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  • William P. Cunningham University of Minnesota
  • Mary Ann Cunningham Vassar College
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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  • Chapter 16
  • Lecture Outline*

Air Pollution


The Air Around Us

  • Approximately 147 million metric tons of air pollution are released annually into the atmosphere in the U.S. by human activities.
    • Worldwide emissions total around 2 billion metric tons.
  • Developed countries have been improving air quality, while air quality in developing world is getting worse.

Natural Sources of Air Pollution

  • Volcanoes - Ash and acidic components
  • Sea Spray - Sulfur
  • Vegetation - Volatile organic compounds
  • Pollen, spores, viruses, bacteria
  • Dust storms
  • Bacterial metabolism is responsible for 2/3 of methane in the air.
  • Forest fires

Human-Caused Air Pollution

  • Primary Pollutants - released directly from the source
  • Secondary Pollutants - modified to a hazardous form after entering the air and mixing with other environmental components
    • Fugitive Emissions - do not go through smokestack
      • Dust from strip mining, rock crushing, building construction/destruction

Conventional Pollutants

  • U.S. Clean Air Act designated seven major (conventional or criteria pollutants) for which maximum ambient air levels are mandated.
    • Sulfur Dioxide
    • Nitrogen Oxides
    • Carbon Monoxide
    • Particulates
    • Hydrocarbons
    • Photochemical Oxidants
    • Lead

Sources of Some Criteria Pollutants

Conventional Pollutants

  • Sulfur Compounds
    • Natural sources of sulfur in the atmosphere include evaporation from sea spray, volcanic fumes, and organic compounds.
    • Predominant form of anthropogenic sulfur is sulfur-dioxide from fossil-fuel combustion (coal and oil) and smelting of sulfide ores.
      • Sulfur dioxide is a corrosive gas which reacts with water vapor in the air to cause acid rain.

Conventional Pollutants

  • Nitrogen Compounds
    • Nitrogen oxides are reactive gases formed when nitrogen is heated above 650oC in the presence of oxygen, or when nitrogen compounds are oxidized by bacteria.
      • Nitric oxide is further oxidized to give nitrogen dioxide, the reddish brown gas in smog.
      • Nitrogen oxides combine with water to make the nitric acid found in acid rain (along with sulfuric acid discussed earlier).

Nitrogen Compounds

  • Excess nitrogen is causing fertilization and eutrophication of inland waters and coastal seas. It also encourages the growth of weeds that crowd out native species. Humans are responsible for 60% of emissions.

Conventional Pollutants

  • Carbon Oxides
    • Predominant form of carbon in the air is carbon dioxide.
      • Increasing levels due to use of fossil fuels
        • Cause of global warming
    • Carbon monoxide is a colorless, odorless, toxic gas produced by incomplete fuel combustion.

Conventional Pollutants

  • Particulate Matter
    • Aerosol
      • solid particles or liquid droplets suspended in a gaseous medium
      • atmospheric aerosols are usually called particulate material
      • includes ash, soot, lint, smoke, pollen, spores, etc.
    • Aerosols reduce visibility.
    • When smaller than 2.5 micrometers, they enter lungs and cause damage.
      • Asbestos and cigarette smoke cause cancer.

Conventional Pollutants-Particulate Matter

  • Soil erosion causes dust and sand storms that put particulate matter into air.
    • Dust can travel thousands of km. Dust from the Sahara regularly ends up in Miami, Florida. And dust from China’s Gobi desert ends up in Seattle.
      • Some benefits to this movement of particulate matter as nutrients from Africa fertilize the Amazon basin

Dust Storm

Conventional Pollutants-Particulate Matter

  • Human health suffers from exposure
    • Cities with high particulates have a higher death rate
    • Dust also carries bacteria, viruses, fungi, pesticides, herbicides and heavy metals
      • Outbreak of foot- and- mouth disease in Britain linked to dust from North Africa
      • Recent discovery of nanobacteria in dust
    • Primary source of allergies and asthma

Conventional Pollutants

  • Metals
    • Many toxic metals occur as trace elements in fuel, especially coal
      • Lead- 2/3 of all metallic air pollution
        • Lead is a neurotoxin; banning lead from gas was one of most successful pollution controls in American history.
        • Since ban, children’s average blood levels have dropped and average IQ has risen

Conventional Pollutants-Metals

    • Mercury
      • Dangerous neurotoxin
      • Minamata, Japan disaster
      • In 2007, all sampled rivers in 12 western states were contaminated
      • 45 states have warnings about local fish and pregnant women and children should limit consumption of tuna, swordfish, marlin, lobster
      • 300,000 to 600,000 children in U.S. exposed in the womb each year, resulting in diminished intelligence

Conventional Pollutants

  • Other toxic metals
    • Nickel, beryllium, cadmium, arsenic…
  • Halogens (Fluorine, Chlorine, Bromine)
    • CFCs (chlorofluorocarbons) release chlorine and fluorine in the stratosphere, which deplete ozone layer.
      • Ozone layer protects life against UV radiation
      • CFCs banned in developed countries but still used elsewhere in propellants and refrigerators

Conventional Pollutants

  • Volatile Organic Compounds
    • Organic chemicals
      • Generally oxidized to CO and CO2
      • Plants are largest source.
  • Photochemical Oxidants
    • Products of secondary atmospheric reactions driven by solar energy.
      • Ozone formed. In stratosphere, it protects against UV radiation, but in ambient air it contributes to smog and damages lungs.

Air Toxins

  • Hazardous Air Pollutants
    • Require special reporting and management as they remain in ecosystems for a long period of time, and tend to accumulate in animal tissues.
      • Include carcinogens, neurotoxins, endocrine disrupters
    • Toxic Release Inventory
      • Requires manufacturers to report on toxin release and waste management
    • Most HAP are decreasing but mercury and dioxins (from plastics) are increasing
  • More than 100 million Americans live in areas where cancer rate is 10X normal standard.

Unconventional Pollutants

  • Aesthetic Degradation
    • Noise, odor, light pollution
      • Reduce quality of life.
      • Light pollution prevents us from seeing stars and is a serious problem for astronomers.

Indoor Air Pollution

  • EPA found indoor concentrations of toxic air pollutants are often higher than outdoor.
    • People generally spend more time indoors.
    • Smoking is the most important air pollutant in the U.S.
      • 400,000 die annually from diseases related to smoking. This is 20% of all mortality.
        • Associated costs are estimated at $100 billion annually.
    • Chloroform, benzene and other chemicals can be found in homes at concentrations that would be illegal in workplace.

Indoor Air Pollution

  • Less Developed Countries also suffer from indoor air pollution.
    • Organic fuels make up majority of household energy.
      • Often burned in smoky, poorly ventilated heating and cooking fires.

Climate and Topography

  • Inversions
    • Temperature inversions occur when a stable layer of warm air overlays cooler air, reversing the normal temperature decline with increasing height, and preventing convection currents from dispersing pollutants.
      • Cold front slides under warm air mass.
      • Cool air subsides down slope.
        • Rapid nighttime cooling in a basin

Dust Domes and Heat Islands

  • Sparse vegetation and large amounts of concrete and glass create warm, stable air masses, heat islands, over large cities.
    • Concentrates pollutants in a “dust dome”.
      • Rural areas downwind from major industrial areas often have significantly decreased visibility and increased rainfall.

Long-Range Transport

  • Fine aerosols can be carried great distances by the wind.
    • 3 km toxic cloud covers India for most of year, causing 2 million deaths/yr.
      • Cloud may also be disrupting monsoon rains on which harvests in South Asia depend
      • When cloud drifts over Indian Ocean at end of monsoon season, it may be changing El Nino patterns

Long-Range Transport

  • Increasingly, sensitive monitoring equipment has begun to reveal industrial contaminants in places usually considered among the cleanest in the world (e.g. Antarctica).
    • Grasshopper transport - volatile compounds evaporate from warm areas; travel to poles where they condense and precipitate. Contaminants bioaccumulate in food webs. Whales, polar bears, sharks have dangerously high levels of contaminants.

Long-Range Transport

Stratospheric Ozone

  • Discovered in 1985 that stratospheric ozone levels over South Pole were dropping rapidly during September and October.
    • Occurring since at least 1960
    • Chlorofluorocarbons are the cause.
  • At ground-level, ozone is a pollutant, but in the stratosphere it screens UV radiation.
    • A 1% decrease in ozone could result in a million extra human skin cancers per year worldwide.
    • Decreased agricultural production and reduced plankton in the ocean, the basis of food chain

Ozone Hole Over Antarctic

Stratospheric Ozone

  • Circumpolar vortex isolates Antarctic air and allows stratospheric temperatures to drop and create ice crystals at high altitudes.
    • Absorb ozone and chlorine molecules.
      • When sun returns in the spring, energy liberates the chlorine allowing it to destroy ozone
      • Persist for decades
      • Ozone hole has grown almost every year. Now larger than North America
      • Hole has begun to form over Arctic, too

Montreal Protocol

  • Montreal Protocol (1987) phased out use of CFCs. HCFCs were substituted, which release less chlorine.
  • Very successful - CFCs cut by 95%
  • In 1995, Rowland, Molina and Crutzen shared Nobel Prize for work on ozone problem.

Effects of Air Pollution

  • Human Health
    • WHO estimates each year 5-6 million people die prematurely from illnesses related to air pollution.
      • Likelihood of suffering ill health is related to intensity and duration of exposure.
        • As much as a 5 to 10 year decrease in life expectancy if you live in worst parts of Los Angeles

Effects of Air Pollution

  • PM2.5 - particulates less than 2.5 micron in diameter are particularly risky and have been linked with heart attack, asthma, lung cancer and abnormal fetal development.
  • New rules will remove particulates from diesel engines and power plants.
  • Most air pollutants are inhaled, but some can be directly absorbed through the skin or ingested in food and water.

Human Health

  • Bronchitis
    • Persistent inflammation of airways in the lung that causes mucus build-up and muscle spasms constricting airways.
      • Can lead to emphysema - irreversible chronic obstructive lung disease in which airways become permanently constricted and alveoli are damaged or destroyed.
      • In the U.S. half of all lungs examined at autopsy show alveolar deterioration.

Normal vs. Constricted Airways

Plants are Susceptible to Pollution

  • Chemical pollutants can directly damage plants or can cause indirect damage by reducing yields.
    • Certain environmental factors have synergistic effects in which the injury caused by the combination is more than the sum of the individual exposures.
      • Pollutant levels too low to cause visible effects may still be damaging.

Soybean Leaves Damaged by Sulfur Dioxide

Acid Deposition

  • Acid precipitation - deposition of wet acidic solutions or dry acidic particles from the air
    • Unpolluted rain generally has pH of 5.6.
      • Carbonic acid from atmospheric CO2
    • H2SO4 and HNO3 from industrial and automobile emissions are cause of acid precipitation.
    • Aquatic effects are severe, as pH of 5 in freshwater lakes disrupts animal reproduction and kills plants, insects and invertebrates. Below pH 5, adult fish die.

Acid Precipitation

Acid Deposition

  • Forest Damage
    • Air pollution and depositions of atmospheric acids are believed to be important causes of catastrophic forest destruction in Europe, North America.
  • Buildings and Monuments
    • Limestone and marble are destroyed by air pollution at an alarming rate.
    • Corroding steel in reinforced concrete weakens buildings, roads, and bridges.
  • Smog and Haze reduce visibility.

Air Pollution Control

  • Reducing Production
    • Particulate Removal
      • Remove particles physically by trapping them in a porous mesh which allows air to pass through but holds back solids.
      • Electrostatic Precipitators - fly ash particles pick up electrostatic charge as they pass between large electrodes in waste stream, and accumulate on collecting plate

Electrostatic Precipitator

Air Pollution Control

    • Sulfur Removal
      • Switch from soft coal with a high sulfur content to low sulfur coal.
      • Change to another fuel (natural gas).
    • Nitrogen Oxides
      • Best method is to prevent creation
        • Staged Burners
        • Selective Catalysts
    • Hydrocarbon Control
      • Use closed systems to prevent escape of fugitive emissions.

Clean Air Legislation

  • Clean Air Act (1963) - First national air pollution control
  • Clean Air Act (1970) rewrote original.
    • Identified critical pollutants.
    • Established ambient air quality standards.
      • Primary Standards - human health
      • Secondary Standards - materials, crops, visibility, climate and comfort

Clean Air Legislation

    • Source review in 1977 allowed old plants to be grandfathered in, but required new equipment to meet air pollution standards.
      • Result was that companies kept old facilities operating in order to avoid pollution controls
      • Thirty years later, these old plants (often expanded in size) continue to be among biggest contributors to smog/acid rain.
      • Clinton attempted to force utilities to install new equipment; Bush abandoned this in favor of voluntary controls and air pollution allowances.

Cap and Trade

  • Cap and Trade programs set maximum amounts for pollutants, but let facilities facing costly cleanups pay others with lower costs to reduce emissions on their behalf.
    • Has worked well for sulfur dioxide
    • However, it permits local hot spots where high polluters continue to pollute because they are paying someone somewhere else to reduce pollution.

Current Conditions and Future Prospects

  • Air pollution in the US has improved dramatically in the last decade.
  • For the 23 largest cities in the US, the number of days per year with hazardous levels of pollutants has declined 93%.
  • Lead, sulfur dioxide, carbon monoxide, and ozone have all declined significantly.
  • The only pollutants that have not shown significant declines are particulates and Nitrogen Oxides.
  • 80% of U.S. cities now meet National Ambient Air Quality Standards.

Air Pollution Trends in the U.S.

Air Pollution in Developing Countries

    • Mexico City
      • Pollution levels exceed WHO health standards 350 days per year.
      • More than half of children have lead levels high enough to lower intelligence.
    • China’s 400,000 factories have no air pollution controls.
    • Former Soviet Union has serious problems as well.

Signs of Hope

  • Sweden and West Germany cut their sulfur emission by two-thirds between 1970 and 1985.
  • Australia and Switzerland even regulate motorcycle emissions.
  • Delhi, India was once one of world’s most polluted cities. Breathing the air equal to smoking 2 packs a day. After instituting air pollution controls, air is dramatically cleaner.

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