Chemistry of the Atmosphere Notes

Chemistry of the Atmosphere

Introduction

  • The atmosphere is a gaseous envelope surrounding Earth.

  • Origin of the word:

    • Greek: atmos (vapor/steam), sphaira (ball/globe)

    • Modern Latin: atmosphaera

Learning Objectives

  • Understand the composition and dynamics of the Earth's atmosphere.

Layers of the Atmosphere

  • Troposphere

    • Closest to Earth's surface (7-18 km above equator).

    • Contains 80% of the atmosphere's mass, including most water vapor (cloud formation).

    • Dominates weather events (rain, lightning, hurricanes).

    • Temperature decreases with altitude.

  • Stratosphere

    • Located 19-50 km above the equator.

    • Contains nitrogen, oxygen, and ozone.

    • Temperature increases with altitude due to exothermic reactions from UV radiation (produces ozone to protect Earth).

  • Mesosphere

    • 30-50 km above the equator.

    • Low concentration of ozone and other gases.

    • Temperature decreases with altitude.

  • Thermosphere (Including Ionosphere)

    • Extends 50-400 km above the equator.

    • Temperature rises with altitude due to energetic particles from the sun.

    • Ionized particles can reflect radio waves.

  • Exosphere

    • Outermost layer, 400 km above the equator, stretching up to 10,000 km.

    • Contains very sparse hydrogen and helium gases.

    • No breathable air; extremely cold temperatures.

Composition of the Atmosphere

  • Total mass of the atmosphere: ~5.3 x 10^18 kg

  • Water concentration varies significantly based on location.

Nitrogen Cycle

  • Nitrogen must be fixed to be usable by plants and animals.

    • Nitrogen Fixation: Conversion of atmospheric nitrogen into usable forms (e.g., nitrates).

    • Atmospheric nitrogen fixation:

      • NO + O2 → NO2 → HNO2 + HNO3 (through lightning and other processes).

    • Nitric acid is transformed into soil nitrates, utilized by flora and fauna for biological necessities.

    • Denitrification: Returns nitrogen back to the atmosphere via the decomposition of organic matter.

  • Process Breakdown:

    • Industrial nitrogen fixation:

    • N2 + 3H2 → 2NH3 (ammonia used in fertilizers).

Oxygen Cycle

  • Complicated due to various chemical forms of oxygen.

  • Oxygen is consumed through:

    • Respiration and industrial combustion (producing CO2).

  • Photosynthesis: Major mechanism regenerating atmospheric oxygen from CO2 and water.

Auroras

  • Result from solar flares ejecting electrons and protons, which collide with Earth's upper atmosphere, leading to ionization.

  • Types of Aurora:

    • Aurora Borealis: Northern Hemisphere.

    • Aurora Australis: Southern Hemisphere.

  • During the excitation and return of molecules to lower energy states, light is emitted:

    • Excited oxygen emits green and red photons; nitrogen emits blue and violet light.

These notes encapsulate fundamental concepts regarding the chemistry of the atmosphere, including its composition, the cycling of gases, and phenomena like auroras. Use these bullet points to study and prepare for your exam effectively.