Chapter 24: Air Pollution

Chapter 24: Air Pollution
A Brief History of Air Pollution
• The atmosphere has long been a sink for
waste disposal.
• Long history of recognition of the existence
of atmospheric pollutants
– Natural photochemical smog recognized in
– Acid rain first described in 17th century
– Word smog introduced in 1905
• Mixture of smoke and fog
A Brief History of Air Pollution
• Two events sparked research on air
pollution and regulations to control air
– Donora fog in 1948
– London smog event in 1952
– Both cause by pollutants being trapped by
weather events. Both killed numerous people.
– Could happen again in cities like Beijing or
Mexico City
Stationary Source of Air
• Stationary sources are those that have a
relatively fixed location.
– Point sources emit pollutants from one or more
controllable sites.
– Fugitive sources generate air pollutants from
open areas exposed to wind processes.
– Area sources are well defined areas within
which are several sources of air pollutants.
Point source
Fugitive source
Mobile Source of Air Pollution
• Mobile source of air pollutants move from
place to place while emitting pollutants.
– Automobiles, trucks, buses, aircraft, ships, and
General Effects of Air Pollution
• Affects many aspects of our environment
Visual qualities
Water quality
Natural and artificial structures
Human health
General Effects of Air Pollution
• Significant factor in human death rate for
many large cities
– Athens, Greece- # of deaths higher on bad air
quality days
– Hungary- 1 in 17 deaths contributed to air
– US- 300,000 deaths/year, health cost $50 billion
– China- health cost $50 - $100 billion
General Effects of Air Pollution
• Affect human health in several ways
– Toxic poisoning, cancer, birth defects, eye
irritation, and irritation of respiratory system.
– Increased susceptibility to viral infections,
causing pneumonia and bronchitis.
– Increased susceptibility to heart disease.
– Aggravation of chronic diseases, such as
asthma and emphysema.
General Effects of Air Pollution
• Many air pollutants have synergistic effects
– Do greater damage to the lungs than a
combination of the two pollutants would be
expected to do based on their separate effects.
Air Pollutants
• 200 air pollutants recognized and assessed
by US EP and listed in Clean Water Act
– Six called critical pollutants
Primary and Secondary
• Major air pollutants occur either in gaseous
forms or as particulate matter.
• Classified as primary or secondary
– Primary pollutants- emitted directly into the air
– Secondary pollutants- produced through
reactions between primary pollutants and
normal atmospheric compounds.
Primary and Secondary
• In addition to human sources, our atmosphere
contains many pollutants of natural origin.
– Release of sulfur dioxide from volcanic eruptions.
– Release of hydrogen sulfide from geysers and hot
springs and from biological decay in bogs and marshes.
– Release of ozone in the lower atmosphere as a result of
unstable meteorological conditions.
– Emission of a variety of particles from wildfires and
– windstorms.
– Natural hydrocarbon seeps.
Criteria Pollutants
• There are six criteria pollutants
Sulfur dioxide
Nitrogen oxides
Carbon monoxide
Sulfur Dioxide
• SO2
– Colorless odorless gas
– Once emitted can be converted to sulfateSO4
– Removed from atmosphere by wet or dry
– Major human sources; coal power plants,
industrial processes
Sulfur Dioxide
• Adverse effects depend on dose and
concentration present
– Injury or death to animals and plants
– Corrosion of paint and metals
– Important precursor to acid rain
Nitrogen Oxides
• Occur in many forms in the atmosphere but
largely emitted in two forms:
– Nitric oxide- NO
– Nitrogen dioxide- NO2
• A yellow-brown to reddish-brown gas
• May be converted to NO32-
– Both subject to emissions regulation and
contribute to smog
– NO2 major contributor to acid rain
Nitrogen Oxides
• Nearly all NO2 emitted from human sources
– Automobiles and power plants that burn fossil
• Environmental effects
– Irritate eyes and mucous membranes
– Suppress plant growth
• However when convert to nitrate may promote plant
Carbon Monoxide
• CO is a colorless, odorless gas
– Even at low concentrations is extremely toxic
to humans
• Binds to hemoglobin in blood.
– 90% of CO in atmosphere comes from natural
– 10% comes from fires, cars, and incomplete
burning of organic compounds
Ozone and Other Photochemical
• Photochemical oxidants result from
atmospheric interactions of nitrogen dioxide
and sunlight.
– Most common is ozone- O3
– Colorless gas w/ slightly sweet odor
– Very active chemically, oxidizes or burns
• Beneficial in the upper atmosphere
Ozone and Other Photochemical
• Because ozone is a secondary pollutant it is
difficult to regulate.
– Health standards often exceeded in urban areas
• Effects include
– Kills leaf tissue at high concentration
– Damage eyes and respiratory system
– Even young, healthy people may have
breathing difficulty on polluted days
Particulate Matter
• PM10 is made up of particles less than
10μm in diameter
– Present everywhere but high concentrations
and/or specific types dangerous
– Much particulate matter easily visible as
smoke, soot, or dust
– Includes airborne asbestos and heavy metals
Particulate Matter
• Of particular concern are very fine
– PM 2.5- less than 2.5 μm in diameter
– Easily inhaled into the lungs, then absorbed into
the bloodstream
– Ultrafine particles- <0.18 μm released by
• Related to heart disease
Particulate Matter
• When measured often referred to as total
suspended particles (TSPs)
– Tend to be highest in large cities in developing
Particulate Matter
• Recent studies estimate that 2 to 9% of
human mortality in cites is associated w/
– Linked to both lung cancer and bronchitis
– Especially hazardous to elderly and those w/
• Dust can be deposited on plants
– Interferes w/ absorption of CO2 and O2 and
Particulate Matter
• Block sunlight and may cause climate
• Global dimming
– Gradual reduction in the solar energy that
reaches the surface of Earth
– Cools the atmosphere
– Lessens global warming
• Lead is constituent of auto batteries and
used to be added to gasoline.
– Lead in gas emitted into air w/ exhaust
– Spread widely around world in soils and water
along roadways
– Once in soil can enter the food chain
– Lead now removed from gas in US, CAN, EU
• 98% reduction in emissions since 1970s
Air Toxics
• Among pollutants that are known or
suspected to cause cancer or other serious
health problems.
– Associated w/ long-term and short-term
– Gases, metals, and organic chemicals that are
emitted in relatively small volumes
– Cause respiratory, neurological, reproductive,
or immune diseases
Air Toxics
• Standards have been set for more than 150
air toxics
– E.g. hydrogen sulfide, hydrogen fluoride,
chlorine gases, benzene, methanol, ammonia
– EPA estimates that the average risk for cancer
from exposure to air toxics is about 1 in 21,000
Hydrogen sulfide
• Highly toxic corrosive gas easily identified by its
rotten egg odor.
• Produced from
– Natural sources such as geysers, swamps, and bogs
– Human sources such as industrial plants that produce
petroleum or that smelt metals.
• Effects of hydrogen sulfide include
– Functional damage to plants
– Health problems ranging from toxicity to death for
humans and other animals.
Hydrogen Fluoride
• Extremely toxic gaseous pollutant
• Released by some industrial activities
– Such as production of aluminum, coal gasification, and
burning of coal in power plants.
• Even a small concentration (as low as 1 ppb) of
HF may cause problems for plants and animals.
– Potentially dangerous to grazing animals because
forage plants can become toxic when exposed to this
Methyl Isocyanate
• An ingredient of a common pesticide
– known in the United States as Sevin.
• Colorless gas
• Causes severe irritation (burns on contact) to eyes,
nose, throat, and lungs.
– Breathing the gas in concentrations of only a few ppm
causes violent coughing, swelling of the lungs,
bleeding, and death.
– Less exposure can cause a variety of problems,
including loss of sight.
Volatile Organic Compounds
• Variety of organic compounds used as
solvents in industrial processes
– Dry cleaning, degreasing, and graphic arts.
• Hydrocarbons
– Comprise one group of VOCs.
– Thousands of hydrocarbon compounds exist,
including natural gas, or methane (CH4); butane
(C4H10); and propane (C3H8).
Volatile Organic Compounds
• Some VOCs react w/ sunlight to produce
photochemical smog
• Globally 15% of hydrocarbons emissions
are anthropogenic
– In the US 50%
– Primary human source automobiles
• Additive in gasoline and an important
industrial solvent.
• Produced when gasoline and coal undergo
incomplete combustion.
– Also component of cigarette smoke
– Major environmental source on and off road
• A volatile hydrocarbon that is extremely
irritating to nose, eyes, and respiratory
• Produced from
– Manufacturing processes that involve
combustion of petroleum fuels
– Component of cigarette smoke
Variability of Air Pollution
• Problems vary in different regions of the
country and the world.
– LA pollution mainly from mobile sources
– Ohio and Great Lakes point sources
• Also varies w/ time of year
– Smog a problem in summer when there is lots
of sunshine
– Particulates a problem in dry months
Las Vegas: Particulates
• Particulates a problem in arid regions
– Where little vegetation is present and wind can
easily pick up and transport fine dust.
– Brown haze over Las Vegas partly due to
naturally occurring PM 10
– 60% of the dust comes from new construction
sites, dirt roads, and vacant land.
Haze From Afar
• Air quality concerns are not restricted to
urban areas.
– North slope of AK has an air pollution problem
that originates from sources in EE and Eurasia.
– Transported by the jet stream.
– Significant as we try to understand global air
Urban Air Pollution
• Whether air pollution develops depends on
topography and meteorological conditions
– Determine the rate at which pollutants are
transported away and converted to harmless
Influences of Meteorology and
• Meteorological conditions determine
whether air pollution is a nuisance or major
health problem.
• Primary adverse effect
– Damage to green plants and aggravation of
chronic disease
– Usually low-level over long period of time
– However major disaster have occurred
Influences of Meteorology and
• In the lower atmosphere, restricted
circulation associated w/ inversion layers
may lead to pollution events.
• Atmospheric inversion– Occurs when warmer air is found above cooler
in summer
and fall.
when cloud
w/ stagnant
Influences of Meteorology and
• Cities situated in a valley or topographic
bowl are more susceptible to smog
problems than cities in open plains.
• Surrounding mountains and inversions
prevent pollutants from being transported
by wind or weather systems.
– E.g. Los Angeles
Potential for Urban Air Pollution
• Determined by the following factors:
– 1. The rate of emission of pollutants per unit
– 2. The downwind distance that a mass of air
moves through an urban area.
– 3. The average speed of the wind.
– 4. The elevation to which potential pollutants
can be thoroughly mixed by naturally moving
air in the lower atmosphere.
Potential for Urban Air Pollution
• Concentration of pollutants in the air is
directly proportional to the first two factors.
– As either emission rate or down wind travel
distance increase, so will the concentration of
• City air pollution decreases w/ increases in
third and forth factors.
– The stronger the wind and the higher the
mixing layer, the lower the pollution.
• Term first used in 1905 as mixture of smoke
and fog that produced unhealthy air.
• Two major types
– Photochemical smog (LA type smog or brown
– Sulfurous smog (London type smog, gray air,
or industrial smog)
• Photochemical smog reaction involves
sunlight, nitric oxides and VOCs
– Directly related to automobile use
• Sulfurous smog is produced by the burning
of coal or oil at large power plants.
Future Trends for Urban Areas
• The optimistic view
– Air quality will continue to improve
– Because we know so much about the sources of air
pollution and have developed effective ways to reduce
• The pessimistic view
– In spite of this knowledge, population pressures and
economics will dictate what happens in many parts of
the world,
– The result will be poorer air quality in many locations.
Future Trends for Urban Areas;
The United States
• LA is a good area to look at for strategies for
pollution abatement.
• Air quality plan involving the entire urban region
includes the following features:
– Strategies to discourage automobile use and reduce the
number of cars.
– Stricter emission controls for automobiles.
– A requirement for a certain number of zero-pollutant
automobiles (electric cars) and hybrid cars with fuel
cell and gasoline engines.
Future Trends for Urban Areas;
The United States
– A requirement for more gasoline to be
reformulated to burn cleaner.
– Improvements in public transportation and
incentives for people to use it.
– Mandatory carpooling.
– Increased controls on industrial and household
activities known to contribute to air pollution.
Future Trends for Urban Areas;
The United States
• Have focused on LA because the air quality
is so poor for a significant portion of the
• However, many large and not so large US
cities have poor air quality
– 30 days per year of unhealthy air resulting from
ozone pollution.
Future Trends for Urban Areas;
Developing Countries
• Less developed countries w/ growing populations
are susceptible to air pollution
– Don’t have the financial base necessary to fight air
• E.g. Mexico City
25 million people
50,000 buses, millions of cars, LPG leaks
In a natural basin w/ mountains surrounding it
Perfect situation for severe air pollution problem
Future Trends for Urban Areas;
Developing Countries
• Attempts to reduce air pollution
– Shutting down oil refinery
– Ordering industrial plants to relocate
• Air pollution however will continue to be a
problem if unable to control vehicle use and
LPG leaks.
Pollution Control
• The most reasonable strategies for control
have been to reduce, collect, capture, or
retain the pollutants before they enter the
– Reduction of emissions through energy
efficiency and conservation measures is
Pollution Control: Particulates
• Particulates emitted from fugitive, point or
area stationary sources are much easier to
• Point and area sources can be controlled by
– Settling chambers or collectors which cause
particulates to settle out
• Fugitive sources
– Protecting open areas, controlling dust,
reducing effects of wind
Pollution Control: Automobiles
• Control of pollutants such as carbon
monoxide, nitrogen oxides, and
hydrocarbons is best achieved through
pollution control for automobiles.
– Nitrogen oxides controlled by recirculating
exhaust gas
– CO and hydrocarbons reduced by catalytic
Pollution Control: Automobiles
• Automobile emission regulations plan in US
has not been effective
– Pollutants may be low when car is new
– But many people do not maintain them properly
– Suggested that effluent fees replace emission
– Other strategies reduce the number or type of
Pollution Control: Sulfur Dioxide
• Can be reduced through abatement
measures performed before, during, or after
• Cleaner coal technology available but
makes fuel more expensive.
• Switch to low-sulfur coal
– But transportation is an issue
Pollution Control: Sulfur Dioxide
• Washing it to remove sulfur
– Iron sulfide settles out
– Ineffective for removing organic sulfur
• Coal gasification
– Converts coal to gas in order to remove sulfur
– Gas obtained is clean
Pollution Control: Sulfur Dioxide
• Emissions from power plants can be
reduced by removing the oxides from the
gases in the stack
Scrubbing (flue gas desulfurization)
Occurs after coal is burned
Gases treated w/ a slurry of lime or limestone
Reacts to form calcium sulfite
Can then be process into building materials
Clean Air Act Amendments of
• Comprehensive regulations enacted by the
U.S. Congress that address acid rain, toxic
emissions, ozone depletion, and automobile
• Buying and selling of sulfur dioxide
• One step back occurred in 2003 when the
president and EPA allowed companies to
upgrade w/o new pollution controls.
Clean Air Act Amendments of
• Also calls for control of
• Nitrogen dioxides
– Reduced by 10 million tons
• Toxins
– Especially those causing cancer
• Ozone depletion in the stratosphere
– End production of all CFCs
Ambient Air Quality Standards
• Important because they are tied to emission
standards that attempt to control air
• Tougher standards set for ozone and PM 2.5
– When challenged in court justices help that the
EPA’s responsibility is to consider benefits to
health not financial costs.
Air Quality Index
• AQI is used to describe air pollution on a
given day.
• AQI is determined from measurements of
the concentration of five major pollutants:
– Particulate matter, sulfur dioxide, carbon
monoxide, ozone, and nitrogen dioxide.
Air Quality Index
• An AQI value of greater than 100 is unhealthy.
• Air pollution alert is issued if the AQI exceeds
• Air pollution warning is issued if the AQI exceeds
300, hazardous to all people.
• If the AQI exceeds 400, an air pollution
emergency is declared, and people are requested to
remain indoors and minimize physical exertion.
Cost of Air Pollution Control
• Cost for incremental control in fossil fuelburning may be a few hundred dollars per
additional ton of particulates removed.
• For aluminum plant, may be several
thousand per ton.
• Also, a point is reached at which the cost of
incremental control is very high in relation
to additions benefits.
Cost of Air Pollution Control
• Economic analysis of air pollution includes many
variables, some of which are hard to quantify. We
do know the following:
– W/ increasing air pollution controls, the capital cost for
technology to control air pollution increases.
– As the controls for air pollution increase, the loss from
pollution damages decreases.
– The total cost of air pollution is the cost of pollution
control plus the environmental damages of the
Ozone Depletion
• Ozone (O3)
– Triatomic form of oxygen in which three atoms
of oxygen are bonded.
– Strong oxidant and chemically reacts with
many materials in the atmosphere.
– In the lower atmosphere, ozone is a pollutant.
– Highest concentration of ozone in the
Ultraviolet Radiation and Ozone
• Ozone layer in the stratosphere called the ozone
– Absorbs most of the potentially hazardous ultraviolet
radiation from the sun.
• Ultraviolet radiation consists of wavelengths
between 0.1 and 0.4 μm
– Ultraviolet A (UVA)
– Ultraviolet B (UVB)
– Ultraviolet C (UVC).
Ultraviolet Radiation and Ozone
• Ultraviolet C (UVC)
– Shortest wavelength and most energetic of the types of
ultraviolet radiation.
– Sufficient energy to break down diatomic oxygen (O2)
into two oxygen atoms.
– Each of these oxygen atoms may combine with an O2
molecule to create ozone.
• UVC strongly absorbed in the stratosphere, and
negligible amounts reach the Earth’s surface.
Ultraviolet Radiation and Ozone
• Ultraviolet A (UVA)
– Longest wavelength
– Least energy of the three types of ultraviolet
– UVA can cause some damage to living cells
– Not affected by stratospheric ozone, and is
transmitted to the Earth’s surface
Ultraviolet Radiation and Ozone
• Ultraviolet B (UVB)
– Energetic and strongly absorbed by
stratospheric ozone
– Ozone is the only known gas that absorbs UVB.
– Depletion of ozone in the stratosphere results in
an increase in the UVB that reaches the surface
of the Earth.
Ultraviolet Radiation and Ozone
• Approximately 99% of all ultraviolet solar
radiation (all UVC and most UVB) is
absorbed by the ozone layer.
– Natural service function
– Protects us from the potentially harmful effects
of ultraviolet radiation.
Measurement of Stratospheric
• First measured in 1920s using Dobson ultraviolet
– Dobson unit (DU)- 1DU = 1 ppb O3
– Now have measurements from all over the world for 30
• Ground based measurements first identified ozone
depletion over the Antarctic.
– Concentrations have been decreasing since the mid1970s
– “Ozone hole”
Ozone Depletion and CFCs
• Hypothesis that ozone in the stratosphere is
being depleted by CFCs
– First suggested in 1974 by Molina and
– Based on physical and chemical properties of
CFCs and knowledge about atmospheric
– Vigorously debated by scientists, companies
producing CFCs, and other interested parties.
Ozone Depletion and CFCs
• The major features of the hypothesis:
– CFCs emitted in the lower atmosphere are extremely
stable. Unreactive in the and therefore have a very long
residence time (about 100 years).
– CFCs eventually wander upward and enter the
– Once above the stratospheric ozone, they may be
destroyed by UV radiation, releasing chlorine, a highly
reactive atom.
Ozone Depletion and CFCs
– The chlorine released then depletes the ozone.
– Depletion increases the amount of UVB
radiation that reaches Earth’s surface.
– UVB is a cause of human skin cancers and is
also thought to be harmful to the human
immune system.
Emissions and Uses of Ozone
Depleting Chemicals
• CFCs have been used
– As aerosol propellants in spray cans
– Working gas in refrigeration and AC
– Production of Styrofoam
• No longer used in spray cans but use has
increased in refrigerants.
Simplified Stratospheric Chlorine
• CFCs are
– transparent to sunlight,
– essentially insoluble
– Non-reactive in the oxygen-rich lower atmosphere
• When CFCs reach the stratosphere, reactions do
• UVC splits up the CFC releasing chlorine, the
following two reactions can take place:
Cl + O3 → ClO + O2
ClO + O → Cl + O2
Simplified Stratospheric Chlorine
• This series of reactions is what is known as
a catalytic chain reaction.
– Chlorine is not removed
– Reappears in the second reaction
– Repeated over and over
• Process considerably more complex
• Chain can be interrupted and Cl stored in
other reactions
The Antarctic Ozone Hole
• Since 1958 ozone depletion has been
observed in the Antarctic every Oct.
– Thickness decreasing and geographic area
Polar Stratospheric Clouds
• Form during the polar winter (polar night)
– Antarctic air mass isolated from the rest of the
– Air circulates about the pole in Antarctic polar
– Forms as the isolated air mass cools, condenses,
and descends.
Polar Stratospheric Clouds
• Type I polar stratospheric clouds
– When air mass reach a temp between 195 K
and 190 K, small sulfuric acid particles are
frozen and serve as seed particles for nitric acid
• Type II polar stratospheric clouds
– If temperatures drop below 190 K water vapor
condenses around Type I cloud particles
Polar Stratospheric Clouds
• During the formation nearly all the nitrogen
oxides held in clouds
– Facilitates ozone depleting reactions
– When spring comes and sun returns it breaks
apart Cl2
– Chlorine can not be sequestered to form
chlorine nitrate, one of its carbon sinks.
An Arctic Ozone Hole?
• Polar vortex also forms over the North Pole
– Weaker and does not last as long as Antarctic
– Ozone depletion does occur at the NP
– Major concern is ozone-deficient air moving
southward over population centers.
Tropical and Midlatitude Ozone
• Evidence suggests an increase in ozone
depletion at midlatitudes over areas
including the US and Europe.
• We know the most about ozone depletion in
polar regions (particularly Antarctica), but
depletion of ozone is a global concern.
The Future of Ozone Depletion
• If the manufacture, use, and emission of all
ozone-depleting chemicals were to stop
today, the problem would not go away,
– millions of metric tons of those chemicals are
now in the lower atmosphere, working their
way up to the stratosphere.
• Several CFCs have atmospheric lifetimes of
75 to 140 years.
Environmental Effects
• Several serious potential environmental
– Damage to food chain on land and in oceans
(loss of primary production )
– Damage to human health (skin cancers,
cataracts, and suppression of immune system)
• UV Index measure of UV radiation on a given day
Environmental Effects
• Reduce the risk of skin cancer and other skin
damage from UV exposure by:
– Limit exposure to the sun between the hours of 10
A.M.and 4 P.M.
– When possible, remain in the shade.
– Use a sunscreen with an SPF of at least 30.
– Wear a wide-brimmed hat and, where possible, tightly
woven full-length clothing.
– Wear UV-protective sunglasses.
– Avoid tanning salons and sunlamps.
– Consult the UV Index before going out
Management Issues
• The Montreal Protocol
– Outlined a plan for the eventual reduction of
global emissions of CFCs to 50% of 1986
– Elimination of the production of CFCs by 1999
– Assessment of the protocol suggest that CFCs
will return to pre-1980 levels by 2050
Management Issues
• Substitutes for CFCs
– hydrofluorocarbons (HFCs) and
• Do not contain chlorine. However, fluorine atoms
participate in reactions similar to those of chlorine
but approximately 1,000 times less efficient in those
– hydrochlorofluorocarbons (HCFCs).
• Contain an atom of hydrogen in place of a chlorine
atom. Can be broken down in the lower atmosphere.
However, cause ozone depletion if they do reach the
stratosphere before being broken down.
Management Issues
• Short-term Adaptation to Ozone Depletion
– Given the nature of problem and the atmospheric
lifetimes of the chemicals that produce the depletion
– people will be learning to live with higher levels of
exposure to ultraviolet radiation.
• In the long term, achievement of sustainability w/
respect to stratospheric ozone will require
management of human-produced ozone-depleting

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