Air Pollution Overview

Chapter 5: Air Pollution

Major Pollutants in Our Air

  • Criteria Pollutants: The U.S. Clean Air Act identifies six major air pollutants:
    • Sulfur Dioxide (SO2): Formed from burning fossil fuels (coal, oil).
    • Nitrogen Oxides (NOx): Formed at high temperatures in combustion processes, contributes to smog and acid rain.
    • Carbon Monoxide (CO): Produced by incomplete combustion, a toxic gas that interferes with oxygen transport in blood.
    • Ozone (O3): Beneficial in the stratosphere (blocks UV), harmful at ground level (contributes to smog).
    • Particulate Matter (PM10, PM2.5): Includes solid particles and liquid droplets. Health risks increase with smaller particles.
    • Lead (Pb): Neurotoxic metal, major source from burning of fossil fuels, particularly coal.

Sources of Air Pollution

  • Natural Sources: Volcanoes, vegetation release VOCs, and sea spray.
  • Anthropogenic Sources: Primary pollutants (directly emitted) vs. secondary pollutants (formed by reactions in the atmosphere).
  • Criteria Pollutant Sources:
    • SO2: 2 million tons from stationary combustion
    • NOx: 9 million tons from stationary combustion and vehicles
    • CO: 64 million tons primarily from transportation
    • VOCs: 17 million tons from various sources (both natural and anthropogenic)
    • Particulate Materials: 17 million tons from various activities.

Atmospheric Processes

  • Troposphere: The lowest layer of the atmosphere where weather occurs. Air temperature decreases with altitude.
  • Tropopause: The boundary between the troposphere and the stratosphere, restricting vertical mixing.

Industrial & Photochemical Smog

  • Industrial Smog: Results from the burning of coal, primarily composed of SO2 and PM.
  • Photochemical Smog: Initiated by sunlight, involves VOCs and NOx leading to ozone formation. Secondary pollutants infused, contributing to urban air quality issues.

Acid Rain

  • Definition: Rain (or precipitation) that has a pH lower than 5.6. Formed from sulfuric acid (H2SO4) and nitric acid (HNO3), primarily due to pollution.
  • Effects: Can damage forests, wildlife, and structures/materials (e.g., limestone, marble).

Control of Air Pollution

  • Legislation: The Clean Air Act regulates pollutants.
  • Pollution Control Methods:
    1. Electrostatic Precipitation: Uses electrical charges to remove particles from exhaust.
    2. Bag Filtration: Captures particulates using fabric bags similar to vacuum cleaners.
  • Trends in U.S. Air Quality: Air quality has improved in recent decades, with reductions in emission levels of criteria pollutants.

Effects of Air Pollution

  • Health Impacts: WHO estimates linked millions of premature deaths to air pollution, particularly from PM2.5 exposure.
    • Risks include respiratory diseases, heart attacks, and complications in fetal development.

Indoor Air Pollution

  • Often higher concentrations of toxic pollutants compared to outdoors due to materials in use at home (e.g., formaldehyde, benzene).
  • Common Indoor Pollutants: Asbestos, CO, lead, nitrogen dioxide, VOCs, etc.