The Chemistry of Earth's Atmosphere and Climate Change

Composition and Evolution of the Earth's Atmosphere

The early Earth's atmosphere was very different from the present day composition. It consisted mainly of hydrogen, methane, ammonia, and water vapor with no free oxygen. Over billions of years, this atmosphere evolved as follows:

• Photosynthesis by early organisms released oxygen and depleted carbon dioxide levels
• Nitrogen levels increased from volcanic activity and decay of ammonia
• Present day atmosphere is 78% nitrogen, 21% oxygen, and trace gases like carbon dioxide, methane, and water vapor

The Greenhouse Effect and Climate Change

The greenhouse effect is a natural process that warms the Earth's surface. Certain gases in the atmosphere like carbon dioxide and methane absorb and trap heat radiated from the planet. This maintains the Earth's temperature suitable for life.

Human activities like burning fossil fuels have increased greenhouse gas levels, amplifying the greenhouse effect. This enhanced greenhouse effect leads to global warming and climate change impacts like rising sea levels, melting glaciers, and extreme weather events.

Atmospheric Pollution From Fuel Combustion

Burning fossil fuels like coal, oil, and natural gas releases several pollutants into the atmosphere:

• Carbon Monoxide (CO): Toxic gas that reduces oxygen carrying capacity of blood
• Sulfur Dioxide (SO2): Causes acid rain and respiratory problems
• Nitrogen Oxides (NOx): Contributes to smog, acid rain, and ozone depletion
• Particulate Matter: Fine particles that damage lungs and heart

These pollutants have detrimental effects on human health, ecosystems, and the environment. Controlling emissions and developing cleaner energy sources is crucial.

Applying Knowledge: Carbon Footprint

Estimate the annual carbon footprint (CO2 emissions in kg) for a four-person household that drives two cars totaling 20,000 km per year and uses 8,000 kWh of electricity from a coal power plant.

Solution:

1. Car emissions: ~150 g CO2/km × 20,000 km = 3,000 kg CO2
2. Electricity emissions: ~1 kg CO2/kWh × 8,000 kWh = 8,000 kg CO2
3. Total carbon footprint ≈ 11,000 kg CO2 per year