air pollution
Article Contents: Types of Air Pollution Air Pollution Regulation Indoor Air Pollution
From: Encyclopedia of Physical Science.
Air pollution is the presence of unwanted particles and gases in the air that can adversely affect the
environment and the health of the organisms exposed to it. Two types of pollution sources exist: stationary
and mobile. Stationary sources include factories with smokestacks and industrial processes. As they burn
fossil fuels and complete the production process, they release multiple pollutants. The amount of pollution
in the air is a local, regional, and global problem. Air pollution is a local problem in that the geographical
area immediately surrounding the plant or polluting source is the first to experience the pollution. To
relieve the local effects of pollution, many plants began installing taller smokestacks, reducing the amount
of pollution released in the immediate vicinity of the plant. This practice creates a more regional problem
by spreading pollutants over a larger geographical area. Weather patterns and winds also affect the amount
of pollution that collects in an area.
Mobile pollution sources include cars, trucks, trains, boats, and airplanes. The regulation of mobile
pollution is difficult because the pollution sources are able to move from one location to another. Because
of this, mobile pollution sources are generally regulated at the production level. Automobile manufacturers
must follow emissions requirements for new automobiles, but the upkeep on these vehicles and
transportation fleets is then left primarily to the owners. Many states require emission testing for vehicle
licensure.
Types of Air Pollution
The age and overall health of an individual help determine how strongly he or she is affected by air
pollution. The most seriously impacted are the elderly, the young, and anyone who has a compromised
respiratory system, such as someone who is asthmatic, but air pollution can also negatively affect healthy
adult individuals. Exposure to airborne chemicals can cause symptoms such as respiratory irritation,
nausea, and rashes. The primary goal of regulating air pollution is to preserve human health, followed by
the desire to protect property and the environment from damage. The Environmental Protection Agency
(EPA) recognizes six primary pollutants (criteria pollutants) of concern to human health and property
protection including ozone (O3), sulfur dioxides (SO2), nitrogen oxides (NOx), carbon monoxide (CO),
particulate matter (PM), and lead (Pb).
Three covalently bonded oxygen atoms make up a molecule of ozone. While ozone is essential in the
stratosphere for protecting Earth's surface from harmful ultraviolet rays from the Sun, ozone at ground level
can be very damaging. Ozone forms by the reaction of oxides, such as nitrogen oxides, and hydrocarbons in
the presence of sunlight. Smog is composed of ground-level ozone, nitrogen oxides, particulate matter, and
aerosols. When the air near the ground is cooler than the air above it, the pollution particles and gases
become trapped at the surface of Earth, leading to the haze that is found over big cities.
Sulfur dioxide is a combustion product of sulfur-containing fuels such as coal and oil. When sulfur dioxides
are released into the atmosphere, they react with water to form sulfuric acid, causing acid rain. Normal
rainwater is slightly acidic with pH values around 5 to 6. High levels of sulfur dioxide in the air lower the
pH of precipitation; pH levels of rainwater have been recorded as low as 3.5. The environmental impact of
acid rain is seen in waterways as well as vegetation. Fish and other organisms living in lakes, rivers, and
streams are not able to thrive and in some cases cannot survive in water with a lowered pH. Vegetation also
suffers the effects of acid rain, leading to damaged plants, crops, and trees. The effects of acid rain caused
by sulfur dioxides do not stop there—nonliving matter is also affected. Acid rain causes deterioration of
buildings, statues, bridges, and roadways. Sulfur dioxide can also form sulfate particles that can cause
respiratory problems for everyone who breathes them but especially the young, the old, and those with
asthma or other preexisting respiratory or cardiac conditions.
Nitrogen oxides, NOx, refer to a class of covalent compounds formed between various numbers of nitrogen
and oxygen atoms. As sulfur dioxides do, nitrogen oxides form as a result of the combustion process.
Motor vehicles, followed by industrial processes that burn fuels, are the primary sources of nitrogen oxide
pollution. When released into the atmosphere, nitrogen oxides react with water to form nitric acid, which
contributes to the creation of acidic rain. Nitrogen oxides can also contribute to the formation of groundlevel ozone, which causes serious respiratory problems, as mentioned, and they can form nitrate particles
that can enter the body and damage lung and heart tissue. The environmental impact of nitrogen dioxides
includes an increased level of nitrogen in lakes and rivers, leading to eutrophication, or oxygen depletion,
and death of many organisms in the lake. Dinitrogen oxide N2O is considered a greenhouse gas that
contributes to global warming. Nitrogen oxides are the only criteria pollutant tracked by the EPA that has
not been reduced since the 1970s.
Carbon monoxide is a covalent compound of one carbon and one oxygen atom, formed from the
incomplete combustion of fossil fuels. More than half of the carbon monoxide in air is released from
automobile exhaust. This percentage is greater in highly congested traffic areas. Wood-burning fires,
including forest fires, also release carbon monoxide into the atmosphere. Carbon monoxide is a colorless,
odorless, tasteless gas that can be deadly. By competing with oxygen for binding sites on hemoglobin, the
oxygen carrier in red blood cells, carbon monoxide limits the amount of oxygen that a body receives.
Symptoms of carbon monoxide exposure include dizziness, nausea, and an inability to concentrate as well,
as heart and respiratory damage. The development of the catalytic converter in the 1970s was a major step
in reducing the level of carbon monoxide emissions from vehicles. These, along with other controls, have
helped reduce the amount of emissions that new cars produce but do not control how much is released as
the vehicle ages. The increased number of drivers on the road and the increased amount of time people
spend in their cars are coming close to offsetting the improvements in technology in carbon monoxide
emissions.
Particle pollution (or PM for particulate matter) is a class of inhalable particles smaller than 10 microns (a
micron equals one-millionth of a meter) in diameter, from various sources that are regulated by the EPA.
PM is a mixture of solids and liquids such as smoke, dirt, mold, and dust and is divided into fine particulate
matter that is less than 2.5 microns in diameter and particles with a diameter of 2.5 to 10 microns, termed
inhalable coarse particles. Because of the small size, particle pollution is most detrimental, since the
particles are able to pass deeply into lung tissue and create severe respiratory problems.
The element lead is a metal in group IVA of the periodic table of the elements with an atomic number of 82
and an atomic mass of 207.2. In the 1970s the primary source of lead pollution in the air was due to
automobiles' using leaded gasoline. The use of leaded gasoline was banned by the EPA in 1995, and the
development of automobiles that utilize unleaded gasoline has greatly reduced the amount of automobile
lead emissions. The majority of lead pollution presently originates in metal-processing plants.
Air Pollution Regulation
As pollution became more of a problem, Congress passed the first federal air pollution law, known as the
Air Pollution Control Act of 1955. The primary impact of this legislation was to call attention to air
pollution as a national problem and to grant research funds for exploring the problem more thoroughly. By
1963 sufficient research had been done that Congress passed the Clean Air Act of 1963, setting emissions
standards for stationary pollution sources. Several amendments to this act (in 1965, 1966, 1967, and 1969)
addressed issues such as monitoring the air quality in regions of the country and regulating emissions from
mobile pollution sources such as automobiles. The Clean Air Act of 1970 contained some of the most
stringent air pollution requirements and standards that had been written to date and significantly reduced
the allowable limits for stationary sources and mobile pollution sources. After this act, multiple
amendments pushed back deadlines for companies to meet these standards as well as raised the allowable
levels in order to make it easier for companies to be in compliance.
The Clean Air Act of 1990 revised and strengthened the older Clean Air Acts to account for newly
identified problems such as acid rain and ozone depletion. This more recent legislation focused on
investigations into controlling air pollution from motor vehicles and research into alternative energy
sources to replace fossil fuels. This act also addressed the atmospheric levels of chlorofluorocarbons
(CFCs) in order to reduce the effect on the stratospheric ozone layer according to the Montreal Protocol of
1985, which was amended in 1990, 1992, 1995, 1997, and 1999.
Indoor Air Pollution
Indoor pollution is potentially more damaging than outdoor air pollution as more and more Americans
spend their time indoors. Since the air flow inside the building is not fresh and is restricted, the pollutants
are "trapped" within the system. People are exposed to more concentrated doses of pollutants and for a
longer period, with dangerous effects on those that live and work in the structure. Pollutants such as
cigarette smoke, dust, mold, pet hair, toxic chemicals released from building supplies, carbon monoxide,
and radon are indoor air pollution concerns. Proper ventilation, appliance installation and maintenance,
proper ambient humidity, and restriction of smoking help minimize the harmful effects of indoor air
pollution.
Cigarette smoke is a predominant indoor pollutant. Secondhand cigarette smoke is now known to be as
dangerous to a nonsmoker as smoking is to the smoker. Working and living in areas where cigarette smoke
is present increase one's risk of lung cancer and respiratory problems, including asthma. As with most
respiratory pollutants, cigarette smoke has the greatest effect on the very young and the very old. In order
to improve indoor air quality, many states, such as New York, California, and Ohio, are adopting
antismoking legislation that bans cigarette smoking in public places.
Biological contaminants, such as pet dander, pet hair, mold, and other particulate matter, can pose a risk for
respiratory complications as well as allergies. The presence of toxic mold in a home can lead to memory
loss, allergies, and respiratory problems in healthy individuals. Young children and those with
compromised immune systems can have even more serious reactions, including death.
Chemicals released from indoor building supplies also pollute the air. Building materials that release
formaldehyde include particle boards, pressed wood used in furniture, and adhesives often used in carpets
and other furniture. Formaldehyde affects those with asthma and other breathing disorders and has also
been linked to cancer. The release of formaldehyde decreases over time, so the greatest risk occurs when
the furniture is new. Asbestos is another building product that has adverse affects on indoor air. Found
primarily in older homes and buildings, asbestos was used in insulation, siding, tiles, and other building
uses and poses its greatest risk when it is released as particulate matter into the air. Asbestos particles build
up in the lungs and can cause cancer. The EPA and Occupational Safety and Health Administration
(OSHA) began regulating asbestos in the 1970s.
As well as being an outdoor pollutant, carbon monoxide is a deadly indoor pollutant. Improper functioning
and venting of furnaces and other heaters that burn fossil fuels can produce carbon monoxide. Because it is
an odorless, tasteless gas, its detection requires an electronic carbon monoxide detector. Regular
maintenance of furnaces and heaters and installation of carbon monoxide detectors are important measures
for preventing carbon monoxide deaths.
Lead is also a harmful indoor pollutant. Prior to 1978 many paint products contained lead, and most homes
and furniture were painted with lead-based paint. When that paint chipped or released dust, the lead became
airborne and could be inhaled. Lead accumulates in bodily tissues and is especially harmful to infants and
small children. Low levels of lead in the body can damage many organs including the heart, kidneys, liver,
and brain.
Radon is an odorless, tasteless, radioactive noble gas with an atomic number of 86. As radium naturally
present in rocks decays and releases radon, the gas seeps into homes through basements and foundations.
Radon is the number one cause of lung cancer in nonsmokers. In 2007 the EPA estimated that radon
exposure causes 14,000–20,000 deaths per year, primarily from lung cancer. Radon exposure is second
only to smoking as a cause of lung cancer. Specific testing for radon is the only way to know whether this
gas contaminates a structure. Radon levels above four picocuries per liter (pCi/L) need to be mitigated.
Simple measures such as sealing cracks in the floor and walls and ventilating basements can help reduce
radon levels. Venting of the gases from below the foundation is known as subslab depressurization. This
method removes the radon gas before it can enter the home. These repairs should be performed by a
qualified radon contractor.