Variable Component:Water Vapor (H₂O), which can range from 0% to 4% and is responsible for clouds and weather.
Importance of Atmosphere
Provides Gases for Life: It contains the oxygen (O₂) we breathe and the carbon dioxide (CO₂) plants use for photosynthesis.
Filters Harmful Radiation: The ozone layer in the stratosphere blocks most of the sun's harmful ultraviolet (UV-B and UV-C) radiation.
Regulates Temperature (Greenhouse Effect): It traps heat from the sun, keeping the planet warm enough for life to exist. Without it, Earth's average temperature would be about -18°C.
Weather and Water Cycle: It is the medium for the hydrological (water) cycle, creating weather, clouds, and rain.
Protection from Meteors: It acts as a shield, burning up most meteoroids before they can strike the surface.
2. Layers of Atmosphere
The atmosphere is divided into layers based on how temperature changes with altitude.
Temperature decreases as you go up (it's heated from the ground up).
Contains ~80% of the atmosphere's mass and almost all of the water vapor.
This is where all weather (clouds, rain, wind) occurs.
Stratosphere (~12 - 50 km):
Temperature increases as you go up.
This warming is because the Ozone Layer is in this layer, and it absorbs UV radiation from the sun.
This layer is very stable (no weather), which is why airplanes prefer to fly here.
Mesosphere (~50 - 80 km):
Temperature decreases again, reaching the coldest temperatures in the atmosphere (around -90°C).
This is where most meteors ("shooting stars") burn up from friction.
Thermosphere (~80+ km):
Temperature increases dramatically (to >1000°C) due to absorption of high-energy solar radiation.
The air is extremely thin.
This is where auroras (Northern/Southern Lights) occur and where many satellites orbit.
3. Stratospheric Ozone (The "Good" Ozone)
Ozone (O₃) is a molecule made of three oxygen atoms. It's important to know there are two types:
Tropospheric Ozone (Bad Ozone): Found at ground level, it is a major component of smog and is a toxic air pollutant that damages lungs and plants.
Stratospheric Ozone (Good Ozone): Found in the stratosphere (the "ozone layer"), it is essential for life on Earth.
The Ozone Layer is a region in the stratosphere (approx. 15-30 km high) with a relatively high concentration of ozone. Its job is to act as a global sunscreen, absorbing 97-99% of the sun's harmful ultraviolet (UV) radiation, especially UV-B and UV-C, preventing it from reaching the surface.
4. Depletion of Ozone Layer and Ozone Hole
The Problem: Depletion
In the 1970s and 1980s, scientists discovered that the ozone layer was thinning globally, with a severe seasonal depletion over Antarctica, known as the "Ozone Hole."
The Cause: CFCs
The primary culprits were a class of chemicals called Chlorofluorocarbons (CFCs). These were widely used as refrigerants (e.g., in air conditioners, refrigerators), in aerosol spray cans, and as industrial solvents.
The Chemical Process:
CFCs are very stable, so they are not destroyed in the troposphere. They slowly rise to the stratosphere.
In the stratosphere, high-energy UV radiation breaks the CFC molecule apart, releasing a chlorine (Cl) atom.
This chlorine atom acts as a catalyst, starting a destructive chain reaction.
Cl + O₃ → ClO + O₂ (Chlorine destroys an ozone molecule)
ClO + O → Cl + O₂ (The chlorine atom is regenerated, free to destroy another ozone)
A single chlorine atom can destroy up to 100,000 ozone molecules before it is finally removed from the atmosphere.
Consequences of Depletion:
With less ozone, more UV-B radiation reaches the surface, causing:
In Humans: Increased rates of skin cancer, cataracts, and weakened immune systems.
In Ecosystems: Damage to plants (reducing photosynthesis and crop yields) and harm to plankton, the base of the marine food web.
The Solution: The Montreal Protocol (1987)
In a major international success story, the world's nations signed the Montreal Protocol, an agreement to phase out the production and use of CFCs and other ozone-depleting substances. This protocol has been highly effective, and the ozone layer is now slowly beginning to recover.
5. Global Warming and Climate Change
The Greenhouse Effect (Natural vs. Enhanced)
Natural Greenhouse Effect: This is a good, natural process. Greenhouse gases (like H₂O, CO₂, CH₄) in the atmosphere trap some of the outgoing heat from Earth, keeping the planet warm.
Enhanced Greenhouse Effect (Global Warming): Human activities, primarily the burning of fossil fuels (coal, oil, gas), deforestation, and agriculture, have released unprecedented amounts of greenhouse gases, especially CO₂, into the atmosphere. This "thickens the blanket," trapping *too much* heat and causing the planet's average temperature to rise.
Global Warming vs. Climate Change
Global Warming: Refers to the long-term increase in Earth's average surface temperature.
Climate Change: A broader term that refers to all the long-term changes in climate patterns caused by global warming.
Consequences of Climate Change:
Rising Sea Levels: From melting glaciers and polar ice caps, and thermal expansion (warm water takes up more space).
Extreme Weather: More frequent and intense heatwaves, droughts, heavy rainfall (floods), and stronger hurricanes.
Ecosystem Disruption: Species migrating to cooler areas, coral bleaching, and high extinction risks.
Impacts on Agriculture: Shifting growing seasons and crop failures due to drought or floods.
6. Acid Rain
Definition
Acid rain is any form of precipitation (rain, snow, fog, or dry particles) that is unusually acidic, meaning it has a pH lower than normal rain (which is ~5.6). Acid rain can have a pH of 4.2 or even lower.
The Cause
The main cause is the burning of fossil fuels, especially coal (for electricity) and oil (in vehicles).
Burning these fuels releases Sulphur Dioxide (SO₂) and Nitrogen Oxides (NOₓ) into the atmosphere.
These gases react with water, oxygen, and other substances in the atmosphere to form Sulphuric Acid (H₂SO₄) and Nitric Acid (HNO₃).
These strong acids dissolve in water droplets and fall to the Earth as acid rain.
Consequences of Acid Rain:
On Aquatic Ecosystems: Makes lakes and rivers acidic, killing fish, amphibians, and other aquatic life.
On Forests: Damages leaves, leaches essential nutrients (like calcium) from the soil, and releases toxic aluminum, weakening and killing trees.
On Buildings: Corrodes and dissolves limestone, marble (statues, monuments), and metal.