The atmosphere is Earth's blanket of air, made mainly of nitrogen (most plentiful) and oxygen (second most plentiful), with smaller amounts of carbon dioxide, helium, ozone, argon, and hydrogen. It is divided into five layers: Troposphere (average 13 km, where all weather occurs), Stratosphere (up to 50 km, contains the ozone layer, ideal for aircraft), Mesosphere (up to 80 km, where meteorites burn up), Thermosphere (80–400 km, where radio waves are reflected), and Exosphere (outermost, very thin air). Carbon dioxide creates the greenhouse effect; excess CO2 from burning fuels causes global warming. Weather is the hour-to-hour atmospheric condition; climate is the long-term average. Temperature is influenced by insolation, which decreases from the equator to the poles. Air pressure is highest at sea level and decreases with height. Wind — movement from high to low pressure areas — is classified as permanent, seasonal, or local. Moisture in air leads to humidity, clouds, and three types of rainfall: convectional, orographic, and cyclonic.

1. 01Nitrogen is the most plentiful gas in the atmosphere; plants cannot absorb it directly — soil bacteria convert it into a usable form.
2. 02The atmosphere has five layers: Troposphere (13 km average, all weather here), Stratosphere (up to 50 km, ozone layer, best for aircraft), Mesosphere (up to 80 km, meteorites burn here), Thermosphere (80–400 km, radio waves reflect here), and Exosphere (outermost, very thin).
3. 03Carbon dioxide creates the greenhouse effect by trapping heat; rising CO2 from burning fuels causes global warming, which melts polar ice and raises sea levels, causing coastal floods.
4. 04Insolation (incoming solar energy intercepted by the earth) decreases from the equator towards the poles, explaining why temperature falls the same way and poles remain snow-covered.
5. 05Air pressure is highest at sea level and decreases with height; high temperature creates low pressure (cloudy, wet weather) and low temperature creates high pressure (clear, sunny skies).
6. 06Winds are classified as permanent (trade winds, westerlies, easterlies), seasonal (e.g., monsoons in India), and local (e.g., loo in northern India, land and sea breeze).
7. 07Rainfall occurs in three forms — convectional, orographic (relief), and cyclonic; other forms of precipitation include snow, sleet, and hail.
8. 08The 1999 Odisha supercyclone had winds up to 260 km per hour lasting over 36 hours, tidal waves 7–10 m high, and affected about 13 million people.