7.1 Study Notes on Air Pollution

Topic 7.1: Introduction to Air Pollution

Overview

  • Skill Demonstrated: 4.E Explain modifications to an experimental procedure that will alter results.
  • Enduring Understanding: STB-2 Human activities have physical, chemical, and biological consequences for the atmosphere.
  • Learning Objective: STB-2.A Identify the sources and effects of air pollutants.

Types of Air Pollution

  • Outdoor Pollution: Includes types, sources, control, and monitoring.
  • Indoor Pollution: Includes sources and control mechanisms.

Categories of Air Pollutants

  • Primary Pollutants: Emitted directly into the atmosphere.
  • Secondary Pollutants: Formed through reactions in the atmosphere.

6 Criteria Air Pollutants (Clean Air Act 1970)

The Clean Air Act identified six criteria air pollutants which the EPA monitors and regulates:

  • SO2: Sulfur Dioxide
  • NOx: Nitrogen Oxides
  • CO: Carbon Monoxide
  • PM: Particulate Matter
  • O3: Ozone
  • Pb: Lead

The Clean Air Act: Lead Regulation

  • History of Lead in Gasoline:

    • Lead was added to gasoline since the early 1920s.
    • EPA issued reduction standards in 1973 for gradual phase-down to 0.1 g/gal by 1986.
    • 1973: Average lead content was 2-3 g/gal, ~200,000 tons/year.

  • Impactful Regulations:

    • 1975: Introduction of emission control systems, including catalytic converters requiring lead-free fuel.
    • By 1995: Leaded fuel made up only 0.6% of gasoline sales, < 2,000 tons/year.
    • 1996 Ban: Sale of leaded fuel for on-road vehicles banned; allowed for off-road uses (aircraft, racing, etc.).

Recent Updates on the Clean Air Act (February/March 2026)

  • Deregulation Highlights:
    • Endangerment Finding Rescinded: In 2026, EPA repealed the finding that GHGs threaten public health, affecting motor vehicle standards.
    • Vehicle Emission Standards: Repealed all standards since 2010 for light and heavy-duty vehicles.
    • Power Plant Rules: Reversed strengthened Mercury and Air Toxics Standards (MATS) for coal-fired plants.
    • NOx Regulations Weakened: New rules reduce protections for nitrogen oxide emissions.
    • Legal Shift: Reinterpretation of the Clean Air Act regarding GHG emissions not authorized for regulating climate change.

Importance of the Clean Air Act

  • The Clean Air Act significantly regulated lead usage, resulting in a dramatic decrease of atmospheric lead exposure.

Detailed Analysis of the 6 Criteria Air Pollutants

NOx (Nitrogen Oxides)
  • Main Source: Combustion of fossil fuels, particularly from vehicles.
  • Human Impact: Acts as a respiratory irritant, aggravating asthma, causing airway inflammation, and worsening cough.
  • Environmental Impact:
    • Primary pollutant of photochemical smog and acid precipitation.
    • NO2 contributes to Tropospheric Ozone (O3).
SO2 (Sulfur Dioxide)
  • Main Source: Coal combustion (electricity generation), volcanic eruptions, and metal smelting.
  • Human Impact: Respiratory irritant worsening asthma and bronchitis.
  • Environmental Impact:
    • Primary pollutant of sulfurous grey smog and acid precipitation.
CO (Carbon Monoxide)
  • Main Source: Incomplete combustion of fossil fuels/biomass.
  • Human Impact: Lethal to humans; impairs oxygen transport in the blood.
  • Environmental Impact:
    • Contributes to the formation of tropospheric ozone (O3).
PM (Particulate Matter)
  • Main Source: Combustion of fossil fuels, biomass, construction, and forest fires.
  • Human Impact: Respiratory irritant, affecting lung function and leading to chronic health issues.
  • Environmental Impact: Primary pollutant contributing to photochemical smog formation.
O3 (Tropospheric Ozone)
  • Main Source: Formed via photochemical oxidation of NO2.
  • Human Impact: Respiratory irritant, leading to various health problems.
  • Environmental Impact:
    • Damages plants via stomata, leading to cellular damage.
Pb (Lead)
  • Main Source: Incineration, metal processing, and lead-containing paint in old homes.
  • Human Impact: Neurotoxic, disrupts neurological development; no safe level of exposure.
  • Environmental Impact: Causes soil and water contamination.

Sources and Effects of Lead Exposure

  • Children are High-Risk Group: Lead exposure in children can lead to:

    • Lower IQ, behavioral problems, learning disabilities.
    • Growth impairments and anemia.

  • Sources of Lead in Drinking Water:

    • Copper pipes with lead solder, lead service lines, galvanized pipes, faucets.

Air Pollutants vs Greenhouse Gases

  • Carbon Dioxide (CO2): Regulated by the EPA since 2009, but does not directly lower air quality nor is toxic to breathe.
    • While CO2 is a greenhouse gas, it does not damage human health directly.

Impact of Coal Combustion

  • Releases Various Pollutants: CO2, CO, SOx, NOx, PM, and toxic metals.
  • Health Risks Associated with Coal-Fired Power Plants:
    • Toxic particles (PM2.5) lead to severe respiratory and cardiovascular issues, premature deaths, and chronic diseases.
  • Environmental Effects: Sulfur aerosols block sunlight, contribute to acid rain and can damage ecosystems.

Main Pathways for Nitrogen Oxides (NOx)

  • Formation: NO forms from nitrogen during combustion and converts to NO2.
  • Impacts of NOx: Leads to respiratory and cardiovascular issues, impacts vulnerable populations (elderly, children).

Primary vs Secondary Air Pollutants

  • Primary Pollutants: Emitted directly from sources (e.g., CO, NOx, SO2, PM).
  • Secondary Pollutants: Formed from reactions among primary pollutants (e.g., O3, H2SO4).

Conclusion and Review

Study Goals:
  • Identify sources and effects of primary and secondary air pollutants.
  • Understand the difference between primary and secondary pollutants.
  • Review the overarching impact of the Clean Air Act on air quality and public health.