TNPSC Environmental Scientist - Atmosphere notes
Atmosphere – Study Notes - TNPSC
Unit I: Introduction to Environment (30 Questions) Environment: Components
– Segments – Atmosphere: Troposphere – Stratosphere – Mesosphere –
Thermosphere – Lithosphere: Crust – Mantle – Core –
Hydrosphere: Fresh water and saline water -
The atmosphere is the gaseous
envelope surrounding the Earth, held in place by gravity. It plays a vital
role in sustaining life, regulating climate, and protecting the planet from
harmful radiation. Without the atmosphere, Earth would be a lifeless, barren
world like the Moon.
Understanding the structure,
composition, functions, and importance of the atmosphere is crucial for
comprehending environmental science, weather, and climate systems.
1.
Composition of the Atmosphere
The atmosphere is made up of a
mixture of gases, water vapor, and dust particles. The composition remains
relatively uniform up to about 80 km from the Earth's surface.
a)
Major Gases:
|
Gas |
Percentage
by Volume |
|
Nitrogen (N₂) |
78.08% |
|
Oxygen (O₂) |
20.95% |
|
Argon (Ar) |
0.93% |
|
Carbon dioxide (CO₂) |
0.04% |
|
Other Gases |
Trace amounts |
b)
Variable Components:
These components vary with time and
location but are vital for weather and life:
- Water vapor: 0–4%
- Ozone (O₃): Protects life by absorbing UV
radiation.
- Dust particles: Help in cloud formation.
- Methane, Nitrous oxide: Greenhouse gases affecting
global warming.
2.
Structure of the Atmosphere (Layers)
The atmosphere is divided into five
main layers based on temperature variations with altitude:
a)
Troposphere (0–12 km)
- Closest layer to Earth’s
surface.
- Contains 75% of the total
mass of the atmosphere.
- Weather phenomena like rain,
clouds, winds, and storms occur here.
- Temperature decreases with
altitude
(about 6.5°C/km).
- Ends at the tropopause,
a boundary layer.
Importance:
- Supports all terrestrial life.
- Contains breathable air.
- Influences climate and weather.
b)
Stratosphere (12–50 km)
- Located above the troposphere.
- Temperature increases with
altitude due
to the presence of the ozone layer.
- Commercial aircraft fly in the
lower stratosphere to avoid turbulence.
- The ozone layer (15–35
km) absorbs harmful ultraviolet (UV) rays.
Importance:
- Filters out harmful UV
radiation.
- Provides stable flying
conditions for aircraft.
c)
Mesosphere (50–80 km)
- Temperature decreases with
height,
reaching the coldest point in the atmosphere (up to -90°C).
- Meteors and shooting stars burn
up in this layer due to atmospheric friction.
- Ends at the mesopause.
Importance:
- Protects Earth from meteoroids.
- Supports the formation of
noctilucent clouds.
d)
Thermosphere (80–700 km)
- Temperature increases
sharply with altitude due to solar radiation absorption.
- Auroras (Northern and Southern
lights)
occur in this layer.
- Contains the ionosphere,
which reflects radio waves and enables long-distance communication.
- Space stations and satellites
orbit here.
Importance:
- Enables radio communication.
- Protects Earth by absorbing
high-energy X-rays and UV radiation.
e)
Exosphere (700–10,000 km)
- Outermost layer where
atmospheric gases gradually fade into space.
- Contains very low-density gases
like hydrogen and helium.
- Satellites orbit in this
region.
Importance:
- Serves as a transition zone
between Earth's atmosphere and outer space.
3.
Functions of the Atmosphere
The atmosphere plays a crucial role
in maintaining conditions necessary for life on Earth.
a)
Protection from Harmful Radiation
- The ozone layer in the
stratosphere absorbs over 97% of UV radiation, protecting skin and
eyes from damage and preventing diseases like skin cancer.
b)
Maintaining Earth’s Temperature (Greenhouse Effect)
- Gases like carbon dioxide,
methane, and water vapor trap heat in the atmosphere, maintaining
the Earth's average temperature at about 15°C.
- Without this effect, Earth
would be frozen at -18°C.
c)
Weather and Climate Regulation
- The movement of air masses,
moisture, and temperature differences drive weather systems.
- Atmosphere distributes solar
heat from the equator to the poles, moderating temperature extremes.
d)
Oxygen for Respiration and Carbon Dioxide for Photosynthesis
- Provides oxygen for
animals and humans to breathe.
- Supplies carbon dioxide
for plants to perform photosynthesis and produce food.
e)
Medium for Sound Propagation
- Sound waves travel through air,
enabling communication.
- In space (a vacuum), sound
cannot travel.
4.
Atmospheric Pressure
- Atmospheric pressure is the weight
of air above a particular point.
- At sea level, standard pressure
is 1013.25 millibars or 1 atmosphere.
- Pressure decreases with
altitude.
- Variations in pressure drive wind
movement and weather patterns.
5.
Winds and Atmospheric Circulation
The unequal heating of the Earth
causes differences in air pressure, which results in wind and global air
circulation.
a)
Types of Winds:
- Planetary Winds: Permanent winds like Trade
Winds, Westerlies, and Polar Easterlies.
- Seasonal Winds: Such as the monsoon winds in
India.
- Local Winds: Land and sea breezes,
mountain and valley breezes.
b)
Jet Streams:
- High-speed winds in the upper
troposphere.
- Influence the development and
movement of weather systems.
6.
Humidity and Precipitation
- Humidity is the amount of water vapor
in the air.
- When air is saturated, precipitation
occurs in the form of rain, snow, sleet, or hail.
- The hydrological cycle
connects the atmosphere to the hydrosphere and biosphere.
7.
Ozone Layer and its Depletion
- Found in the stratosphere,
the ozone layer shields Earth from harmful UV rays.
- Depletion caused by CFCs,
halons, and other ozone-depleting substances (ODS).
- Ozone holes appear especially over
Antarctica during spring.
- Montreal Protocol (1987) – an international treaty to
phase out ODS.
8.
Measures to Protect the Atmosphere
a)
Government Policies:
- Environmental regulations and
air quality monitoring.
- Renewable energy promotion
(solar, wind).
- Emission control standards for
vehicles and industries.
b)
International Agreements:
- Kyoto Protocol (1997) and Paris Agreement (2015)
to limit global warming.
- Montreal Protocol for ozone protection.
c)
Individual Actions:
- Reduce vehicle use, opt for
public transport.
- Save energy at home and switch
to clean energy.
- Avoid burning waste or using
harmful chemicals.
Conclusion
The atmosphere is a crucial
and complex system that supports life on Earth. It not only provides air for
breathing and protection from solar radiation but also plays a central role in
climate and weather regulation.
