7.2 APES notes

Photochemical Smog

Skill Demonstrated 5.B

  • Description: Describe relationships among variables represented in data.

Enduring Understanding STB-2

  • Concept: Human activities have physical, chemical, and biological consequences for the atmosphere.

Learning Objective STB-2.B

  • Goal: Explain the causes and effects of photochemical smog and methods to reduce it.

What is Smog?

  • Definition: Smog is a type of air pollution that combines smoke and fog, often aggravated by weather conditions.

Types of Smog

  1. Photochemical Smog (LA Smog / Brown Smog)

    • Composed of secondary pollutants formed from the reaction of sunlight with nitrogen oxides (NOx) and volatile organic compounds (VOCs).
    • Characterized by a brown haze primarily due to the presence of ozone (O3).

  2. Sulfurous Smog (London Smog / Gray Smog)

    • Composed chiefly of sulfur dioxide (SO2) and particulate matter, often linked to high coal combustion in cold weather.
    • Typically appears gray, resulting from the mixing of fog and particulate pollution.

Normal Ozone Formation

  • Ozone Generation: Ozone is produced early in the day.
  • Peak Concentration: Ozone levels peak in the afternoon and during summer months due to increased sunlight exposure.

Precursors of Photochemical Smog

  • Main Ingredients: The formation of photochemical smog relies on:

    1. Nitrogen Oxides (NOx)
    • Sources: Produced from industrial processes, automobiles, and trucks.
    • Reaction: Under sunlight, NO2 breaks down into nitrogen monoxide (NO) and free oxygen (O).
    • Result: Free oxygen binds with O2 to form O3 (ozone).
    1. Volatile Organic Compounds (VOCs)
    • Sources: Emitted from refineries, manufacturing, gas stations, and vehicles.
    • Role: VOCs react with NO, contributing to the generation of photochemical oxidants.

  • Secondary Pollutant: Ozone acts as a secondary pollutant, formed when NO2 breaks down under sunlight and free O binds with O2.

  • Process: Pollutants "bake" together in direct sunlight to create smog.

Conditions for Smog Formation

  • Factors Influencing Formation:
    • Sunlight: Essential for the transformation of NO2 into NO + O, critical for ozone formation.
    • Warmth: Higher temperatures increase the rate of ozone formation and evaporation of VOCs, further intensifying smog production.

Characteristics of Photochemical Smog

  • Definition: Photochemical smog is generated when ultraviolet (UV) light from the sun reacts with nitrogen oxides and VOCs.
  • Visible Effects: Results in a brown haze, particularly evident in the morning and afternoon, predominantly in warm, densely populated urban areas.
  • Composition: Includes both primary pollutants (NOx and VOCs) which enter the atmosphere and secondary pollutants such as ozone (O3) that arise from chemical reactions.

Role of Vehicles in Smog Formation

  • Contributing Factors: Motor vehicles are a significant source of emissions that introduce primary pollutants into the atmosphere.
  • Urban Concentration: Photochemical smog is more common in urban settings due to the high volume of vehicle traffic.

Understanding Volatile Organic Compounds (VOCs)

  • Definition: Organic compounds with high vapor pressure at room temperature, leading to a significant number of molecules evaporating from their liquid or solid forms.
  • Characteristics:
    • Can be man-made or occur naturally.
    • Associated with many scents and odors.
    • Important for plant communication and can pose health risks to humans and the environment.

Common Sources of VOCs

  • Household and Daily Activities:
    • Products such as hairspray, deodorant, perfume, and cleaners.
    • Activities including cooking, driving, dry cleaning, smoking, and burning wood.
    • Common consumer items include cosmetics, paints, varnish, and building materials.

Formation of Photochemical Smog

  • Location: Occurs at ground level in the troposphere.
  • Impact on Air Quality: Leads to poor air quality, which can result in respiratory problems and eye irritation.

Daily Variation of Tropospheric Ozone

  • Production Timing:
    • Nitrogen oxide is produced early in the day.
    • Ozone concentration peaks in the afternoon, especially in summer due to increased rates of chemical reaction with sunlight.

Factors Increasing Smog Formation

  1. Increased Traffic: Vehicles are a primary source of NO2 emissions.
  2. Higher VOC Emissions: Industrial emissions from factories and additional gas stations.
  3. Warmer Temperatures: Particularly in summer and during afternoon hours.
  4. Urban Areas: Higher traffic congestion, low albedo effect, and urban heat island phenomenon contribute to smog development.

Environmental Impacts of Smog

  • Effect on Photosynthesis: Reduces sunlight availability, negatively impacting photosynthesis in plants.
  • Harm to Flora: O3 can damage plant tissues by affecting stomatal function, leading to “cellular damage.”
  • Impact on Fauna: Acts as a respiratory irritant to animals.

Human Health Impact of Smog

  • Health Issues: Respiratory irritants worsen chronic conditions like asthma, bronchitis, and chronic obstructive pulmonary disease (COPD); can also irritate the eyes.
  • Economic Consequences: Higher healthcare costs to treat ailments and decreased agricultural yield as less sunlight permeates crops due to smog.

At-Risk Populations

  • Individuals with Increased Health Risks:
    • Pregnant women
    • Seniors
    • Individuals with heart/lung conditions or diabetes
    • Children and infants at risk of asthma and other respiratory illnesses.
  • Health Effects:
    • Breathing ozone can cause chest pain, coughing, throat irritation, and worsen respiratory conditions.
    • Inhalation of particulate pollution can result in respiratory and cardiovascular diseases, potentially leading to death.

Methods to Reduce Smog

  1. Vehicle Modifications:
    • Decrease the number of vehicles on the road, promoting public transport and increasing the use of electric vehicles.
  2. Energy Changes:
    • Elevate production from renewable energy sources (e.g., wind, solar) to limit NOx emissions.
    • Switch from coal to cleaner alternatives like natural gas or nuclear power plants that emit less NO2.
  • Goal: Reducing nitrogen oxide and VOC emissions is critical for mitigating photochemical smog effects.

Summary and Action Items

  • To Do:
    • Watch all AP Classroom videos for Topic 7.2 to reinforce learning.
    • Ensure understanding of:
    • The causes of photochemical smog.
    • Environmental and human health-related effects.
    • Identify methods to mitigate smog.