Main Air Pollutants and Atmospheric Layers

Learning Outcomes

  • Distinguish between the different layers in Earth’s atmosphere and list the main atmospheric gases.
  • Recognize the most common air pollutants and their sources.

16.1 Why Is the Atmosphere Multi-Layered?

  • Layers of the Atmosphere: Four distinct layers defined by temperature differences:

    • Troposphere
    • Closest layer to Earth's surface, approximately 10 km high.
    • Contains most of the atmosphere's water vapor; where weather occurs.
    • Uplifting warm air causes turbulence.
    • Stratosphere
    • Extends from Troposphere to about 50 km.
    • Contains ozone that absorbs harmful UV light, warming the stratosphere.
    • Reduced turbulence, allowing for commercial jets and weather balloons.
    • Mesosphere
    • Extends from the stratosphere to 80–90 km.
    • Air is thin; temperatures decrease with altitude, with lows near −90 °C (−130 °F).
    • Comets burn up in this layer.
    • Thermosphere
    • Above the mesosphere, very thin air.
    • High-energy solar radiation interacts with gas atoms, creating auroras.
    • Temperatures can be very high but air is too thin to feel warm.

  • Pressure Changes with Elevation:

    • Atmospheric pressure is densest at the troposphere's base.
    • Increases from about 300 mm Hg at 8,000 m to 760 mm at ground level.
    • Air pressure and oxygen decrease at higher altitudes.

Atmospheric Gases

  • Composition:

    • Oxygen (21%): Vital for life, participates in reactions.
    • Nitrogen (78%): Inert, less involved in reactions.
    • Other gases (1%): Includes argon (0.93%), carbon dioxide (0.04%), and varying water vapor.

  • Particulate Matter:

    • Consists of solid and liquid particles in the air, including natural and man-made sources.

16.2 Common Air Pollutants and Their Sources

  • Sources of Air Pollution:

    • Natural: Wildfires, volcanic eruptions, decaying vegetation.
    • Area: Livestock emissions, urban activities like construction.
    • Stationary: Power plants, oil refineries.
    • Mobile: Vehicles and transport systems.

  • Primary Pollutants:

    • Carbon Oxides (CO, CO₂): From fossil fuel combustion; CO is poisonous and binds with hemoglobin.
    • Nitrogen Oxides (NO₂): Produced during combustion; contributes to ozone formation and acid rain.
    • Sulfur Dioxide (SO₂): From burning sulfur-containing fossil fuels; causes respiratory issues and acid rain.
    • Particulate Matter (PM): Tiny particles from combustion, harming respiratory systems and visibility.
    • Volatile Organic Compounds (VOCs): Emitted from solvents and fuels; some are carcinogenic, others contribute to ozone formation.

  • Secondary Pollutants:

    • Produced when primary pollutants react; include ground-level ozone (O₃), sulfuric acid (H₂SO₄), and nitric acid (HNO₃).

  • Transport of Pollution:

    • Pollution can be transported by winds across vast distances, affecting areas far from the source.

Summary Points

  • Atmosphere has four distinct layers caused by differential heating.
  • Major atmospheric components are nitrogen and oxygen, mainly.
  • Common air pollutants are classified by their source and chemistry, affecting health and environment.