Clean Air Act (College Board AP® Environmental Science): Study Guide

Clean Air Act (CAA)

Background

• Enacted in response to growing concerns about air pollution and public health, particularly in urban and industrial areas

  • 1940s–60s: Major cities like Los Angeles and Pittsburgh experienced extreme smog events

  • Scientific links were made between pollutants like lead, sulfur dioxide (SO₂), and particulates, and serious health effects

• The legislation aimed to:

  • Reduce pollutants harmful to human health and the environment

  • Set national air quality standards for six major pollutants

  • Empower the Environmental Protection Agency (EPA) to enforce these regulations

Key dates

• 1963: Original Clean Air Act passed — first federal legislation to control air pollution

• 1970: Major amendments established the EPA and national standards for air quality

• 1990: Further amendments addressed acid rain, ozone depletion, and toxic air pollutants

How the Clean Air Act relates to the environment

• Targets six criteria air pollutants:

  • Carbon monoxide (CO)

  • Lead (Pb)

  • Nitrogen oxides (NOx)

  • Ground-level ozone (O₃)

  • Sulfur dioxide (SO₂)

  • Particulate matter (PM)

• These pollutants are linked to human health impacts, ecosystem damage, and climate change

• Examples of environmental connections:

  • Reduced lead in air due to CAA restrictions on leaded gasoline → improved public and ecosystem health

  • Reduced SO₂ emissions have led to less acid rain, helping forests and aquatic systems

  • Regulation of nitrogen oxides (NOx) contributes to less photochemical smog and ground-level ozone

• Clean Air Act implementation strategies include

  • Use of catalytic converters in vehicles

  • Installation of scrubbers in industrial smokestacks

  • Promotion of alternative fuels and clean energy sources

Evaluation

• Successes:

  • Dramatic decrease in key pollutants, even as population and energy use increased

  • U.S. air quality has significantly improved since the 1970s

  • Linked to public health benefits: fewer respiratory illnesses, asthma attacks, and premature deaths

• Challenges:

  • Some pollutants (e.g. ground-level ozone, PM2.5) remain hard to control in urban areas

  • Enforcement can be inconsistent across states

  • Emerging pollutants like microplastics and indoor air toxins not covered by the Act

  • Needs updates to address climate change-related emissions, like methane and CO₂, more directly