3.1 The Atmosphere

The Atmosphere

What is it?

  • The atmosphere is the layer of gases surrounding Earth, retained by Earth's gravity.

  • It plays a crucial role in protecting life by:

    • Absorbing ultraviolet solar radiation

    • Warming the surface through the greenhouse effect

    • Reducing temperature extremes between day and night (diurnal temperature variation)

Atmosphere Composition

  • Dry air composition (by volume):

    • 78.09% nitrogen

    • 20.95% oxygen

    • 0.93% argon

    • 0.039% carbon dioxide

    • Small amounts of other gases

  • Air also contains variable water vapor.

  • Life-sustaining air is primarily found in Earth's troposphere and artificial environments.

Layers of the Atmosphere

  • Exosphere (550-600 km): Upper limit of the atmosphere; satellites orbit here.

  • Thermosphere (95 km): Extremely hot (about 1000°C); major site for auroras and where the space shuttle orbits.

  • Mesosphere (48 km): Temperature decreases to about -90°C; meteors burn up in this layer.

  • Stratosphere (11 km): Stable air; home to the ozone layer that absorbs harmful UV radiation; highest temperature reaches about 0°C.

  • Troposphere: Lowest layer; contains most clouds and weather phenomena.

Air Pollution

  • Main Issues: Various pollutants cause significant health and environmental issues.

Criteria Pollutant Gases Affecting Health

  • Carbon monoxide (CO):

    • Sources: Incomplete combustion of fossil fuels.

    • Health effects: Prevents oxygen transport in the blood, leading to circulatory issues.

  • Sulfur Dioxide (SO2):

    • Sources: Burning fossil fuels, volcanic eruptions.

    • Health effects: Causes respiratory problems.

  • Nitrogen Dioxide (NO2):

    • Sources: Transportation, electricity generation, industrial activity.

    • Health effects: Respiratory problems.

  • Particulate Matter (PM):

    • Sources: Burning fuels, pollen, and fertilizers.

    • Health effects: Respiratory issues.

  • Lead (Pb):

    • Sources: Previously in pipes, paints, gasoline, now from burning fossil fuels.

    • Health effects: Damages the central nervous system.

  • Ozone (O3):

    • Health effects: Causes respiratory and immunology problems.

Greenhouse Effect

  • Earth receives energy from the sun as sunlight. The surface absorbs this energy, heating up. The Earth cools down by emitting infrared radiation.

  • Greenhouse gases absorb some of this radiation, keeping the atmosphere warm and consequently warming the Earth's surface.

Greenhouse Effect Energy Flow

  • Solar radiation absorbed by Earth leads to emission of longwave (infrared) radiation.

  • Various rates of energy absorption:

    • Incoming solar radiation: 343 Watts/m²

    • Reflected solar radiation: 103 Watts/m²

    • Outgoing infrared radiation: 240 Watts/m²

    • Absorption by greenhouse gas molecules affects temperature.

Major Greenhouse Gases and Human Activities

  • Carbon Dioxide: 54.7% of U.S. greenhouse gas emissions.

  • Methane: 28% of emissions.

  • Nitrous oxide: 4.9%.

  • Fluorinated gases and other contributions: significant but lesser percentages from various sectors such as transportation, electricity generation, agriculture.

Ozone Layer

  • Located in the stratosphere, it absorbs harmful UV radiation from the sun.

  • Depletion of the ozone layer is a concern due to increased UV radiation reaching Earth, risking skin cancer and affecting various life forms.

  • Chlorofluorocarbons (CFCs) are major contributors to ozone layer damage.

Ozone Layer Depletion Process

  1. UV rays split CFC molecules, releasing chlorine atoms.

  2. Chlorine breaks down ozone (O3) molecules, creating oxygen (O2) and leaving chlorine monoxide (ClO).

  3. Various ozone-depleting chemicals include:

    • CFCs (aerosols, refrigerants)

    • HCFCs (used in similar contexts)

    • Halons (fire extinguishers)

    • Methyl bromide (pesticides)

References

  • Links to additional resources and readings on atmospheric science, air pollution, and greenhouse effects.