Criteria Pollutants
Criteria pollutants include six air pollutants for which the U.S. EPA
has established health-based limits and two other pollutants which
transform into criteria pollutants in the air. They include carbon
monoxide, nitrogen
oxides, lead, sulfur
dioxide, particulate
matter, ozone,
and ozone precursors, volatile
organic compounds and ammonia.
Carbon monoxide (CO) is
a colorless, odorless gas produced by incomplete burning of carbon
in fuels. More than
75 percent of the carbon monoxide emissions in the United States are from transportation
sources, particularly highway motor vehicles. Other major sources
are wood-burning stoves, incinerators, and fuel combustion at industrial
sources.
When carbon monoxide is inhaled, it enters the bloodstream
and reduces the delivery of oxygen to organs and tissues. Symptoms
of CO poisoning include headaches or dizziness, nausea, fatigue,
and mental or visual impairments.
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Nitrogen oxides (NOx) are formed when fuel
is burned at high temperatures. The two major emissions sources
are motor vehicles and stationary fuel combustion sources. Nitrogen
dioxide (NO2) comprises about 10% of the oxides of nitrogen that are
formed when nitrogen in the air combines with oxygen during high temperature
combustion. Most of the rest of the nitrogen oxides emitted by combustion
sources is nitric oxide (NO). However, during the day most of the nitric
oxide is photochemically transformed into nitrogen dioxide. Thus, essentially
all the nitrogen oxides emitted can be assumed to eventually become
nitrogen dioxide.
When inhaled, nitrogen dioxide can irritate lungs, cause bronchitis and pneumonia. Nitrogen
oxides are also important because they are precursors to both ozone and acid
rain and, as a result, may affect not only human health, but also both terrestrial
and aquatic ecosystems.
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Lead (Pb) is a heavy metal
found in dust and soils. Some sources of lead used to be lead-based
paints and leaded-fuels, but now smelters and battery manufacturers
comprise the major sources.
Lead can either be inhaled or ingested, causing adverse health effects ranging
from disorders of the nervous system to problems involving kidney function or
digestion.
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Sulfur Dioxide (SO2) is
a colorless, pungent gas, having the same odor as a struck match. Ambient
sulfur dioxide results largely from stationary sources such as coal
and oil combustion, steel mills, refineries, pulp and paper mills, and
nonferrous smelters.
Sulfur dioxide is a respirator irritant and, like nitrogen oxides, is a precursor
to acid rain. It can also interact with other compounds in the are to
form particulate matter.
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Particulate
Matter (PM10 and PM2.5) includes dust,
dirt, soot, smoke and liquid droplets. Particulate matter originates
from a variety of sources, such as:
- Windblown dust and fires;
- Combustion of fuels in motor vehicles, for power generation, at
industrial facilities, and in residential fireplaces and wood stoves.
Combustion sources emit particles of ash or incompletely burned materials;
- Materials handling, crushing and grinding operations, and travel
on unpaved roads; and
- Interaction of gases, such as ammonia, sulfur dioxide, nitrogen
oxides and volatile organic compounds, with other compounds in the
air.
Particulate matter is divided into "coarse" particles, known as
PM10 because they are particles under 10 microns in size,
and "fine" particles, known as PM2.5 because they
are particles under 2.5 microns in size. Sulfate and nitrate secondary
particles represent significant components of PM2.5.
The most frequent health problems associated with particulate matter
occur within the respiratory system, including but not limited to irritation
of the nasal passages and throat. Bronchitis and even lung damage can
also occur.
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Ozone, a colorless gas,
is the major component of smog. Ozone is not emitted directly
into the air but is formed through complex chemical reactions between
precursor emissions of volatile organic compounds (VOCs), nitrogen oxides,
and ammonia in the presence of sunlight. These reactions are accelerated
by sunlight and increased temperatures. Sources include factories,
landfills, automobiles, gas stations, auto-body shops and even lawn
equipment.
Ozone causes health problems because it damages lung tissue, reduces
lung function, and sensitizes the lungs to other irritants.
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Volatile organic compounds (VOCs) are
ozone precursors. They react with with nitrogen oxides in the
atmosphere to form ozone. VOCs are another by-product of fossil
fuel combustion and emitted from motor vehicle fuel distribution, chemical
manufacturing, and a wide variety of industrial, commercial, and consumer
solvent uses.
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Ammonia (NH3) Ammonia
is a naturally occurring, colorless, acrid-smelling gas. It is widely
used in a variety of manufacturing processes, but is mostly used as
a fertilizer. Much of the ammonia in air results from the decomposition
of organic matter and other biological activities. Ammonia is not a
criteria pollutant but is regulated as a precursor for PM2.5 which
is a criteria pollutant. Hence it is regulated similar to other criteria
air pollutants.
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Useful Links
- Six Common Air Pollutants - U.S. EPA (http://www.epa.gov/air/urbanair/6poll.html)
This site is the first stop to learn more about the criteria pollutants
and why they are regulated.
- National Ambient Air Quality Standards (NAAQS) - U.S. EPA (http://www.epa.gov/ttn/naaqs/)
This site contains detailed information on each criteria pollutant
and further information about the control programs in place to meet
these standards.
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