United States July 1978
Environmental Protection OPA 11/8
Agency
vvEPA Measuring
Air Quality
The New
Pollutant
Standands
Index
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Unhealthy,
Examples of possible PSI report for television
Today's
Index
Good
T"~
Moderate
50
100
200
300
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The New Air Pollutant Standards Index
The American people, especially those who
suffer from illnesses aggravated by air
pollution, need accurate, timely, and easily
understandable information about daily
levels of air pollution. This information
would allow them to modify their activities
when air pollution levels are high, or to
take other temporary measurers to protect
themselves.
One way of conveying air pollution infor-
mation is to report the concentration of
each pollutant. However, different pollu-
tants affect health at different concentra-
tions; thus, anyone wanting to act on the
information must remember several dif-
ferent sets of numbers. An air pollution in-
dex can avoid this problem by relating
similar degrees of health effects to a
uniform numerical scale that is based on
actual pollutant concentrations
In recent years, a number of cities and
States have developed various indices to
respond to the public need for daily reports
on air pollution levels. Of all those indices
used to date, however, no two have been
the same. An air quality index of 25 in one
city, for example, might not represent the
same level of air pollution as an index value
of 25 in another city. And, depending on
how the index is determined, the air quality
might be called "excellent" in one, and
"unhealthy" in the other. Thus, instead of
clarifying the health implications of air
pollutants, the use of differing indices has
added to the public's confusion, especially
when two different systems were operated
side by side in neighboring cities or States.
To avoid this confusion and to provide
clear, consistent advice to the public, the
U.S. Environmental Protection Agency
(EPA), in cooperation with the Council on
Environmental Quality (CEQ) and other
agencies, developed the Pollutant Standards
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Index (PSD
PSI provides a simple, uniform way to
report daily air pollution concentiations, to
tell the public about the general health ef-
fects associated with these concentrations,
and to describe some general precautionary
steps that can be taken (Table 1) PSI is a
reporting tool that converts the pollutant
concentrations measured in a community's
air to a simple number on a scale of 0 to
500. Intervals on the PSI scale are related
to the potential health effects of the daily
measured concentrations of five ma|or
pollutants: carbon monoxide, photochemical
oxidants, nitrogen dioxide, sulfur dioxide,
and paniculate matter. The intervals and
the terms describing the air quality levels,
are1
From 0 to 50, "good"
Above 50, "moderate"
Above 100, "unhealthful"
200 to 299, "very unhealthful"
300 and above, "hazardous"
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i "•'•"'''"' lOn^fSlc
The index value of 100 was selected to
correspond to the short-term (24 hours or
less) National Ambient Air Quality Standard
(NAAQS) set by EPA to represent the con-
centration for each pollutant below which
adverse health effects have not been
observed Each value has built into it a
margin of safety that, based on our current
knowledge, protects the highly susceptible
members of the public.
For each air pollutant, the observed con-
centration is first divided by the NAAQS
value, creating a dimensionless number, or
"submdex " Then, PSI is reported as the
maximum submdex. The particular pollutant
responsible for this maximum submdex also
is reported On days when two or more
pollutants violate their respective NAAQS—
that is, have PSI values greater than 100
— then each pollutant also will be reported.
The highest PSI value, 500, corresponds
to the "significant harm level," established
by EPA as the concentration of each pollu-
tant that never should be reached As air
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quality approaches this level, the sick and
elderly may die prematurely, and even
healthy persons will experience symptoms
that will affect their normal activity. State
and local agencies are required to take
emergency action to prevent air pollution
from reaching the significant harm level,
such as restricting auto traffic and
manufacturing activities.
Once the value of 100 had been selected,
four equal intervals between 100 and 500
Index Value PSI Descriptor
very unhealthful
too
moderate
50
good
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were marked off at index values of 200,
300, and 400. The index intervals between
these points approximate the concentration
ranges in which adverse health effects in-
crease in severity, and the number and
types of people affected rise as well. The
actual values of these points are not known
with great precision, and, of course, a
given health effect does not start or stop
exactly one index number above a given
point.
General Health Effects
Cautionary Statements
Premature death of ill and elderly
Healthy people will experience
adverse symptoms that affect
their normal activity.
Premature onset of certain
diseases in addition to significant
aggravation of symptoms and
decreased exercise tolerance in
healthy persons.
All persons should remain in-
doors, keeping windows and
doors closed. All persons should
minimize physical exertion and
avoid traffic
Elderly and persons with existing
diseases should stay indoors and
avoid physical exertion. General
population should avoid outdoor
activity.
Significant aggravation of symp-
toms and decreased exercised
tolerance in persons with heart or
lung disease with widespread
symptoms in the healthy popula-
tion
Elderly and persons with existing
heart or lung disease should stay
indoors and reduce physical
activity
Mild aggravation of symptoms in
susceptible persons, with irrita-
tion symptoms in the health
population
Persons with existing heart or
respiratory ailments should
reduce physical exertion and out-
door activity.
Table 1, PSI values, descriptor words,
generalized health effects, and cautionary
statements
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Federal
Episode
Criteria
How PSI
Will Be
Reported
PSI is a standardized reporting system for
advising the public of any adverse health
effects due to air pollution, no matter what
the level may be. Its official use is not in-
tended as a substitute for the actions local
and State governments must take to limit
the adverse effects of air pollution during
air pollution episodes. For these emergency
situations, EPA has published Federally
suggested episodes criteria which specify
three stages of air pollution levels: Alert,
Warning, and Emergency Each stage calls
for different control actions, such as reduc-
ing traffic, limiting fuel use, restricting in-
cineration, and reducing manufacturing ac-
tivities. To determine which stage is to be
called, officials examine not only current
pollutant concentrations, but also prevailing
and predicted metrological conditions. PSI
values of 200, 300, and 400 for the most
part correspond to the Alert, Warning, and
Emergency levels in recommended episode
criteria. However, because many factors,
including meteorological conditions, are
taken into account before triggering
episode control actions, reported PSI
values and the calling of an episode do not
always exactly correspond.
PSI places maximum emphasis on acute
health effects occurring over very short
time periods — 24 hours or less — rather
than chronic effects occurring over months
or years. It therefore facilitates protection
of public health during such periods by pro-
viding information on which individuals can
act to reduce their exposure to air pollu-
tion. It stresses reporting on the basis of
the sampling stations with the highest
pollutant concentrations, and assumes that
areas of the community where pollutants
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are not measured also are experiencing
high concentrations Because the Federal
health-related air pollution standards in-
clude a safety factor, warning the public
when a standard (a PSI value of 100) is
reached at some location is reasonably con-
servative action.
Because of variations in air quality data —
collection points among the cities, PSI
should not be used to compare the relative
healthfulness of different cities. Such com-
parisons depend on other factors, such as
the total area of the community that is af-
fected by high concentrations, the duration
of these concentrations, and the number of
people actually exposed.
PSI is a health-based index and so does
not take into account the damage air pollu-
tants can do to animals, vegetation, and
materials (building materials and metals for
example). The PSI system is designed to
minimize confusion between health impact
and the other environmental effects
suspected to occur at these same concen-
trations. Local regulatory agencies reporting
the index, however, also can point out the
possible occurrence of agricultural and pro-
perty damage in their areas at appropriate
PSI values.
PSI allows for flexible reporting A typical
radio announcement might read: "The
pollution index today is 150, and the air is
considered unhealthful. The pollutant caus-
ing this condition is photochemical ox-
idants. Patients with respiratory ailments
and heart diseases should reduce physical
exertion and outdoor activity. The forecast
for tomorrow calls for no change in the in-
dex." A more detailed account could be
provided by recorded telephone reports or
newspapers.
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As presently designed, PSI reports on five
major air pollutants. However, it need not
be limited to these; it also could accommo-
date other substance on which minimum
acceptable standards are set to protect
public health. PSI does not take into ac-
count the possible adverse effects
associated with combinations of pollutants
(synergism), but may be modified in the
future to include such effects as more
research knowledge is obtained.
Carbon monoxide (CO) is a by-product of
the incomplete burning of fuels — notably
by automobiles in most large urban areas
— and is also released by some industrial
processes. It is inhaled and enters the
blood stream; there it binds chemically to
hemoglobin, the substance that carries ox-
ygen to the cells, thereby reducing the
amount of oxygen delivered to all tissues of
the body. The percentage of hemoglobin
inactivated by CO depends on the amount
of air breathed, the concentration of CO in
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air, and length of exposure. Cigarette
smoke contains CO. Therefore cigarette
smokers have a portion of their hemoglobin
inactivated by this source as well as by air
pollution.
CO weakens the contractions of the heart,
thus reducing the amount of blood pumped
to various parts of the-body and, therefore,
the oxygen available to the muscles and
various organs. In a healthy person, this ef-
fect significantly reduces the ability to per-
form physical exercises. But in a patient
with heart disease, who is unable to com-
pensate for the decrease in oxygen, the ef-
fect can threaten life. Changes have been
observed in the electrocardiograms of per-
sons with coronary artery disease after they
have been in heavy freeway traffic, where
they would receive a fairly high exposure to
the carbon monoxide coming out of
tailpipes of motor vehicles.
Individuals with anemia, emphysema, or
other lung disease, as well as those living
at high altitudes, are likely to be more
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susceptible to the effects of CO. Even at
relatively low concentrations, CO can affect
mental function, visual activity, and alert-
ness.
Photochemical ox/dants are not released
directly into the atmosphere but are pro-
duced by a complex series of chemical
reactions that occur when nitrogen dioxide
and reactive organic substances — such as
hydrocarbons in auto exhaust, gasoline
vapors, or vapors from other sources such
as cleaning solvents — are exposed to
sunlight. This type of pollution first gained
attention in the 1940's as Los Angeles
"smog." Since then, photochemical smog
has been observed frequently in many other
cities as well.
Ozone, the main constituent of photo-
chemical oxidants, and peroxyacyl nitrates
are associated with a number of health ef-
fects in humans. Peroxyacyl nitrates and
other chemicals such as aldehydes cause
the eye irritation that is characteristic of
photochemical pollution. The principal
health effect of ozone is on the respiratory
system, where it severely irritates the
mucous membrances of the nose and
throat Ozone impairs normal functioning of
the lungs and reduces the ability to perform
physical exercises; the effects are more
severe in individuals with chronic lung
disease. The length of exposure, frequency
of exposure, and ozone concentration are
significant in determining the effects. In-
dividuals with asthma or diseases of the
heart and circulatory system experience
symptoms at lower concentrations than
normal people do. It also appears that
ozone in combination with sulfur dioxide
has a greater effect on respiratory function
than either pollutant alone.
Nitrogen dioxide (N02) is one of a family of
10 oxides of nitrogen. Those nitrogen oxides
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important in air pollution usually enter the
air as the result of high-temperature com-
bustion processes, such as those occurring
in automobiles and power plants. N02 plays
an important role in the atmospheric reac-
tions which generate photochemical ox-
idants.
Based on occupational exposures of
miners, chemists, and other industrial
workers, continued or frequent exposure to
high levels of N0;> has been shown to pro-
duce pulmonary edema. In a community
where N02 concentrations were elevated,
children exposed to peak N02 ambient con-
centrations of about 225 micrograms per
cubic meter, appeared to suffer higher
bronchitis rates than normal. Such high
concentrations are not believed to occur
often or in many cities at present, and the
health effects of high air pollutant concen-
trations for short periods of time are uncer-
tain and still under study Symptoms may
be aggravated in individuals with chronic
bronchitis and emphysema Animal studies
suggest that NO2 exposure impairs
resistance to infections.
Sulfur dioxide (S02) is one of a number of
sulfur containing comp.ounds found in the
atmosphere. It enters the air primarily from
the burning of coal and oil, but also from
various other industrial processes. Studies
of serious air pollution episodes have found
an increase in death rates among people
with existing heart and lung disease when
high concentrations of S02 are present in
combination with high concentrations of
total suspended particulate matter Even at
concentrations of these pollutants in the
atmosphere lower than those found during
episodes, prevalence of acute and chronic
respiratory diseases increases, and chronic
respiratory disease may be aggravated.
Other sulfur compounds such as sulfuric
11 acid, sulfates, and sulfites, formed when
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SO2 reacts in the atmosphere may be more
irritating to the respiratory system than S02
However, at present not enough is known
about these pollutants to permit EPA to
take any specific regulatory steps, other
than controlling S02, which generally
lowers the concentrations of the other
sulfur compounds.
Total suspended paniculate (TSP) matter is
the general term for particles found in the
atmosphere. Most of the TSP is composed
of dust, soot, organic matter, and com-
pounds containing sulfur, nitrogen, and
metals. Some particles may be formed in
the air as result of various chemical and
physical processes, which causes the
chemical composition of TSP to differ
widely with time and geographical location.
While certain components in TSP are con-
sidered to be inactive in the human body,
other components, such as sulfates,
nitrates, and metals, are being studied to
12 determine their contribution, if any, to the
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adverse health effects observed from
elevated TSP levels. When airborne par-
ticles are inhaled, they may irritate the
respiratory system, or damage the
clearance mechanism of the lungs, thereby
contributing to acute respiratory illnesses in
much the same way as gaseous pollutants
do. Prolonged inhalation of certain com-
ponents of airborne particles may increase
the number of cases and the severity of
chronic respiratory diseases.
For More A copy of the Federal Task Force Report
Information on Air Quality Indicators can be obtained
from the Council on Environmental Quality,
722 Jackson Place, N.W., Washington,
D.C. 20006. The Guideline for Public
Reporting of Daily Air Quality—Pollutant
Standards Index /PS/). EPA-450/2-76-013,
can be obtained from the U.S. Environmen-
tal Protection Agency, Office of Air Quality
Planning and Standards, Research Triangle
Park, NC 27711.
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(£ 3 C/J
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