Greenhouse Gases & Ozone Layer
Chapter 2: Environmental Issues - Greenhouse Gases (GHGs) Part 3
🌍 Greenhouse Gases (GHGs)
Definition and Mechanism:
Greenhouse gases (GHGs) are special gases in the air that make the Earth's surface warmer. They work like a blanket. Just like a blanket keeps you warm by trapping your body heat, greenhouse gases trap the heat that the Earth gives off after being warmed by the Sun.
How Greenhouse Effect Works
1. Sunlight Warms Earth
The Sun shines on the Earth and warms it up.
2. Earth Gives Off Heat
The Earth's surface gives off thermal radiation.
3. Gases Trap Heat
GHGs absorb infrared radiation and trap heat.
Temperature Impact:
Without greenhouse gases, Earth would be -18°C (0°F), but thanks to them, it's a much warmer 15°C (59°F).
📝 Important Exam Points
- • Greenhouse gases primarily absorb infrared radiation from the solar spectrum.
- • Greenhouse gases, including water vapor, absorb the earth's thermal radiation and contribute to global warming.
- • Earth's climate was changing even before man appeared on earth.
- • CO₂, H₂O, CH₄, and O₃ are Natural GreenHouse Gases (GHGs).
💨 Main Greenhouse Gases
💧 1. Water Vapor (H₂O)
- ▸ Naturally occurring, part of the water cycle.
- ▸ Most abundant greenhouse gas; increases with temperature, amplifying warming.
- ▸ Traps heat, contributing to climate change but is short-lived and regulated by natural processes.
⚫ 2. Carbon Dioxide (CO₂)
- ▸ Released from burning fossil fuels & deforestation.
- ▸ Has a long atmospheric lifetime and accumulates over time.
⚠️ Exam Important:
- • Major contribution to greenhouse effect comes from CO₂.
- • CO₂ has the maximum contribution to Global Warming.
🔥 3. Methane (CH₄)
- ▸ Emitted from agriculture, fossil fuel production, and waste.
- ▸ More effective at trapping heat than CO₂ (higher GWP) but has a shorter lifespan.
⚠️ Exam Important:
- • Methane is emitted from wetlands.
- • CH₄ helps in formation of Ozone and is a Volatile Organic Compound (VOC).
🧪 4. Nitrous Oxide (N₂O)
- ▸ Produced from fertilizers & industrial activities.
⚠️ Exam Important:
- • N₂O has significantly higher Global Warming Potential (GWP) compared to CH₄, CO₂, and CO.
- • Note: Distinguish between Nitrous Oxide (N₂O - GHG) and Nitrogen Dioxide (NO₂ - Pollutant).
- • Nitrogen dioxide causes aggravation of respiratory disease and atmospheric discolouration.
🛡️ 5. Ozone (O₃)
- Forms from reactions with pollutants & sunlight.
- ▸ Harmful at ground level (smog), but protects against UV in the stratosphere.
☢️ 6. Chlorofluorocarbons (CFCs)
- ▸ CFCs are potent greenhouse gases.
- ▸ Stable greenhouse gases that vaporize just below room temperature.
- ▸ Can destroy ozone and catalytically destroy ozone in the stratosphere.
- ▸ Chlorofluorocarbon is a non-vehicular pollutant.
⚠️ Exam Important:
- • Discovery of Ozone hole was first made over Antarctic.
- • CFC concentration has been decreasing due to Montreal Protocol.
- • However, CFCs already present will persist for many years.
⚡ 7. Sulfur Hexafluoride (SF₆)
- ▸ Used in electrical insulation & semiconductor industry.
- ▸ Strongest greenhouse gas per molecule with an extremely long atmospheric lifetime.
📊 Global Warming Potential (GWP)
Definition:
Global Warming Potential (GWP) is a way to compare how much heat different greenhouse gases trap in the atmosphere over a specific period (usually 100 years).
⚠️ Exam Important:
Carbon dioxide (CO₂) is used as the reference gas for Global Warming Potential (GWP) and is assigned a GWP value of 1.
🔄 Variability
⚠️ Exam Important:
- • Global warming potential of a molecule of a greenhouse gas over different time spans of decades to 100 years may vary significantly.
- • Some greenhouse gases have shorter lifetimes compared to carbon dioxide.
🏆 GWP Rankings (Lowest to Highest)
⚠️ Exam Important:
The gases increase in GWP in this order: CO₂ < CH₄ < N₂O < CFCs
1. Carbon dioxide (CO₂)
Baseline, GWP = 1
2. Methane (CH₄)
GWP = 28–36
3. Nitrous oxide (N₂O)
GWP = 265–298
4. Chlorofluorocarbons (CFCs) / HFCs
GWP = Thousands (e.g., CFC-11 is ~4,660)
5. Sulfur hexafluoride (SF₆)
GWP = 23,500 (Strongest per molecule)
⏰ Atmospheric Lifetime
The longevity of gases in the atmosphere varies.
⚠️ Exam Important:
The correct order for decreasing atmospheric lifetimes:
CFC-11 > Nitrous oxide (N₂O) > Methane (CH₄) > Surface ozone (O₃)
CFC-11
~50-100 years
Longest
N₂O
~114 years
CH₄
~12 years
O₃
Days to weeks
Shortest
🌏 Global Emissions and Human Activity
Since people started using machines and factories around 1750, emissions have skyrocketed.
⚠️ Exam Important:
China is the largest emitter of Greenhouse Gases (GHGs) at present.
Top 10 Countries by GHG Emissions (Largest to Lowest)
🇨🇳 China
Largest emitter, coal-dependent
🇺🇸 USA
High energy consumption
🇮🇳 India
Rapidly growing, coal reliance
🇷🇺 Russia
Oil and gas
🇯🇵 Japan
Energy-intensive industries
🇩🇪 Germany
Industrial emissions
🇮🇷 Iran
Oil and gas production
🇰🇷 South Korea
Industrial sector
🇸🇦 Saudi Arabia
Oil extraction
🇮🇩 Indonesia
Deforestation and peatland
⚠️ Impacts of Greenhouse Gases
🌡️ Global Warming
- ▸ Carbon Dioxide causes about three-quarters of global warming.
- ▸ Scientists warn that exceeding a 2.0°C rise could be dangerous.
🌊 Sea Level Rise
⚠️ Exam Important:
- • Thermal expansion of oceans may lead to Sea level rise.
- • Over the past 100 years, the estimated rise of global sea level is by 10-25cm or more.
- • Thermal expansion of ocean waters has the maximum contribution in it.
Greenhouse Gas Comparison
* GWP values are relative to CO₂ over 100-year timeframe
📚 Quick Summary
Natural GHGs:
CO₂, H₂O, CH₄, O₃
Highest GWP:
CFCs > N₂O > CH₄ > CO₂
Maximum Global Warming:
Carbon Dioxide (CO₂)
Most Abundant:
Water Vapor (H₂O)
🛡️ Ozone Layer: General Overview
🌐 Structure & Function
📍 Location:
⚠️ Exam Important:
- • The ozone layer is located in the Stratosphere, 15-35 km above Earth.
- • Ozone layer which protects us from harmful ultraviolet radiations is situated in Stratosphere.
⚠️ Ozone Depletion
🔬 Mechanism
💡 Simple Explanation: Imagine the ozone layer as a sunscreen. Chemicals like Chlorofluorocarbons (CFCs) break it apart.
⚠️ Exam Important:
• Ultraviolet radiation photolysis the ozone into other components.
Ozone Depletion Process
CFCs Released
CFCs reach the stratosphere
UV Breaks CFCs
Sunlight breaks CFCs releasing Chlorine
Chlorine Destroys O₃
One Cl destroys 100,000 O₃ molecules
🕳️ Ozone Hole
⚠️ Exam Important:
- • Ozone hole appears over Antarctica mostly in the month of September.
- • Polar Stratospheric Clouds are associated with Ozone layer depletion environmental issues.
🏙️ Urban Heat Island Effect
⚠️ Exam Important:
- • Nighttime temperatures in the central parts of a city are generally higher than those over the surrounding rural areas.
- • Radiation losses over the urban areas are less than that over the rural Areas.
🧊 Methane & Permafrost
⚠️ Exam Important:
- • Global warming could lead to increased release of the greenhouse gas, Methane.
- • There is a large amount of Methane currently frozen in the permafrost in the far northern regions of the world.