Chapter: Air

• Composition of the Atmosphere

  • Nitrogen (78%)
    • Most abundant gas
    • Helps in plant growth (indirectly via soil bacteria)
  • Oxygen (21%)
    • Second most abundant
    • Essential for survival of humans and animals (respiration)
  • Argon (0.93%)
    • Inert gas
  • Carbon Dioxide (0.03%)
    • Traps heat (greenhouse effect)
    • Essential for photosynthesis in plants
  • Other Gases (0.04%)
    • Helium, ozone, hydrogen, etc.
  • Dust Particles
    • Suspended solid particles in the air

• Structure of the Atmosphere

  • Troposphere
    • Lowest and most important layer
    • Average height: 13 km
    • Contains air we breathe
    • Weather phenomena occur here (rain, fog, storm)
  • Stratosphere
    • Extends up to 50 km height
    • Free from clouds and weather disturbances (ideal for flying aeroplanes)
    • Contains Ozone layer (absorbs harmful UV rays)
  • Mesosphere
    • Extends up to 80 km height
    • Meteorites burn up in this layer on entering from space
  • Thermosphere
    • Rising temperature with height
    • Contains Ionosphere (helps in radio transmission)
    • Extends from 80 to 400 km
  • Exosphere
    • Uppermost layer
    • Very thin air
    • Light gases like helium and hydrogen float into space here

• Weather and Climate

  • Weather
    • Hour-to-hour, day-to-day condition of the atmosphere
    • Can change dramatically within a short time
  • Climate
    • Average weather condition of a place over a long period (e.g., 30 years)

• Major Elements of Weather & Climate

  • Temperature
    • Degree of hotness and coldness of the air
    • Measured in Celsius (°C) or Fahrenheit (°F)
    • Affected by Insolation (incoming solar energy intercepted by earth)
  • Air Pressure
    • Pressure exerted by the weight of air on the earth's surface
    • High pressure: Cold areas, sinking air, clear skies
    • Low pressure: Warm areas, rising air, cloudy skies and wet weather
  • Wind
    • Movement of air from high-pressure area to low-pressure area
    • Types of Winds
      • Permanent Winds (Trade winds, Westerlies, Easterlies)
      • Seasonal Winds (Monsoons - change direction in different seasons)
      • Local Winds (Land/Sea breezes, Loo in India)
  • Moisture (Humidity)
    • Amount of water vapor in the air
    • Precipitation: Falling of moisture in liquid or solid form (Rain, Snow, Sleet, Hail)
    • Types of Rainfall:
      • Convectional Rainfall
      • Orographic (Relief) Rainfall
      • Cyclonic Rainfall