Atmospheric Gases — Key Constituents and Roles

Major Gases by Abundance

• Nitrogen (N_2): 78\%; largely inert.
• Oxygen (O_2): 20\%-21\%; essential for respiration.
• Water vapor (H_2O(g)): variable; drives weather.
• Argon (Ar): \approx 1\%; nonreactive.
• Carbon dioxide (CO_2): 0.3\%; greenhouse gas.
• Trace gases (Neon, Helium, Methane, Hydrogen, Nitrous oxide, Ozone): small amounts; contribute to atmospheric properties and UV protection (ozone).

Greenhouse Gases

• Water vapor, carbon dioxide, and methane trap heat.

Takeaway

• The atmosphere is mostly nitrogen (78\%) and oxygen (20\%-21\%); other gases, though minor, are crucial for weather, climate, and UV protection.