Outdoor Air Pollution

• Characteristics of Earth's Atmosphere

  • Thin layer of gases that surrounds Earth
  • Absorbs radiation and moderates climate
  • Transports and recycles water, nutrients and contaminants
  • Human activity is changing the amounts of some gases
• Layers of Atmosphere


  • Tropospheric ozone ("bad")
  • Stratospheric ozone ("good")
  • Thermosphere
  • Mesosphere
• Composition of Atmosphere
• Primary Pollutants


  Directly harmful and can react to form harmful substances (soot, carbon dioxide)
• Secondary Pollutants


  Form when primary pollutants interact or react with constituents or components of atmosphere (e.g. tropospheric (ground-level) ozone and sulfuric acid)
• Sources of Outdoor Air Pollution

  • Mobile sources
  • Stationary sources
• Point Sources


  Specific spots where large quantities of pollutants are discharged (power plants and factories)
• Non-point Sources


  More diffuse, consisting of many small sources (automobiles)
• Natural Sources of Outdoor Air Pollution

  • Dust Storms
  • Volcanoes
  • Natural Fires
• Dust Storms: Millions of tons of dust are carried long distances by winds due to unsustainable farming / grazing that cause erosion / desertification
• Volcanoes release large quantities of particulate matter, sulfur dioxide and other gases into atmosphere
• Natural Fires pollute atmosphere with soot and gases caused by human activities (e.g. clearing forests, harsh droughts, climate change)
• Criteria Air Contaminants for Outdoor Air

  • Sulfur dioxide (SO2)
  • Nitrogen dioxide (NO2)
  • Ammonia (NH3)
  • Particulate matter (PM)
  • Lead (Pb)
  • Carbon monoxide (CO)
  • Tropospheric (ground-level) ozone (O3)
  • Volatile organic compounds (VOC or VOX)
• Sulfur dioxide (SO2)


  Colorless gas with a strong odor, from coal emissions from electricity generation and industry - can form acid precipitation
• Nitrogen Gases


  Nitrogen dioxide (NO2) = very reactive, foul smelling reddish brown gas

  Nitrogen oxides (NOx) = nitrogen and oxygen react at high temperatures, from vehicle engines, industrial combustion, electrical utilities - smog / acid precipitation
• Ammonia (NH3)


  From agriculture
• Particulate Matter


  Solid or liquid particles suspended in the atmosphere, primary pollutants: dust and soot, secondary pollutants: sulfates and nitrates, damages respiratory tissue when inhaled, most is wind-blown dust
• Lead


  Particulate pollutant added to gas and used in industrial metal smelting, bioaccumulates and causes nervous system malfunction, banned in gasoline in developed, but not in developing countries
• Carbon Monoxide (CO)


  Colorless, odorless gas, produced primarily by incomplete combustion of fuel, risk to humans / animals (even in small concentrations)
• Tropospheric Ozone (O3)


  Colorless gas with strong odor, secondary pollutant, results from interactions of sunlight, heat, nitrogen oxides, and volatile carbons, major component of smog, poses a health risk as a result of its instability
• Volatile Organic Compounds (VOCs or VOXs)


  Most diverse group of air pollutants, found outside (from vehicle exhaust)
• Types of Outdoor Air Pollution

  • Industrial (gray air) smog
  • Photochemical smog
• Industrial (gray air) smog is from industries burning coal or oil, reduced by government regulations in developed countries, industrializing countries still face significant health risks
• Photochemical smog is produced by light-driven reactions of primary pollutants and normal atmospheric compounds (from vehicles)
• Outdoor pollution is increasing, Factories and power plants do not control emissions, Citizens burn traditional fuels (wood and charcoal), China has world's worst air pollution, 80% of Chinese cities have emissions above safety threshold, Asian brown cloud = a 2-mile thick layer of pollution that reduces sunlight, affects climate, decreases productivity, kills thousands annually
• Total emissions of six monitored pollutants have declined despite increased population, energy consumption, miles traveled, and gross domestic product