Air pollution
• 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
• Natural fires - smoke
• Volcanoes - ash and acidic components
• Sea spray - sulfur
• Vegetation - volatile organic compounds
• Bacterial metabolism - methane
• Pollen
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 human-activities
Conventional pollutants
• U.S. Clean Air Act designated seven major (conventional or criteria) pollutants
for which maximum ambient air levels are mandated
• Most serious threat to human health
Conventional Pollutants
• Sulfur compounds
 Two thirds of total sulfur in the atmosphere is from human activity
 Predominant form of anthropogenic sulfur is sulfur-dioxide from fossil-fuel
combustion
 Colorless corrosive gas that directly damages both plants and animals
 Can react with water to form acid rain
 Second only to smoking as cause of air pollution-related health damage
Conventional pollutants
• Carbon oxides
 Predominant form of carbon in the air is carbon dioxide
 Increasing levels due to human activities.
 Carbon monoxide is a colorless, odorless, toxic gas produced by
incomplete fuel combustion
Conventional pollutants
• Particulate matter
 Atmospheric aerosols (solid or liquid)
 Aerosol is any system of solid particles or liquid droplets suspended in a
gaseous medium
 Respirable particles smaller than 2.5 micrometers are among most
dangerous
 Diesel fumes dangerous
 Reduces visibility and leaves dirty deposits on surfaces
Conventional pollutants
• Volatile organic compounds
 Organic chemicals
 Generally oxidized to CO and CO2
 Plants are largest source
 Released by humans by use of synthetic organic chemicals
Conventional pollutants
• Nitrogen compounds
 Also called NOx
 60 % of NO emissions are anthropogenic
 Produced by fuel combustion in transportation and electric power
generation
 Excess nitrogen causing eutrophication in water bodies
 Low oxygen caused by decomposition of organic material
 Encourages growth of weedy plant species
Conventional pollutants
• Photochemical oxidants
 Products of secondary atmospheric reactions driven by solar energy
 Ozone formed by splitting nitrogen dioxide
Conventional pollutants
• Metals
 Many toxic metals occur as trace elements in fuel
 Since leaded gasoline was banned, children’s average lead levels have
dropped 90% and IQs have risen by 3 points
 Mercury
 Released from coal burning power plants and waste incinerators
 Bioaccumulation in aquatic ecosystems
 Nickel, beryllium, cadmium, arsenic
 Halogens (Fluorine, Chlorine, Bromine)
 CFC’s
Major Pollutants
 Unconventional Pollutants
 Compounds produced in less volume than conventional pollutants, but
are especially toxic or hazardous
 Aesthetic Degradation
 Reduce quality of life
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 a disease related to smoking
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
• Topography, climate and physical processes play important roles in transport,
concentration, dispersal and removal of air pollutants
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
 Usually created by rapid nighttime cooling in a basin where air
movement is restricted
Dust domes and heat islands
• Sparse vegetation and large amounts of concrete and glass create warm,
stable air masses, heat islands, over large cities
• Pollutants are concentrated 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
Long-range transport
• Increasingly, sensitive monitoring equipment has begun to reveal industrial
contaminants in places usually considered among the cleanest in the world
 Contaminants evaporate from warmer areas and condense and precipitate
in cooler areas
Stratospheric ozone
• Discovered in 1985 that stratospheric ozone levels were dropping rapidly
during September and October
 Occurring since at least 1960
• At ground-level, ozone is a pollutant, but in the stratosphere it screens UV
radiation
Stratospheric ozone depletion
• CFCs believed to be main culprit
 Persist for decades
 Ban established in 1987
 Models show that stratospheric ozone levels could reach normal levels by
2040
Effects of air pollution
• Human health
 EPA estimates each year 50,000 people die prematurely from illnesses
related to air pollution in US
 WHO estimates 5-6 million die prematurely from illnesses related to air
pollution
 Likelihood of suffering ill health is related to intensity and duration of
exposure
 Inhalation is the most common route, but absorption through the skin
and consumption via food can also occur
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 portions of lungs are
damaged or destroyed
 Half of all lungs autopsied in US have some kind of lung deterioration
Plant pathology
• Chemical pollutants can directly damage plants, or can cause indirect damage
by disrupting normal growth and development patterns
 Certain environmental factors have synergistic effects in which the injury
caused by the combination is more than the sum of the individual
exposures
 Crop damage estimated at $10 billion per year in North America
Acid deposition
• pH and atmospheric acidity
 pH scale ranges from 0-14
 7 = Neutral; <7 = Acidic; >7 = Basic
 Unpolluted rain generally has ph of 5.6
 Carbonic acid from atmospheric CO2
 In industrialized areas, anthropogenic acids in the air often outweigh
natural sources of acid
Acid deposition
• Aquatic effects
 Thin, acidic soils and oligotrophic lakes of southern Norway and Sweden
have been severely affected by acid deposition
 Air pollutants are acidifying many North American lakes
Acid deposition
• Forest damage
 Air pollution and depositions of atmospheric acids are believed to be
important causes of forest destruction in many areas
Acid deposition
• 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
Visibility reduction
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
Air pollution control
• Reducing production
 Sulfur removal
 Switch from soft coal with a high sulfur content to low sulfur coal
 Change to another fuel (natural gas)
 Limestone Injection
 Can reduce sulfur emissions by 90% by mixing crushed limestone with
coal before it is fed into a boiler.
Air pollution control
• Nitrogen oxides
 Best method is to prevent creation
 Staged burners
 Selective catalysts
• Hydrocarbon control
 Use closed systems to prevent escape of fugitive emissions
Modern automobile emission-control system
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, environment, aesthetic and comfort
Clean Air Act
• Revision (1990) - Included provision for:
 Acid Rain
 Urban Smog
 Toxic Air Pollutants
 Ozone Protection
 Marketing Pollution Rights
 Volatile Organic Compounds
 Ambient Ozone
 Nox Emissions
• Revision (1997) - Stricter standards
Clear skies initiative of Bush
• Controversial elimination of “new source review”
 In 1977, power plants were “grandfathered” into Clean Air Act rules due to
expense
 Plant operators have continued to operate these polluting older power
plants
 New source review requires any updates to these aging power plants to
comply to Clear Air Act regulations
Current conditions and future prospects
• In the United States, air quality has improved dramatically in the last decade in
terms of major large-volume pollutants
 Cities where pollution is largely from traffic still have serious air quality
problems
 Houston passed Los Angeles as having the worst air quality in the country
Air pollution in developing countries
• Many metropolitan areas of developing countries are growing at explosive
rates
 Mexico City
 Pollution levels exceed WHO health standards 350 days per year
 China’s 400,000 factories have no air pollution controls
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
• South Coast Air Quality Management District in California has adopted rules to
clean the air in the Los Angeles Basin