9. Chemistry of the Atmosphere

5.9 Chemistry of the Atmosphere
The Earth's atmosphere is dynamic, changing due to natural cycles and human activity. Scientists use complex software to predict weather and climate change. Solutions are needed to reduce human impact from air pollutants.

5.9.1 The composition and evolution of the Earth's atmosphere

5.9.1.1 Proportions of gases today
~80% nitrogen, ~20% oxygen, small amounts of carbon dioxide, water vapor, and noble gases.

5.9.1.2 The Earth's early atmosphere
Early atmosphere formed by volcanic gases: mainly carbon dioxide, some nitrogen, methane, ammonia, and water vapor. Oceans formed as water vapor condensed, dissolving CO2 and reducing its atmospheric amount.

5.9.1.3 How oxygen increased
Oxygen produced by algae and plants via photosynthesis starting ~2.7 billion years ago, increasing atmospheric oxygen and allowing animals to evolve.

5.9.1.4 How carbon dioxide decreased
Photosynthesis by plants/algae reduced CO2. Formation of sedimentary rocks, fossil fuels like coal and oil also reduced atmospheric CO2.

5.9.2 Carbon dioxide and methane as greenhouse gases

5.9.2.1 Greenhouse gases
Water vapor, carbon dioxide, and methane trap heat in the atmosphere, maintaining Earth's temperature to support life.

5.9.2.2 Human activities increasing greenhouse gases
Carbon dioxide increased by burning fossil fuels and deforestation. Methane increased by agriculture (e.g., livestock) and landfill sites.

5.9.2.3 Global climate change
Rising average global temperatures cause climate change with effects like sea level rise, extreme weather, and loss of habitats.

5.9.2.4 Carbon footprint and reduction
Carbon footprint = total greenhouse gases emitted over a product or event’s life. Reduced by cutting CO2 and methane emissions through lifestyle and technology changes, though some actions have limitations.

5.9.3 Common atmospheric pollutants and their sources

5.9.3.1 Pollutants from fuels
Burning fuels releases carbon dioxide, water vapor, carbon monoxide, sulfur dioxide, nitrogen oxides, soot, and unburned hydrocarbons.

5.9.3.2 Properties and effects of pollutants

  • Carbon monoxide: toxic, colorless, odorless gas.

  • Sulfur dioxide and nitrogen oxides: cause respiratory problems and acid rain.

  • Particulates: cause global dimming and health issues.