Chapter 17

• Atmosphere

  Thin layers of gases which envelope the Earth
• Troposphere


  • Layer closest to Earth's surface
  • Contains 75% of atmosphere's mass
  • Region that supports life
  • 78% Nitrogen, 21% O2, 0.04% CO2
  • Weather occurs in this layer
  • Temperature decreases as away from the earth's surface
• Stratosphere


  • Second closest atmospheric layer to Earth's surface
  • Tropopause denotes boundary
  • Ozone layer found here
  • O2 + UV light -> O3 (Ozone)
  • Acts as a global "sunscreen" as it absorbs energy from UV light before it strikes the surface of the Earth
• Aerosols


  • Tiny solid and liquid particles suspended in air (clouds & fog)
  • Size of particle determines if it can be suspended in the atmosphere
• Volatile organic compounds (VOCs)


  • Chemicals that vaporize into air
  • Can be natural or anthropogenic in origin
• Categories of Pollutants


  • Primary Pollutants (harmful chemicals emitted directly into the atmosphere)
  • Secondary Pollutants (harmful chemicals that form via chemical modification of primary pollutants)
• Primary Pollutants


  • Sulfur Dioxide (SO2)
  • Carbon Monoxide (CO)
  • Carbon Dioxide (CO2)
  • Nitrogen Oxides (NO & NO2)
• Secondary Pollutants


  • Sulfuric Acid (H2SO4)
  • Nitric Acid (HNO3)
  • Ozone (O3)
• Natural processes, some worsened by human activity, can also pollute the air
• Fires occur naturally, but are worsened by human encroachment into fire-prone ecosystems and the suppression of fires in areas where it is part of the natural ecology
• Volcanic eruptions release particulate matter and sulfur dioxide into the stratosphere
• Short-term effects of volcanic eruptions

  • Grounding planes, damaging car engines, and causing respiratory illnesses
• Long-term effects of volcanic eruptions

  • Global cooling can occur if sulfur dioxide reacts with water and oxygen to form aerosols that block sunlight in the stratosphere
• Sources of Pollutants


  • Stationary sources (power plants & factories)
  • Mobile sources (motor vehicles)
• Point sources


  Stationary, localized sources (smoke stacks)
• Non-point sources


  Numerous sources that produce a relatively small amount (cars, residential fireplaces)
• Industrial Smog


  • Gray sooty smog composed of particles and SO2
  • Typically worse in winter months
• Photochemical Smog


  • Caused by VOCs, NOx reacting with sunlight
  • Main components are ozone, PAN's
• Industrial Smog - Great London Fog 1952 lasted 5 days and killed 12,000 people
• Photochemical Smog formation


  VOCs + NO2 + heat + sunlight -> ground level ozone
• Photochemical Smog


  • Secondary pollutants, such as Ozone, act as strong oxidants that are reactive to living tissues
  • Irritate eyes, respiratory tracts of animals
  • Damage plants as well
• Warm cities


  More susceptible to Photochemical Smog
• Colder cities


  More susceptible to industrial smog in winter months due to heating of buildings
• Inversion


  Occurs when cooler air is trapped below a cap of warmer air, trapping polluted air near the surface
• Rainfall has a lower pH (is more acidic) near cities and industrial centers
• Nutritional elements availability within soil varies with pH
• Sulfur dioxide and nitrogen oxides interact with the air to form nitric & sulfuric acids
• Criteria Pollutants (CLEAN AIR ACT)

  • Sulfur Dioxides (SO2)
  • Nitrogen Dioxides (NO2)
  • Ozone (Tropospheric)
  • Carbon Monoxide (CO)
  • Particulate Matter (PM)
  • Lead
  • VOC'S (volatile organic compounds)
• While the air in most urban areas still violates at least one ambient air quality standard, air quality has shown great improvement since 1985
• Mercury Cycle


  • Mercury is neuro-, nephro-, and immunotoxic
  • Ingestion can effect the nervous, digestive and immune systems, lungs and kidneys
• Mercury levels in different parts of the ecosystem

  • Water: 0.000003 ppm, or 3 ppt
  • Small fish (minnows): 0.5 ppm
  • Zooplankton: 0.04 ppm
  • Fish-eating birds (ospreys): 25 ppm
  • Large fish (needle fish): 2 ppm
• Bioaccumulation and biomagnification


  Increase in concentration of a substance, such as a toxic chemical, in the tissues of organisms at higher levels in a food chain
• Electrostatic precipitator


  • Removes particles from a flowing gas (such as air) using the force of an induced electrostatic charge
  • Charged particles follow the induced electrostatic field
• Scrubber


  • Uses liquid to wash unwanted pollutants from a gas stream
  • Efficiency of removal increases with residence time or surface area of liquid
  • Can remove gas, particulate, and thermal pollutants
• Vapor recovery systems minimize escape of volatile organic compounds (VOCs)
• Catalytic converters


  • Phased in for new vehicles
  • Regular emissions inspections implemented
  • Alternatives to cars, including public transportation, ride-sharing, and bicycling, were also promoted
  • By 2010–2015, most pollutants had been reduced by more than 75%
• Air Quality Legislation


  • 1963 First Air Quality Act
  • 1970 First Clean Air Act (Nixon)
  • 1977 amendments
  • 1990 major amendments to Clean Air Act; introduced some market-based instruments
  • 1997 - new standards for ozone and particulates