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Sustainable Air Quality- EPAAQ Summary 2001
As described in the EPA report on EPAAQ trends the six major pollutants are:
 Nitrogen Dioxide (NO2)
 Ozone (O3)
 Sulfur Dioxide (SO2)
 Particulate Matter (PM)
 Carbon Monoxide (CO)
 Lead (Pb).
All of these pollutants are regulated under the federal Clean Air Act which gives
responsibilities to the EPA to attempt to regulate and control these harmful pollutants.
Most of these pollutants are directly emitted; however, Ozone is a secondary pollutant
that is a combination of volatile organics compounds (VOC) and Nitrogen Dioxide that
react in the presence of sunlight. Particulate matter can also be produced indirectly as a
secondary pollutant but is also produced directly. Each pollutant is a little different and is
discussed in the following paragraphs.
Nitrogen Dioxide (NO2)
Nitrogen Dioxide (NO2) is a reddish brown gas that is highly reactive. It is
formed in ambient air through the oxidation of nitric oxide (NO). The general term for
nitrogen oxides is (NOx) and refers to the sum of a number of nitrogen oxides. These
pollutants play a major role in ozone formation, particulate matter formation, haze and
acid rain.
Major Sources
The major sources of NOx emissions are high-temperature combustion processes.
Typically these occur in automobiles and power plants but also home heaters and gas
stoves. These latter two sources can produce substantial amounts of pollution indoors.
Major Effects
The major effects to humans from this type of pollution are broken down into two
categories: short-term exposure and long-term exposure. Short-term exposure, usually
thought of as less than 3 hours, at even low level of nitrogen dioxide can lead to changes
in airway responsiveness and lunch function in those individuals with preexisting
respiratory illness. This same exposure can cause respiratory illness in otherwise healthy
children.
Long-term exposure to this type of pollution can lead to increased susceptibility to
respiratory infection and may cause irreversible alterations in lung structure. NOx
particles react in the ambient air to form ground-level ozone and fine particle pollution.
Both of these situations are tied to adverse health effects.
Besides direct effects to humans NOx pollutants contribute to other environmental
effects as well. Either directly or indirectly by combining with other pollutants, NOx is a
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precursor for acid rain and ozone. The excess nitrogen inputted into terrestrial and
wetland systems can have an extended effect on existing competitive relationships among
plant species that lead to changes in composition and diversity within the plant
community. In addition, the direct input of nitrogen to aquatic systems can lead to
eutrophication, a condition which can lead to excessive algae growth and a severe
depletion of dissolved oxygen.
Nitrogen along or through acid rain acts to acidify the solids and waters it
touches. The increase in acid concentration causes the plants to loose essential nutrients.
The increased acidity also increases the levels of soluble aluminum which is toxic to
plants. The low pH created and increased levels of aluminum are toxic to fish and other
aquatic organisms. Besides these harmful effects, NOx also contributes to visibility
impairment.
Spatial Distribution
The main areas of concentration are around cities. This is because cities contain
the major sources of this type of pollution. Big cities on either coast and in the south
contain this type of pollutant. Although all major cities experience this type of pollution.
Time Trend
In terms of trends the measured pollutant nitrogen dioxide as decreased 24 percent
over the last 20 years. All areas of the country that once violated the NAAQS for this
pollutant now meet that standard. No area of the country currently suffers nitrogen
dioxide levels above what the NAAQS calls for. Even though the air quality has
improved the total emissions of NOx has actually increased by 9 percent. This is still a
concern because of the effects mentioned earlier.
Ozone (O3)
Ozone is not emitted directly to the air but is a secondary pollutant. VOC’s and
NOx combine in the presence of heat and sunlight to form ozone. This is especially
prevalent in the hot summer months.
Major Sources
VOC’s are emitted from a lot of different sources. The list includes motor
vehicles, chemical plans, refineries, factories, consumer and commercial products and
other industrial sources. NOx as previously described is emitted primarily from sources
of combustion. Ozone with the help of wind can be spread hundreds of miles.
Major Effects
Ozone exposure has been tied to health effects including decreased lung function
and increased respiratory symptoms such as chest pain and a cough. Exposure to ozone
makes people more susceptible to respiratory infection. It can result in lung
inflammation and has the ability to aggravate preexisting respiratory diseases such as
asthma. When the ozone levels rise there has been noticed an increase in hospital
admissions for respiratory problems. These effects generally occur more often to people
who are active outdoors during the high ozone times, like summer. Long term exposure
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leaves the possibility of irreversible changes in lung structure and could lead to premature
aging of the lungs. Ozone also affects agriculture and plant life, leading to lower yields.
Spatial Distribution
Ozone distribution is largest on the east coast and in the south. The southern west
coast is similar with the least ozone being found in the Midwest-west regions. It is also
more abundant around big cities as these are the places that produce the pollutants that
form ozone.
Time Trend
Over the last 20 years the national ambient ozone levels have decreased 11
percent. This is do largely to a 16 percent reduction in VOC’s emissions but
counteracted by an increase of 9 percent of NOx emissions. All areas of the country have
improved although some areas more quickly than others.
Sulfur Dioxide (SO2)
Sulfur Dioxide is a gas that is formed when fuel containing sulfur is burned.
Major Sources
The major sources of sulfur dioxide are coal and oil. These fuels are burned
during metal smelting and other industrial processes. Fuel combustion largely from coalfired plans accounts for much of the SO2 emissions.
Major Effects
Sulfur dioxide can cause breathing impairment for asthmatic individuals who are
active outdoors. Symptoms of breathing difficulties include wheezing, chest tightness
and shortness of breath. High levels of SO2 also are linked to aggravation of existing
cardiovascular disease and respiratory illness.
Sulfur dioxide is also a major precursor to acid rain. Discussed earlier with NOx
emissions the acid rain is harmful to many ecosystems. These emissions also contribute
to poor visibility.
Spatial Distribution
Sulfur dioxide is largely concentrated around the big cities that employ the power
plants. The coal and oil fired combustion sources found in the east coast have the highest
distribution. Any of the large populated areas contain sulfur dioxide pollutants due to the
demand for energy.
Time Trend
Over the same time period SO2 emissions have decreased by 53 percent. These
are thought to be due in large part to the EPA’s Acid Rain Program started in 1995.
Particulate Matter (PM)
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Particulate matter is a term that encompasses a mixture of solid particles and
liquid droplets found in the air. They are divided into two groups. Those smaller than
2.5 micrometers and those between 10 and 2.5 micrometers.
Major Sources
PM can be directly emitted to the air as a primary particle or it can from in the air
as a secondary particle. Examples of primary emitted particles are dust and elemental
carbon. Secondary particles are formed from other pollutants like so2 and are usually
emitted from power plants and other commercial activities.
Major Effects
Any particle that is small enough to get into the lung can cause problems and this
is what any of these PM particles can do. Various health problems can arise that are
similar to the other pollutants. They aggravate respiratory conditions like asthma and
bronchitis. They have also been associated with heartbeat irregularities. As well as
affecting health PM also contributes to poor visibility.
Spatial Distribution
The largest concentration of PM pollution occurs in southern California followed
by the east coast as a general region. The mid-west to west does not have nearly the
same levels of concentrations that the areas around the biggest cities do.
Time Trend
Over the last 10 years average PM10 concentrations are down 14 percent while
direct emissions are down 13 percent. During this same time PM2.5 has also decreased
by 10 percent.
Carbon Monoxide (CO)
Carbon monoxide is a colorless, odorless gas that is formed from incomplete
combustion.
Major Sources
The most abundant source of the pollutant is motor vehicles. They account for 60
percent nation wide of CO emissions. Non-road vehicles account for the rest. High
concentrations generally occur around traffic zones. But, other sources include industrial
processes, non-transportation fuel combustion and natural sources like wild fires.
Major Effects
Carbon monoxide enters the bloodstream thought the lungs and directly reduces
the oxygen the body can deliver to the orgasm and tissue. This is most serious for people
who suffer from cardiovascular disease and higher levels can even be poisonous for a
healthy individual.
Spatial Distribution
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Carbon monoxide as described earlier is contained around large traffic zones and
areas that have a lot of combustion reactions taking place. Concentrations are higher
around cities.
Time Trend
In the past 20 years CO levels have dropped 62 percent and are at the lowest
levels in 20 years. The major contributor to CO, cars, has decreased emission slightly
during this period. The air quality improvement came despite a 35 percent increase in
vehicle miles driven. CO emissions are up 6 percent but this is due to an extremely
serious wildfire season in 2000.
Lead (Pb)
Lead is natural element that is toxic to humans
Major Sources
Major sources used to include automobiles but due to the efforts to reduce lead in
gasoline these types of emissions are greatly reduced. Today the primary culprits are
industrial processes, primarily metals processing. The highest concentrations are found
near smelters and battery manufacturers.
Major Effects
Lead, once in the body, accumulates in the blood, bones and soft tissues and can
adversely affect the kidneys, liver and nervous system. Even in small doses lead
exposure is linked to nervous system damage, lowered IQ and learning difficulties.
Spatial Distribution
Lead concentrations are very low almost everywhere but have there peaks near
where leaded cars once drove. Off of highways was once a problem spot. Now lead is
mostly concentrated around the industrial areas that emit the pollutant.
Time Trend
Due largely to the phase out of leaded gasoline lead concentrations are down 94
percent over the last 20 years while emissions are down 93 percent.