Lecture Notes: Photochemical Smog - IB ESS Topic 6.3

Introduction to Photochemical Smog

• Part of main IB ESS Topic 6: Atmospheric Systems and Society
• Significant Idea 1: Combustion of fossil fuels produces primary pollutants, leading to secondary pollutants and photochemical smog.
• Types of Smog:
  • Industrial Smog: Formed by combustion of fossil fuels.
  • Photochemical Smog: Formed when ozone, nitrogen oxides, and gaseous hydrocarbons interact with sunlight.

Primary Pollutants

• Produced from combustion of fossil fuels.
• Examples:
  • Carbon monoxide (CO)
  • Carbon dioxide (CO2)
  • Black carbon (soot)
  • Unburned hydrocarbons
  • Oxides of nitrogen (NOx)
  • Oxides of sulfur
• Soot:
  • Black carbon particles from incomplete combustion.
  • Contains polycyclic aromatic hydrocarbons (PAHs) and heavy metals.
  • Not water-soluble, can enter bloodstream, causing health issues.
  • Contributes to global warming and melting glaciers.

Volatile Organic Compounds (VOCs)

• Easily become vapors/gases from burning fuels and consumer products.
• Health Impacts:
  • Asthma, itchy eyes, sneezing, headaches.
  • Long-term exposure can cause kidney damage and elevated blood pressure.
• React with nitrogen oxides to form secondary pollutants like particulates and tropospheric ozone.

Secondary Pollutants

• Formed when primary pollutants react with chemicals in the atmosphere.
• Examples:
  • Tropospheric ozone (major component of smog)
  • Aldehydes
  • Sulfuric acid and nitric acid (acid rain components)
• Tropospheric Ozone:
  • Formed from oxygen molecules and atoms, nitrogen dioxide, and VOCs in sunlight.
  • Damages crops, health, fabrics, and contributes to global warming.
  • Causes premature deaths and chronic diseases.

Factors Influencing Smog Levels

• Local topography, climate, population density, and fossil fuel use.
• Snapshots of air quality index values indicate variations in smog severity globally.
• Thermal Inversions:
  • Warm air traps cooler air near ground, preventing pollutants from rising.
  • Common in winter, exacerbates air quality issues.

Societal and Environmental Impacts

• Health decline, economic losses significant due to urban air pollution.
• Air pollution is a leading risk factor for deaths worldwide (higher than malaria and AIDS).
• Lost labor income due to premature deaths affects economic development.

Pollution Management Strategies

1. Altering Human Activity:
   • Use energy-efficient technologies, public transit, and cycling.
   • Reduce VOC products, use electric vehicles.
2. Regulating Pollutants:
   • Government regulations like the U.S. Clean Air Act.
   • Use of catalytic converters and cleaner fuels.
3. Cleanup Measures:
   • Reforestation, regrading, and conservation efforts.
   • Innovations like the Smog Free Tower.

Case Study: The U.S. Clean Air Act

• Major success in vehicle pollution control.
• New vehicles have drastically reduced emissions compared to the 1960s.
• Air quality in U.S. cities improved despite increasing population and miles traveled.
• Economic benefits: $1 spent on emission reduction yields $9 in benefits.

Conclusion

• Photochemical smog is a complex environmental issue with significant health, societal, and economic impacts.
• Effective management requires a combination of altering human behavior, regulatory measures, and innovative solutions.
• Further study and resources available in the IB ESS textbook and related materials.