Atmosphere Chapter Notes | Earth and Environmental Science for Year 11 PDF Download

​Introduction

The Earth's atmosphere is a vital layer of gases that surrounds our planet, making life possible by providing essential elements like oxygen, protecting us from harmful solar radiation, and maintaining a suitable temperature. This chapter explores the composition, structure, and importance of the atmosphere, along with its role in processes like the greenhouse effect, global warming, and ozone depletion. It also discusses how human activities impact the atmosphere and what we can do to reduce negative effects.

Atmosphere

• A layer of gases surrounding the Earth, extending up to 1,000 km from the surface.
• Held in place by Earth's gravity.
• Along with liquid water, makes Earth unique in the solar system.
• Protects from harmful solar radiation and burns up meteoroids.
• Contains the ozone layer to filter ultraviolet rays.
• Provides oxygen for living organisms to breathe.

Composition of the Atmosphere

• Consists of gases, water vapor, and dust particles.
• Composition varies with time and place.
• Nitrogen and oxygen make up 99% of the atmosphere.
• Other gases include argon, carbon dioxide, hydrogen, neon, and helium.

Nitrogen

• Most abundant gas in the atmosphere.
• Colorless and odorless.
• Essential for the growth of living organisms.

Oxygen

• Important gas used by plants and algae in photosynthesis.
• Photosynthesis uses carbon dioxide, water, and sunlight to produce oxygen and glucose.
• Oxygen is used by living organisms for respiration.

Carbon Dioxide

• Produced during respiration by living organisms.
• Used by plants and microorganisms in photosynthesis to make food.
• Contributes to the greenhouse effect, which helps maintain Earth's temperature.

Main sources include:

• Volcanic eruptions.
• Respiration of living organisms.
• Decay of dead organisms.
• Burning of fossil fuels.
• Land cultivation.

Water Vapour

• Gaseous form of water in the atmosphere.
• Plays a key role in cloud formation and precipitation.
• More abundant in hot and wet regions, less in dry regions.
• Affects weather, causing fog in winter mornings and humid conditions in coastal areas during summer.
• Generated through evaporation from water bodies and transpiration from plants.

Ozone

• Found in small amounts in the ozone layer.
• Absorbs harmful ultraviolet rays from the sun.
• Protects living beings from harmful radiation.

Argon

• An inert gas that does not react with other substances.
• Has a full outer electron shell, making it chemically stable.

Dust Particles

• Present as sand, smoke, and oceanic salt.
• Help in condensing water vapor to form clouds and precipitation.
• Reflect sunlight and contribute to the colors seen during sunrise and sunset.

Structure of the Atmosphere

• Divided into five layers based on temperature and altitude.
• Layers are arranged like spherical shells around the Earth.

Troposphere

• Lowest layer, containing 70% of the atmosphere's mass.
• Extends 18 km at the equator and 8 km at the poles.
• Wider at the equator due to strong convection currents.
• Contains dust particles and water vapor.
• Where all weather changes occur, also called the "changing sphere."
• Separated from the stratosphere by the tropopause.
• Tropopause temperature is about -80°C at the equator and -45°C at the poles.

Stratosphere

• Located above the troposphere, up to 50 km high.
• Temperature remains constant up to 20 km, then increases due to ozone.
• No weather changes; air moves horizontally, ideal for aircraft.
• Contains the ozone layer (20–30 km), measured in Dobson Units.
• Ozone layer filters ultraviolet rays, protecting life from sunburn.
• Upper limit is the stratopause.

Mesosphere

• Third layer, extending up to 80 km.
• Temperature decreases with altitude, reaching -100°C at 80 km.
• Meteors burn up in this layer, protecting Earth.
• Upper limit is the mesopause.

Thermosphere (Ionosphere)

• Extends from 80 km to 500 km.
• Contains charged particles (ions), reflecting radio waves for broadcasting.
• Temperature increases with height due to solar radiation absorption.
• Protects Earth by burning up meteors and debris.
• Divided into sublayers for transmitting different radio wave frequencies.

Exosphere

• Uppermost layer, from 500 km to 10,000 km.
• Very low air density due to weak gravity.
• Dominated by hydrogen and helium gases.
• Merges gradually into outer space.

Greenhouse Effect and Global Warming

• The Earth is surrounded by a layer of air called the atmosphere, acting like a blanket.
• This helps maintain a comfortable temperature of about 15°C on Earth.
• The greenhouse effect allows sunlight to enter during the day, but some heat is trapped by greenhouse gases.
• Some heat is absorbed by the Earth's surface, and some is reflected back to Earth by these gases.
• This process is known as the greenhouse effect, essential for keeping Earth warm.
• Without the greenhouse effect, Earth would be too cold and likely uninhabitable.

Greenhouse gases include:

• Water vapor.
• Carbon dioxide.
• Methane.
• Nitrous oxide.
• Ozone.
• Chlorofluorocarbons (CFCs).
• Greenhouse gases occur naturally and are harmless when balanced.
• Too much of these gases causes an imbalance, leading to global warming.
• Global warming is the process where Earth's average temperature increases beyond the normal level.

Causes of Global Warming

Carbon Dioxide

• Main contributor to global warming.

Human sources include:

• Burning fossil fuels (coal, oil, wood) for energy or domestic use.
• Deforestation, releasing stored carbon as carbon dioxide.
• Land use changes, like clearing forests for buildings or biofuel production.

Methane

• Second major contributor, 21 times more harmful than carbon dioxide.
• Produced by decomposing organic matter and digestion in ruminants.

Human sources include:

• Decomposing organic matter in landfills, animal waste, sewage, and dams, where bacteria produce methane that escapes into the atmosphere.
• Natural gas extraction, such as fracking, where methane is released during oil and gas operations.

Nitrous Oxide

• Released from soil cultivation using organic pesticides and fertilizers.
• Levels have increased by 18% since the Industrial Revolution.

Chlorofluorocarbons (CFCs)

• Long-lasting greenhouse gases that also harm the ozone layer.
• Do not occur naturally; they are man-made compounds used in aerosols, refrigerants, and other industrial products.
• Along with carbon dioxide, CFCs create a thick layer in the atmosphere that traps the sun's rays.
• Continued use of oil and coal increases the amount of these harmful gases in the atmosphere.

Impact of Global Warming

Desertification

• Rising temperatures disrupt the water cycle and rainfall patterns.
• Arid and semi-arid areas become drier, affecting over 2.5 million people.

Increased Melting of Snow and Ice

• Snow and ice melt faster in regions like the Alps, Himalayas, and poles.
• Arctic ice melts at 11.5% per decade; thickness reduced by 48% since the 1960s.
• Antarctica loses over 100 cubic km of ice annually since 2002, doubling since 2010.

Rising Sea Levels

• Sea levels have risen 21 cm since 1880 due to thermal expansion and melting ice.
• Threatens to submerge islands and coastal areas.

Loss of Biodiversity

• Species may need to migrate to higher altitudes or latitudes due to temperature changes.
• Many species, like polar bears, face extinction risks.

Ways to Reduce Global Warming

• Global warming affects the Earth daily, but we can help reduce it in simple ways.
• Reducing the carbon dioxide we produce, also called our carbon footprint, can make a big difference.
• Coral reefs are suffering from global warming and pollution, with the highest death rate since 1980.

Here are some ways to help:

• Carpooling with friends or co-workers: Cars release a lot of carbon dioxide when burning fuel. Sharing rides reduces the number of cars on the road, lowering emissions and saving fuel costs.
• Replace plastic water bottles with reusable ones: Plastic bottles create a lot of waste, and many are not recyclable. Using reusable bottles reduces trash and lowers carbon dioxide and methane in the atmosphere.
• Recycle and reuse: Sorting items for recycling keeps landfills less full, reducing your carbon footprint over time.
• Plant trees at home: If you have space, planting trees cools your surroundings in summer and absorbs carbon dioxide from the air.

Ozone Depletion

• Reduction of ozone in the stratosphere, increasing exposure to ultraviolet rays.
• Caused by substances like CFCs, halons, methyl chloroform, carbon tetrachloride, HCFCs, and methyl bromide.
• Found in refrigerators, air conditioners, fire extinguishers, aerosols, and solvents.
• These substances release chlorine atoms in the stratosphere, breaking down ozone.
• Notable thinning occurs over Antarctica, known as the "ozone hole."

Effects of Ozone Depletion

Damage to Human Health

• If the ozone layer depletes, humans are directly exposed to strong ultraviolet (UV) rays.
• Too much UV exposure can cause skin cancer, cataracts, sunburn, a weaker immune system, and faster aging.

Devastation to Environment

• Many crops are harmed by strong UV rays, leading to reduced growth, photosynthesis, and flowering.
• Crops like barley, wheat, corn, oats, rice, broccoli, tomatoes, and cauliflower are affected.
• Forests also suffer from the effects of ozone depletion.

Threat to Marine Life

• Strong UV rays can harm marine life, especially planktons, which are key in the aquatic food chain.
• A decrease in planktons due to ozone depletion can disrupt the marine food chain.

Effect on Animals
Excessive UV exposure can cause skin cancer and eye cancer in animals.

Impact on Certain Materials
Materials like plastics, wood, fabrics, and rubber get heavily damaged when exposed to ultraviolet rays.

Solutions to Ozone Depletion

• Pesticides are useful for farms but harm the ozone layer; using natural methods to control pests can help.
• Reducing the number of vehicles on the road can lower emissions that form smog, which contributes to ozone depletion.
• Homes often use harsh chemicals that harm the ozone layer; using eco-friendly cleaning products can reduce this impact.
• The Montreal Protocol of 1989 helped limit CFCs, but it did not cover nitrous oxide, a harmful chemical still in use.
• Governments should ban nitrous oxide to further reduce the rate of ozone layer depletion.

Points To Remember

• Atmosphere is a gaseous layer surrounding the Earth.
• Nitrogen and oxygen form 99% of the atmosphere.
• Atmosphere has five layers: troposphere, stratosphere, mesosphere, thermosphere (ionosphere), and exosphere.
• Ionosphere reflects radio waves, enabling broadcasting.
• Carbon exists as carbon dioxide in the atmosphere.
• Oxygen is essential for respiration and fuel combustion.
• Global warming increases Earth’s average temperature.
• Greenhouse gases trap heat, contributing to the greenhouse effect.
• Ozone depletion reduces stratospheric ozone, increasing UV exposure.