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Air Pollution. Chapter 20. Sections 20-1 & 20-2. We live at the bottom of a thin layer of gases surrounding the earth Atmosphere The Atmosphere is made up of several layers We live in the troposphere Above the troposphere is the stratosphere. Troposphere 1 st layer of atmosphere

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air pollution

Air Pollution

Chapter 20

sections 20 1 20 2
Sections 20-1 & 20-2
  • We live at the bottom of a thin layer of gases surrounding the earth
    • Atmosphere
  • The Atmosphere is made up of several layers
  • We live in the troposphere
  • Above the troposphere is the stratosphere


  • 1st layer of atmosphere
  • Extends 11 miles above Earth
  • 78% N, 21% O
  • Chemical cycling of nutrients happens here
  • Weather & Climate happen here
  • Water vapor present
  • Stratosphere
  • 2nd layer of atmosphere
  • Extends from 11 – 30 miles above Earth’s surface
  • More ozone (O3) present here
  • Less water vapor

Atmospheric Pressure

    • A measure of the mass per unit of air
  • Pressure of atmosphere increases at the density increases
    • A volume of air with a high density has more gas molecules than air at a lower density (D = m/v)
    • Atmospheric pressure decreases with altitude
      • Ex: At sea level, your body is bombarded with more gas molecules than your body would be at the top of a mountain

Ozone (O3)

    • Found in 2nd layer of atmosphere (stratosphere)
    • Filters our most of the sun’s harmful UV rays
      • Ultraviolet rays – dangerous to organisms, can cause cancer
    • Created when oxygen molecules interact with UV radiation emitted by the sun

Air Pollution

    • Presence of chemicals in the atmosphere in concentrations high enough to affect climate and harm organisms
    • Range from annoying to lethal
  • Sources
    • Majority of air pollution comes from natural sources
    • Ex: dust blowing across the land; organic chemicals released by plants, forest fires, volcanic eruptions, and sea spray

Primary Pollutants

    • Pollutants emitted directly into the troposphere in a potentially harmful form
      • Ex: soot, carbon monoxide (CO)
  • Secondary Pollutants
    • When some primary pollutants react with one another or with the air to form a new pollutant
      • Ex: SO2, H3SO4

U.S. cities typically have higher outdoor pollution levels than rural areas

Due to prevailing winds, the city pollutants are spread to rural areas

Indoor air pollutants come from infiltration of outdoor pollutions into the building


Most people believe CO2 is a pollutant

  • EPA (Environmental Protection Agency)disagrees
    • Too much pressure from oil and coal companies?
    • Repercussions if listed as pollutant by EPA?

CO2 IS a pollutant because:

  • 1) It’s found in high concentrations in the air
    • ANY chemical in high concentrations in the air can become a pollutant
  • 2) We have been increasing CO2 concentrations in the troposphere by burning fossil fuels & clearing CO2-absorbing trees faster than they can grow back
    • No way to get rid of CO2
  • 3) The troposphere is warming & there is considerable evidence that additional CO2 added by humans is the cause
    • Greenhouse gas – warms the Earth
  • UV Rays
  • Air Pollution
sections 20 3 20 4
Sections 20-3 & 20-4
  • Photochemical reaction
  • Any chemical reaction activated by light (photo= light)
  • Ex: Photochemical smog

Photochemical smog

    • A mixture of air pollutants formed by the reaction of nitrogen oxides (NO and NO2 )and volatile organic hydrocarbons
    • Activated by light

Smog pollutants:

  • NO2, NO3 (nitrogen oxides)
  • Ozone
  • Nitric acid
  • Aldehydes
  • Peroxyacyl nitrates (PANs)
  • Sources of smog pollutants:
  • Automobile engines
  • Coal-burning plants
  • Industrial plants
  • Vegetation

Certain trees & plants can contribute to photochemical smog

  • Ex: oak, sweet gums, poplars, kudzu
  • They release volatile organic compounds (VOCs)
    • Ingredient in smog

Trees planted in nonurban areas release their VOCs, which are dispersed into the atmosphere

    • They do not make a significant contribution to the formation of photochemical smog
  • Trees planted in / near urban areas with high levels of NOx (nitrogen oxides) and sunlight, will create high levels of VOCs
  • Environmentalists’ view: widespread planting of trees in urban areas BUT only those who emit low VOCs

Industrial smog

    • A mixture of sulfur dioxide, droplets of sulfuric acid, and a variety of particles emitted by burning coal and oil
    • When burned, carbon in coal and oil is converted to CO2 and CO
      • Some of this ends up in atmosphere as ingredient of smog

Industrial smog

    • Also known as: gray-air-smog
  • Not a big problem in developed countries
    • Good pollution control when coal & oil are burned
  • It IS a big problem in industrialized urban areas of:
    • China, India, Ukraine, Slovakia, Poland, Hungary, and Czech Republic

Factors that decrease outdoor air pollution:

    • Precipitation
      • Rain & snow help to cleanse the air, lowering pollution
    • Sea Spray
      • Can wash out particulates & water-soluble pollutants from air that flows from land onto the oceans
    • Wind
      • Can sweep pollutants away or dilute them
      • Pollutants are blown somewhere else
      • Can be deposited onto surface waters, soil, buildings

Factors that increase outdoor air pollution:

    • Urban buildings
      • Slow wind speed
      • Reduce dilution / removal of pollutants
    • Hills and Mountains
      • Reduced the flow of air in valleys below them
        • Allows pollutants to build up at ground level
    • High temperatures
      • Promote chemical reactions leading to photochemical smog
    • Grasshopper effect
      • Transfers air pollutants from tropical / temperate areas to the earth’s poles
      • Reason for high levels of pollutants, decreasing ozone in poles
grasshopper effect
Grasshopper Effect

Keep in mind that the warm air rises in the temperate / tropical areas and will condense once it reaches the colder temperatures (earth’s poles).


Temperature Inversion

    • Occurs when cool, dense air is trapped under a warm, less dense air
    • These two air masses do not mix
    • As a result, pollutants in the air can be concentrated in the lower layer of cool air (closest to the earth)
case study s asia s brown cloud
Case Study: S. Asia’s Brown Cloud

Asian brown cloud (industrial smog)

2 miles thick

Caused by huge emissions of ash, smoke, dust, acidic compounds (from burning coal), burning trees (to plant crops), dust blowing from desserts

As the cloud travels it picks up many pollutants

case study s asia s brown cloud1
Case Study: S. Asia’s Brown Cloud
  • Impacts:
  • Effects the amount of solar energy hitting earth
    • Impacts of crop production
    • Damage trees
    • Can kill organisms in lakes
  • Illnesses & premature deaths
    • Respiratory diseases
  • Particles in cloud are causing climate change
    • Changes temperature pattern, rainfall shifts
    • Can effect El Nino (which could affect North & South America)

South Asia’s

Brown Cloud


Acid deposition / acid rain:

    • Mixture of wet deposition & dry deposition
    • Wet deposition: acid rain, snow, fog, cloud vapor
      • pH is less than 5.6
    • Dry deposition: acidic particles
  • Composed of:
    • Sulfur dioxide (SO2)
    • Nitrogen oxides (NO2 and NO)
    • Particulates

Some soils contain chemicals which buffer acidic deposition / rain:

    • Calcium carbonate (CaCO3)
    • Limestone
  • Chemicals neutralize acids
    • Bring pH closer to 7

Harmful effects of acid deposition / rain:

    • Human respiratory diseases
      • Bronchitis, asthma
    • Can leach toxic chemicals into drinking water
      • Lead, copper
    • Damages statues, monuments, buildings, metals
      • Including car finishes, eats away / dissolve certain types of rock
    • Can kill aquatic life if pH drops too low
    • Acid shock
      • Damage to aquatic life due to runoff of large amounts of highly acidic water

Effects of acid rain on plants and soil:

    • Can deplete soil nutrients
      • Calcium and Magnesium
    • Release toxic ions into the soil
    • Weaken plants
      • If pH of soil drops below 5.1
    • Calcium deficiencies in plants can be passed to the organisms who eat them
      • Ex: birds eating these plants could have problems with egg production (shell made of calcium)

Synergistic effect

    • When the interaction of two or more factors’ combined effect is greater than the sum of their separate effects

Clean Air Act

    • Has helped reduce some of the harmful impacts of acid deposition

Solutions to acid deposition:

  • Prevention (BEST solutions)
    • Improve energy efficiency
    • Reduce coal use or burn low-sulfur coal
    • Increase natural gas use and renewable energy
    • Remove SO2 particulates and NOx from smokestack gases
    • Fees for SO2 emissions
  • Cleanup
    • Add lime or phosphate fertilizer to neutralize acidified lakes

Controlling acid deposition / rain is a challenge:

    • The people who cause acid rain and the people or ecosystems affected by it are quite distant
    • Countries with large supplies of coal (which produces acid rain) want to use coal for energy
    • Coal-burning power plants say it’s too costly to install equipment to reduce harmful emissions
  • Environmentalists idea- Use alternative energy sources (wind turbines, natural gas)

Cleanup of acid rain in lakes & soil

    • Add limestone (or lime) to neutralize
    • Called “liming”
    • Problems:
      • Expensive
      • Needs to be repeated annually (temporary fix)
      • Can kill some aquatic plants, plankton, wetland plants
    • Possible solution:
      • Add phosphate fertilizer to neutralize
      • Effectiveness still being evaluated
video clips
Video Clips

Thermal Inversion demonstration

Thermal Inversion in the real world

Asia’s Pollution Super Cloud

Coal combustion & Acid Rain

hippocampus videos http www hippocampus org
Hippocampus Videos
  • Go to hippocampus link
  • On the left-hand side of the screen click “Earth Science”
  • Click “Environmental Science for AP”
  • Scroll down the middle of the page
  • Watch the following videos:
    • Earth’s atmosphere
    • Ozone
    • Photochemical smog
    • Air pollution