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5.7 Urban Air Pollution

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Sub-subtopics

5.7.1 State the source and outline the effect of tropospheric ozone.

5.7.2 Outline the formation of photochemical smog.

5.7.3 Describe and evaluate pollution management strategies for urban air pollution.

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5.7.1 Combustion

Sources?

  • Rutherford p.277
  • Davis&Nagle p.252
    • Mexico City

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4-stroke engine

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5.7.1 One-Box Model

  • Simplified model for gas X
  • Concept of lifetime (called residence time when a physical process)

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5.7.1 Tropospheric Ozone

Ozone (~10%)

  • toxic gas
    • <1850 10-15ppb
    • now, 30ppb
  • oxidizing agent
    • fabrics
    • rubber
  • damages crops (>40ppb)
    • degrades chlorophyll
  • irritates eyes
  • causes breathing difficulty

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5.7.2 Urban Air Pollution

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5.7.2 Particulates

Burning organic/fossil fuels

  • Poorly maintained diesel engines
  • PM10 (<10µm diameter)
    • respiratory filters do not filter them out
      • nose hair
      • bronchial passages
    • enter body and stay
      • asthma
      • lung cancer
      • respiratory problems
      • death
    • crops covered
      • reduce productivity

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5.7.2 Photochemical Smog

Smog = smoke + fog

  • Mixture of ~100 different primary and secondary pollutants
    • Primary pollutants: emitted directly, e.g., NOx and hydrocarbons
    • Secondary pollutants: produced by primary & reaction, e.g., VOCs and PANs
  • Contributing factors:
    • local topography
    • climate
    • population density
    • fossil fuel use
    • e.g., large cities in valleys

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5.7.2 Photochemical Smog

Summer

  • rush hour traffic
  • ozone, NOx, gaseous hydrocarbons + energy (sunlight)
  • reactions form
    • Volatile Organic Compounds (VOCs)
    • Peroxyacyl nitrates (PANs)
    • Ozone
    • Aldehydes
    • CO
    • NOx
    • NO2 is a brown gas
  • Los Angeles-type
  • Worse in the afternoon
    • Why?

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5.7.2 Photochemical Smog

Winter

  • heating
  • vehicles operate less efficiently
    • more CO & hydrocarbons released
  • thermal inversion
    • cold air sinks
  • high levels of SO2, and other primary pollutants
  • Prague-type smog

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History of Deadly Smogs

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5.7.3 Management Strategies

Automobiles

  • Catalytic converters
  • Hybrid
  • Electric
  • Hydrogen
  • Fuel cell
  • Stopping days
  • Engine maintenance standards
  • Change gasoline quality
  • Carpooling
  • Fuel economy

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5.7.3 Management Strategies

CCS - Carbon Capture & Storage (Sequestration)

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