Section 15 vid 1

Atmosphere Structure

• The atmosphere is composed of several layers, each with distinct characteristics and functions.

  • Troposphere

    • Innermost layer: about 0 to 12 kilometers from Earth's surface.

    • Contains 75 to 80% of Earth's air; hosts various pollutants, including photochemical smog from ozone.

    • Thicker at the Equator (about 17 kilometers) and thinner at the poles (about 8 kilometers).

    • Contains turbulent weather patterns and is the narrowest atmospheric layer.

    • Composition: 78% nitrogen, 21% oxygen, 0.9% argon, trace amounts of water vapor, carbon dioxide, neon, helium, hydrogen, methane, and krypton.

  • Stratosphere

    • Extends from 12 kilometers to approximately 50 kilometers.

    • Similar in gas composition to the troposphere but with increased water vapor and ozone concentration.

    • Contains about 90% of atmospheric ozone, often referred to as the ozone layer.

  • Mesosphere

    • Extends from 50 to roughly 80 kilometers.

  • Thermosphere

    • Spans from 80 to 700 kilometers.

  • Exosphere

    • Extends out to 10,000 kilometers.

Temperature Variation Across Layers

• Temperature decreases with altitude in the troposphere.

• In other layers, such as the stratosphere, temperature increases with altitude due to ozone absorption of UV radiation.

• Ozone acts as a thermal cap, maintaining Earth's temperature stability.

Ozone Layer Dynamics

• Ozone Formation

  • Ozone (O₃) forms through the interaction of UV radiation with diatomic oxygen (O₂), photolyzing it into atomic oxygen, which can then combine to form ozone.

• Function of Ozone

  • Prevents about 95% of harmful UVB rays from reaching Earth, allowing for life to thrive.

  • Essential for protecting DNA in living organisms from damage.

  • Regulates thermal stability, contributing to the greenhouse effect.

Ozone Measurements

• Ozone levels measured in Dobson units, developed by meteorologist G. H. Dobson.

  • Thick ozone corresponds to higher molecule concentration per volume.

• Thickness varies with seasons (thicker in March-April, thinner in September-October) and geographical location (thicker above the poles).

Ozone Depletion

• Significant depletion noted beginning in the early 1980s due to chlorofluorocarbons (CFCs) and bromofluorocarbons (BFCs).

  • CFCs are stable compounds that reach the stratosphere and break down under UV light, releasing chlorine and bromine free radicals that damage ozone.

• The Antarctic region is particularly susceptible to ozone depletion due to unique atmospheric conditions and low temperatures, which facilitate the breakdown of ozone.

Health Effects of Ozone

• Tropospheric ozone is harmful and differs from stratospheric ozone. It does not come from the stratosphere but forms at ground level due to UV light reacting with pollutants (nitrogen oxides, hydrocarbons).

• Ozone exposure at the surface can lead to:

  • Damaging effects on human health (respiratory issues including asthma, bronchitis, emphysema).

  • Reductions in crop production and forest growth.

  • Damage to materials (paints, fibers, rubber).

Solutions for Ozone Management

• Reducing fossil fuel combustion is crucial to lowering tropospheric ozone levels.

• Adoption of sustainable practices such as public transport, biking, and walking.

• Seeking energy sources that do not emit ozone-forming pollutants, e.g., solar, hydro, wind energy.

Summary and Importance

• Ozone exists predominantly in the stratosphere and is responsible for UV protection and temperature stabilization in our environment.

• The degradation of the ozone layer poses risks to health, and human actions through the Montreal Protocol have aimed to reverse ozone depletion.