Air
Section: 10. Chemistry of the Environment | Syllabus: Cambridge AS Level Physics 9702
Air Air Composition Air is a mixture of gases with relatively constant proportions. The main components are nitrogen and oxygen, with smaller amounts of noble gases and carbon dioxide. Composition of Clean, Dry Air Nitrogen (N₂): Approximately 78% Oxygen (O₂): Approximately 21% Noble gases (mainly Argon): Approximately 1% Carbon dioxide (CO₂): Approximately 0.04% (variable, increasing due to human activity) Gas Percentage Source/Role Nitrogen (N₂) ~78% Relatively unreactive; essential for proteins in living organisms Oxygen (O₂) ~21% Essential for respiration and combustion Noble gases (Ar, Ne, etc.) ~1% Chemically unreactive; used in lighting and welding Carbon dioxide (CO₂) ~0.04% Product of respiration and combustion; used in photosynthesis Air Pollutants Various human activities release pollutants into the atmosphere: Pollutant Main Sources Adverse Effects Carbon dioxide (CO₂) Combustion of fossil fuels, deforestation Greenhouse gas; causes global warming and climate change Carbon monoxide (CO) Incomplete combustion of fossil fuels Toxic gas; binds to hemoglobin, preventing oxygen transport Particulates (soot, smoke) Combustion of fossil fuels, diesel engines Respiratory problems, reduced visibility, global dimming Methane (CH₄) Agriculture (livestock), landfills, rice paddies Greenhouse gas; more potent than CO₂ Nitrogen oxides (NOₓ) Car engines, industrial processes Respiratory problems, acid rain, photochemical smog Sulfur dioxide (SO₂) Combustion of fossil fuels containing sulfur Respiratory problems, acid rain, damages buildings Key Environmental Issues Global warming: Greenhouse gases trap heat in the atmosphere, raising global temperatures Respiratory problems: Particulates and gases like SO₂ and NOₓ irritate airways and lungs Acid rain: SO₂ and NOₓ dissolve in rainwater, forming acidic solutions that damage ecosystems and structures
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