ENVR 1401 – BACKGROUND
Lab 12 – Air Quality
Objectives
The objectives of this lab activity are to:
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Define air pollution
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Describe major sources of indoor and outdoor air pollution
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Estimate the average amounts of annual air pollutants emitted by cars
Overview
Air pollution is nothing new. In the 1300s, England began to use coal instead of wood for heat, causing
major air pollution problems. To clean up London's air, King Edward I, outlawed coal burning
exclaiming, "…whosoever shall be found guilty of burning coal shall suffer the loss of his head."
A number of air pollution disasters have occurred around the world during the 20th century. The United
States experienced its first major air pollution catastrophe in Donora, Pennsylvania in 1948. Airborne
effluents including sulfur, carbon monoxide and heavy metal dusts from a number of industrial facilities,
including a sulfuric acid plant, a steel mill, and a zinc production plant, became trapped in a valley by a
temperature inversion and produced an un-breathable mixture of fog and pollution. Seven-thousand
people suffered illnesses ranging from sore throats to nausea. There were 20 deaths in three days. In
1984, an explosion occurred at a pesticide plant jointly owned by Union Carbide and Indian authorities.
The resulting cloud of toxic gases (including hydrogen cyanide and carbon monoxide), drifted over
Bhopal, India, and impacted half a million people. An estimated 20,000 people died and more than
120,000 individuals were permanently injured.
The major components of dry air at the surface of the Earth are as follows:
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Nitrogen (N2)
78.0%
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Oxygen (O2)
21.0%
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Carbon dioxide (CO2)
0.03%
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Other Trace Elements such as Argon & Helium <1.0%
In addition, air may also contain water vapor (ranging up to 4 %) and biologicals (e.g., bacteria, molds,
mildew, viruses, animal dander, dust, and pollen). Any substances present in the atmosphere in amounts
sufficient to harm humans, organisms, or materials are considered air pollution. These pollutants can be
gases or particulate matter (liquid or solid particles), and can be man-made or from natural sources. The
majority of man-made air pollutants originate from industry and the combustion of fossil fuels for energy,
whereas, natural air pollutants may result from a volcanic eruption, strong winds associated with storms,
or wildfires.
Revised: September 22, 2010
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As shown in the following figure, air pollutant sources can be either stationary or mobile. Stationary
sources are non-moving sources, fixed-site producers of pollution such as power plants, chemical plants,
oil refineries, manufacturing facilities, and other industrial facilities. Vehicles, engines, and equipment
that generate air pollution and that move, or can be moved, from place to place are called mobile sources.
Stationary Source
Mobile Source
Source: http://www.epa.gov/apti/course422/ap4.html
As shown in the following figure, air pollutants can also be classified as either primary pollutants or
secondary pollutants. A primary pollutant is one that is emitted directly into the atmosphere and retains
the same chemical form. An example of a primary pollutant is the carbon monoxide (CO) that is emitted
in the exhaust of an automobile. Secondary pollutants are formed by atmospheric reactions when a
primary air pollutant reacts with substances normally found in the atmosphere or with other air pollutants.
An example of a secondary pollutant is ozone created from organic vapors given off at a gasoline station.
The organic vapors react with sunlight in the atmosphere to produce the ozone, the primary component of
smog.
Primary and Secondary Air Pollutants
Source: Raven and Berg’s Environment, 6th ED, Wiley Publishing
Revised: September 22, 2010
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Formation of Smog
The primary factors affecting transport and
dispersion of pollutants are wind and stability.
Wind is the natural horizontal motion of the
atmosphere. It occurs when warm air rises,
and cool air comes in to take its place. Wind is
caused by differences in pressure in the
atmosphere. The pressure is the weight of the
atmosphere at a given point. The height and
temperature of a column of air determines the
atmospheric weight. Because cool air weighs
more than warm air, a high pressure mass of
air is made up of cool and heavy air.
Conversely, a low pressure mass of air is
made up of warmer and lighter air.
Differences in pressure cause air to move from
high pressure areas to low pressure areas,
resulting in wind. Wind speed can greatly
affect the pollutant concentration in a local
area. The higher the wind speed, the lower the
pollutant concentration. Wind dilutes
pollutants and rapidly disperses them
throughout the immediate area.
Revised: September 22, 2010
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Los Angeles: Sunny skies, smog layer
Los
Angeles
Revised: September 22, 2010
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Indoor Air Quality
Americans spend about 90% of their time in indoor environments, including homes, schools, offices, and
businesses. Studies conducted by the U.S. EPA and others indicate that the concentrations of many
pollutants indoors exceed those outdoors. Infants and young children, the elderly, and the chronically ill,
especially those suffering from respiratory or cardiovascular disease are often those most susceptible to
the effects of indoor air pollution and may be exposed to indoor air pollutants for the longest periods of
time.
Our growing demand for energy efficiency in homes and buildings has resulted in construction methods
that have made structures increasingly airtight. The reduction of air flow between the interiors of
buildings and the outside environment can result in the accumulation of pollutants from a variety of
indoor sources. Inadequate ventilation can increase indoor pollutant levels by not bringing in enough
outdoor air to dilute emissions from indoor sources and by not carrying indoor air pollutants out of the
home. High temperature and humidity levels can also increase concentrations of some pollutants.
Outdoor air enters and leaves a house or building by infiltration, natural ventilation, and mechanical
ventilation. Infiltration occurs when outside air flows into the house or building through openings, joints,
and cracks in walls, floors, and ceilings, and around windows and doors. With natural ventilation, air
moves through opened windows, doors and passive vents. In addition to infiltration and natural
ventilation, there are a number of mechanical ventilation devices, such as outdoor-vented fans that
intermittently remove air from a single room (such as bathrooms and kitchen), to air handling systems
that use fans and duct work to continuously remove indoor air and distribute filtered and conditioned
outdoor air to strategic points throughout the house or building. The rate at which outdoor air replaces
indoor air is described as the air exchange rate. When there is little infiltration, natural ventilation, or
mechanical ventilation, the air exchange rate is low and pollutant levels can increase, resulting in what is
called sick building syndrome. It is not the building that is “sick” but persons who spend significant
time indoors may develop illness as a result of exposure to poor indoor air quality.
The differences in pressure cause air to move, therefore, there must be a change in pressure for a potential
contaminant to move from a source to a person. Where there are differences of pressure between two
places, a pressure gradient exists, so air moves from higher-pressure to lower-pressure. In most modern
homes and buildings air is moved through a heating, air conditioning and ventilation (HVAC) system.
Fans draw air in through grilles called returns, lowering the atmospheric pressure (creating negative
pressure) and force air through ducts and into the conditioned space through supply registers. This
negative pressure collapses the duct whereas a positive pressure opens the duct so that the pressures can
be used to control temperature, airflow, and contaminants.
As shown in the following figure, potential indoor air pollutants include biological pollutants, carbon
monoxide, formaldehydes, lead, nitrogen dioxide, ammonia, chloroform, styrene, methylene chloride,
pesticides, radon, cigarette smoke (environmental tobacco smoke) and asbestos. Sources of these
potential pollutants include stoves, heaters, fireplaces, and chimneys, household cleaning products,
personal care products, and products associated with hobbies. Paints, laminated wood products, vinyl
flooring, carpet padding, adhesives, upholstered furniture, and draperies give off organic chemical fumes.
Combustion sources such as stoves, fireplaces, and water heaters create higher levels of nitrogen dioxide
indoors. Other potential pollutant sources include copying machines, electrical and telephone cables,
mold and microbe-harboring air conditioning systems and ducts, cleaning fluids, latex caulk, vinyl
molding, linoleum tile, and building materials and furniture that emit air pollutants such as formaldehyde.
Revised: September 22, 2010
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Sources of indoor air pollution in homes.
Source: http://www.epa.gov/apti/course422/ap4.html
There are four elements that must be present for an indoor air quality problem to exist and those elements
are:
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a contaminant
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a pathway to a person
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a driving force to move the contaminant
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a person exposed to the contaminant
If any of these elements is absent then the problem is minimized.
Immediate health effects from indoor air pollutants may include irritation of the eyes, nose, and throat, as
well as headaches, dizziness, and fatigue. Long term health effects from indoor air pollution may include
respiratory diseases, heart disease, and cancer. Even though common pollutants found in indoor air are
responsible for many harmful effects, there is considerable uncertainty about what concentrations or
periods of exposure are necessary to produce specific health problems. In part, this is because individuals
vary in tolerance and may also react very differently to exposure to indoor air pollutants.
Outdoor Air Quality
Although outdoor air quality has improved greatly over the last 30 years, Americans continue to hear
about air pollution as a result of our National dependence on petroleum. Beginning in the mid 1980s,
consumers began to buy more minivans, pickup trucks, and sport utility vehicles (SUVs) that burned
more gasoline per mile. They continue to discharge millions of tons of hazardous gases and particles
every year. But even where it is not visible, the effects on our health are evident. Air pollution can cause
a wide range of problems from minor respiratory irritations and headaches to the more serious
consequences of asthma, brain and nerve damage, cancers, birth defects, and even death. Unborn children,
Revised: September 22, 2010
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young children, and the elderly are especially at risk, along with those individuals with existing health
problems.
The major air pollutants associated with cars and the burning of gasoline are carbon monoxide (CO),
nitrogen oxides (NOx), ozone (O3), volatile organic compounds (VOCs), particulate matter (PM), and
lead (Pb). The burning of gasoline also produces carbon dioxide (CO2).
The Environmental Protection Agency (EPA) classifies outdoor air pollutants as hazardous air pollutants
(HAPs) and criteria pollutants. Hazardous air pollutants are those pollutants that are known or
suspected to cause cancer or other serious health effects. Criteria pollutants are those pollutants that are
common, widespread, and detrimental to human welfare. The six criteria pollutants are: carbon monoxide
(CO), nitrous oxides (NOx), particulate matter (PM), lead (Pb), sulfur dioxide (SO2) and Ozone (O3).
Carbon monoxide (CO) is a colorless, odorless, tasteless, poisonous gas produced by incomplete
combustion. Carbon monoxide can accumulate in areas where there is a lack of adequate ventilation such
as garages, tunnels, and even along roadsides when traffic is heavy. When inhaled, CO inhibits oxygen
intake in the blood and therefore prevents oxygen from reaching the brain, heart, and body tissue. The
effects of CO exposure can vary greatly from person to person depending on age, overall health, and the
concentration and length of exposure. Low concentrations can cause dizziness, headaches, fatigue and
nausea. Moderate concentrations can cause angina, impaired vision, and reduced brain function. High
concentrations can lead to unconsciousness and death.
Nitrogen oxides (NOx) include nitrogen monoxide (NO) and nitrogen dioxide (NO2) and other less
common nitrogen-oxygen compounds that form when fuel is burned at high temperatures. They also play
a major role in the formation of ozone, the primary component of smog. Nitrogen dioxide, (NO2) can
irritate the eyes and respiratory tract. Exposure can further impair lung function in individuals with
asthma, and it may cause other respiratory diseases such as chronic bronchitis. As a gas, it is highly
reactive with other compounds. As a solid, small particles can cause significant damage to air passages
and lung tissues. It also reduces visibility. Nitrogen oxides also react with water to form nitric acid,
contributing to acid rain increasing the natural acidity of precipitation.
Particulate Matter (PM) is made up of solid and liquid particles (e.g., nitrates, sulfates, organic
chemicals, metals, soil or dust) of various sizes ranging from those visible to the human eye to those that
are microscopic. Examples include soot, smoke, dust, aerosols, fumes, and mists. Larger particles can be
screened out by the nose and throat, but may irritate the nose and throat and trigger breathing difficulties.
But the smaller particles that are less than 10 micros (one-tenth of a millimeter) can find their way deep
into the lungs and become trapped. Particles that are less than 2.5 microns (PM2.5) are potentially most
damaging since they can be breathed into the lungs and may even be absorbed into the bloodstream.
There they can cause or exacerbate respiratory disease, damage or decrease lung function, cause irregular
heartbeats and non-fatal heart attacks, and can cause cancer. PM2.5 particles are the major cause of
reduced visibility (haze), and may be transported long distances by the wind. When particulates settle in
surface waters or on structures, the particles may dissolve in moisture and acidify surface waters or
damage material surfaces (e.g., statues, buildings, bridges).
Lead (Pb) is a toxic, heavy metal contributed by waste incinerators, power plants, lead-acid battery
manufacturing and lead smelting. Historically, lead was one of the most threatening air pollutants. EPA
regulations requiring the removal of lead from gasoline have significantly reduced lead levels in our air.
However, it still continues to cause some concern as the soils along some roadsides remain contaminated.
The unrelated issue of lead paint in older homes is a much more significant health concern. Lead
accumulates in the body so repeated exposure, as well as exposure to high concentrations, are both
harmful. It affects the nervous, reproductive, digestive, kidney, and blood forming systems. High
exposures can result in neurological disorders. Lead is persistent in the environments and accumulates in
soils and sediments where it can cause loss of biodiversity, changes in community composition, decrease
growth and reproductive rates in plants and animals.
Revised: September 22, 2010
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Sulfur oxides (SOx) include sulfur dioxide (SO2) and sulfur trioxide (SO3). Humans contribute about
one-third of all sulfur oxides in the atmosphere through mining and manufacturing processes. Coal
burning generates about half of the sulfur oxide emissions we release, while burning oil accounts for 25 to
30%. Smelting, manufacture of sulfuric acid, conversion of wood pulp to paper, and incineration of
refuse are other anthropogenic sources of atmospheric sulfur oxides. SO2 is a pollutant which causes
respiratory problems and is especially irritating to the lungs and may aggravate heart disease. Sulfur
dioxide particles significantly impair visibility. Sulfur oxides are a major component in the production of
acid rain which directly damages vegetation and can indirectly result in soils and surface waters becoming
more acidic.
Ozone (O3) is the most widespread air pollution problem. It is formed when NOx and VOCs react in the
presence of sunlight. The result is an intensely irritating gas that is the major component of smog.
Warmer temperatures increase the amount of ozone formed, hence it is more problematic with higher
temperatures during the summer months. Ground-level ozone can worsen respiratory diseases such as
bronchitis, emphysema and asthma. Breathing ozone can irritate the throat and reduce lung function,
repeated exposures may permanently scar lung tissues. Vegetation can also be impacted, with a
significant reduction in crop productivity.
Other potential pollutants that are not criteria pollutants but are of concern are carbon dioxide (CO2) and
volatile organic compounds (VOCs). CO2 is a natural component (< 0.04%) of air. We exhale it and
plants need it for photosynthesis. It is also a product of the complete combustion of gasoline. CO2 is also
a heat-trapping or “greenhouse” gas. CO2 has no direct impact on health, unless it is breathed in very
high concentrations (greater than 2 % concentrations) which may cause fatigue and a feeling of heaviness
when breathing.
Volatile Organic Compounds (VOCs) result from the incomplete burning of fuel such as gasoline,
wood, coal, and natural gas. Many commonly used solvents, paints and varnishes, glues and adhesives,
pesticides, building materials, aerosols sprays and other products release VOCs. At room temperatures,
vapors readily escape from chemicals used in a wide range of industrial processes. They are also released
by evaporation of gasoline itself, such as while refueling at gas stations. Vehicle emissions are an
important source of VOCs. Many VOCs are hazardous air pollutants; for example, benzene causes
cancer. VOCs react with nitrogen oxides in the presence of sunlight to form ozone, the major component
of smog. Direct exposure to VOCs may cause irritation of eyes and the respiratory tract, headaches, loss
of coordination, nausea, damage to the liver and kidneys, as well as allergic skin reactions.
Revised: September 22, 2010
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