Lecture Notes: Photochemical Smog and Thermal Inversions

Introduction

• Course: AP Environmental Science
• Topics Covered:
  • Photochemical Smog (Topic 7.2)
  • Thermal Inversions (Topic 7.3)
• Enduring Understanding: Human activities have physical, chemical, and biological consequences for the atmosphere.

Learning Objectives

• Photochemical Smog: Explain its causes, effects, and reduction methods.
• Thermal Inversions: Describe and relate them to pollution.

Smog

• Definition: Smog is a combination of smoke and fog.
• Types:
  • Winter Smog: Occurs during winter due to increased energy demands and burning of fossil fuels, creating smoke and particulate matter.
  • Summer Smog (Photochemical Smog): Occurs when sunlight reacts with water and pollutants.

Winter Smog

• Causes:
  • Burning of wood, coal, and fossil fuels.
  • Increased energy demands during winter.
• Exacerbation:
  • Thermal Inversions: Trap cold air and pollutants in valleys.

Thermal Inversions

• Normal Condition: Temperature decreases with altitude.
• Inversion Condition: Cold air trapped under warm air, often in valleys, preventing pollutant dispersion.
• Example: Denver experiencing distinct layers of smog.

Summer Smog (Photochemical Smog)

• Formation: Sunlight reacts with water vapor and primary pollutants (e.g., nitrous oxides, VOCs) to create secondary pollutants (e.g., ozone, nitric acid).
• Major Components:
  • Ozone (O3)
  • Nitric Acid (HNO3)
• Contributing Factors:
  • Sunlight, heat, humidity, and primary pollutants.

Characteristics

• Occurrence: More common in sunny, warm, and dry areas; peaks during summer.
• Variability: Varies throughout the day; ozone peaks at midday.
• Examples:
  • Global: Tropical and populous cities.
  • USA: Predominantly in California and Texas.

Human Health Effects

• Affected Groups: Young, old, those with pre-existing conditions.
• Symptoms: Irritation of mucus membranes; respiratory issues like asthma and bronchitis.
• Serious Impacts: Potential long-term effects include cancer, Alzheimer's, birth defects, and premature death.

Solutions

• Renewable Energy: Reduces reliance on fossil fuels.
• Emission Reductions: Efficiency standards, catalytic converters, and pollution-capturing devices.
• Behavioral Changes: Conserve energy, monitor air quality, and use eco-friendly products.
• Innovative Technologies: Smog filtering towers and catalytic buildings.

Essential Knowledge Recap

• Photochemical Smog: Formed from reactions involving nitrogen oxides and VOCs with sunlight.
• Environmental Impact: Influenced by sunlight, heat, and precipitation.
• Reduction Methods: Focus on reducing precursor emissions (NOx, VOC).
• Thermal Inversions: Exacerbate pollution by trapping pollutants.

End of Lecture

This concludes the lecture notes on photochemical smog and thermal inversions. Remember to review the key concepts and learning objectives discussed.