10. Air Pollutants and their Effects

STB-2: Introduction to Air Pollution – Study Notes

• Enduring Understanding

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

• Learning Objective (STB-2.A)

  • Identify the sources and effects of air pollutants.

• Essential Knowledge (STB-2.A.1–A.5)

  • STB-2.A.1: Coal combustion releases air pollutants including $ext{CO}<em>2, ext{SO}</em>2, toxic metals, and particulates$.
  • STB-2.A.2: Combustion of fossil fuels releases $ext{NO}_x$ into the atmosphere; these contribute to ozone formation, photochemical smog, and conversion to nitric acid in the atmosphere, causing acid rain. Other pollutants from fossil fuel combustion include $ext{CO}, ext{HCs}$, and particulate matter.
  • STB-2.A.3: Air quality can be affected through the release of $ext{SO}_2$ during burning of fossil fuels, mainly diesel.
  • STB-2.A.4: Through the Clean Air Act, the EPA regulated the use of lead, particularly in fuels, which dramatically decreased atmospheric lead levels.
  • STB-2.A.5: Air pollutants can be primary or secondary pollutants.

• Vocabulary (Key Terms to Know)

  • Air pollution, Primary pollutants, Secondary pollutants, Global warming potential, Particulate matter, $ext{CO}<em>2$, $ext{CO}$, $ext{CH}</em>4$, $ext{SO}_2$, NOX, O3, CFC, Montreal Protocol, Pb, Clean Air Act, Asbestos, VOCs, Hydrocarbons

• What is Air Pollution?

  • Air pollution is any substance in the atmosphere above natural concentrations (for this geologic history) that threatens human health or the environment, including climate.
  • It may be created by human activity or natural events (e.g., volcanism).

• Primary vs Secondary Pollutants

  • Primary pollutants: emitted directly from the source. Example: $ext{NO}_x$ emitted from a car’s tailpipe (ICE).
  • Secondary pollutants: created in the atmosphere from chemical reactions of primary pollutants. Example: $ext{NO}_x$ reacting with water to form nitric acid (HNO₃).
  • ICE = Internal Combustion Engine.

• Common Air Pollutants and Their Effects (overview)

  • Particulate Matter (PM)
  • Definition: dust, dirt, soot, smoke, ash, etc.
  • Sources: natural and anthropogenic; any combustion (forest fires, ICEs, coal plants), dirt roads, dust storms, volcanism, etc.
  • Health effects: lung and heart issues; shortness of breath, asthma, heart attacks, cancer; possible early mortality with chronic exposure.
  • Environmental effects: can settle on plants (reducing photosynthesis) and waterways (altering water chemistry).
  • CO₂ (carbon dioxide)
  • Sources: natural and anthropogenic; combustion, cement production, volcanism, respiration.
  • Health effects: typically none; asphyxiation at very high concentrations.
  • Environmental effects: greenhouse gas; major contributor to global warming and climate change.
  • CO (carbon monoxide)
  • Sources: natural and anthropogenic; incomplete combustion (insufficient O₂).
  • Health effects: typically none at low levels; asphyxiation at moderate concentrations (binds hemoglobin with higher affinity than O₂).
  • Environmental effects: indirect climate influence by reacting with OH⁻ to form O₃ (ground-level smog) and CO₂.
  • CH₄ (methane)
  • Sources: natural and anthropogenic; methanogenic bacteria in anaerobic soils, enteric fermentation in animals, rice paddies, thawing permafrost, manure; fossil fuel leaks (oil/gas).
  • Health effects: asphyxiant; possible carcinogen; highly flammable/explosive.
  • Environmental effects: potent short-/long-term greenhouse gas; GWP ≈ 32 over 100 years; ≈ 72 over 20 years.
    • $ext{GWP}<em>{100}( ext{CH}</em>4) \approx 32$
    • $ext{GWP}<em>{20}( ext{CH}</em>4) \approx 72$
  • Methane leaks (contextual data)
  • Natural gas leaks constitute a major anthropogenic CH₄ source (~20% of total CH₄ emissions).
  • Example: 2014 NM oil/gas sector reported > 180,000 metric tons of CH₄ leaks (enough to heat > 168,000 homes for a year).
  • 2015 CA well blowout released > 100,000 tons CH₄.
  • NASA findings: fixing 123 CH₄ leaks in TX could reduce US CH₄ emissions by ~5.5%.
  • SO₂ (sulfur dioxide)
  • Sources: natural and anthropogenic; volcanic activity; burning sulfur-containing fuels (coal, diesel, furnace oil, marine HFO); geothermal plants (small quantities).
  • Health effects: mildly toxic at low concentrations; hazardous at high concentrations.
  • Environmental effects: precursor to $ext{H}<em>2 ext{SO}</em>4$ (sulfuric acid); causes acid deposition (acid rain or dry deposition); can deflect solar radiation and cool the planet; reacts with plant tissues.
  • Reaction: $2 ext{SO}<em>2 + ext{O}</em>2 + 2 ext{H}<em>2 ext{O} ightarrow 2 ext{H}</em>2 ext{SO}_4$
  • NOₓ (nitrogen oxides: NO and NO₂)
  • Sources: natural and anthropogenic; lightning; combustion at high temperatures (coal plants, ICEs); forest fires.
  • Health effects: respiratory issues; asthma; decreased lung function.
  • Environmental effects: primary contributor to smog; reacts to form nitric acid (acid deposition); contributes to ozone formation in the lower troposphere; damages vegetation.
  • N₂O (nitrous oxide)
  • Sources: natural and anthropogenic; denitrifying bacteria/fungi; agriculture (N-fertilizers, animal manure); sewage; biomass combustion; fossil fuel combustion.
  • Uses: anesthetic; aerosol propellant; rocket fuel; boosted vehicle engines.
  • Health effects: few; anesthetic; long-term exposure can cause neurological impairment and DNA damage.
  • Environmental effects: depletes stratospheric ozone via reaction with ozone (O₃); major greenhouse gas (approx. 265× stronger than CO₂ over a 100-year period).
  • O₃ (ozone)
  • Forms as: ground-level (tropospheric) ozone is a pollutant; stratospheric ozone is beneficial (blocks UV).
  • Sources: natural and anthropogenic; formed from O₂ in UV light or electrical activity; secondary pollutant formed when sunlight reacts with hydrocarbons or NOₓ.
  • Health effects: highly corrosive; damages respiratory and circulatory systems.
  • Environmental effects: damages plant/animal tissues; major component of photochemical smog at ground level (troposphere).
  • CFCs/HCFCs/HFCs (fluorinated compounds)
  • Sources: anthropogenic; used as refrigerants (e.g., Freon), propellants, solvents, and other applications.
  • Health effects: limited at typical concentrations; high concentrations can cause dizziness and arrhythmia.
  • Environmental effects: potent greenhouse gases (varying multipliers relative to CO₂, from tens to thousands of times more potent