United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park, NC 27711
EPA-454/R-99-010
July 1999
Air
& EPA
GUIDELINE FOR REPORTING OF
DAILY AIR QUALITY - AIR QUALITY
INDEX (AQI)
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GUIDELINE FOR REPORTING OF DAILY
AIR QUALITY - AIR QUALITY INDEX (AQI)
U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
July 1999
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Disclaimer
This draft has been reviewed and approved for publication by the U.S. Environmental Protection
Agency's Office of Air Quality Planning and Standards. Mention of trade names or commercial
products are not intended to constitute endorsement or recommendation for use.
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Guideline for Reporting of Daily Air Quality
Air Quality Index (AQI)
This guidance is designed to aid local agencies in reporting the air quality using the AQI as
required in Part 58.50 of 40 CFR and according to Part 58 of 40 CFR, Appendix G.
Do I have to report the AQI?
Part 58.50 states that Metropolitan Statistical Areas (MSAs) with a population of more than
350,000 are required to report the AQI daily to the general public. Table A-l in the Appendix lists all
the MSAs in the country that have a population of more than 350,000 according to the 1990 census. A
complete list of MSAs may be found in the Statistical Abstract of the United States (1998).
How often do I report the AQI?
Appendix G states that MSAs must report the AQI on a daily basis. The appendix further
defines daily as at least 5 times each week. This definition allows for days when personnel are not
available to provide the AQI report or for equipment failures.
How do I provide the AQI report to the general public?
You must provide the report to the local media (newspapers, radio, television), and you must
make the report available at one or more places of public access, provide a recorded telephone message,
or publish the report on a publicly accessible web page on the Internet. Other programs, including real-
time data reporting and community action programs (e.g., ozone action day programs) that provide
timely air quality information to the public, may also be used to meet reporting requirements. When the
AQI value is above 100, it is critical that the reporting be as extensive as possible. At a minimum, it
should include notification to the media with the largest market coverages for your area.
What is in my AQI report?
Your AQI report must contain:
• The reporting area(s)
• The reporting period
• The critical pollutant
• The AQI
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The category descriptor and, if reported in a color format, the associated color.1 Use only the
following names and colors for the six AQI categories:
Table 1. AQI Categories, Descriptors, and Colors
for this AQI... Use this descriptor... and this
color2
0 to 50 "Good" Green
51 to 100 "Moderate" Yellow
101 to 150 "Unhealthy for Sensitive Groups" Orange
151 to 200 "Unhealthy" Red
201to300 "Very Unhealthy" Purple
301 and "Hazardous" Maroon
above
• The groups most sensitive to the specific pollutant for any reported index greater than 100. Use
the following sensitive group statements for each pollutant:
Table 2. Pollutant Specific Sensitive Groups
When this pollutant has an index above 100... Report these Sensitive Groups...
Ozone Children and people with asthma are the groups
most at risk.
PM2 5 People with respiratory or heart disease, the
elderly and children are the groups most at risk.
PM10 People with respiratory disease are the group
most at risk.
CO People with heart disease are the group most at
risk.
SO2 People with asthma are the group most at risk.
1 A recorded phone message or a radio broadcast cannot show colors but can name a color in the report
(e.g., this is a category "red" day).
2 Suggested color formulations are given in Table 4.
2
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NO,
An AQI report may also contain:
Children and people with respiratory disease are
the groups most at risk.
• The name and index value for other pollutants, particularly those with an index value greater
than 100.
• The index for sub-areas of the reporting area.
• Actual pollutant concentrations.
• Causes for unusual AQI values.
• Health effects and cautionary language.
• Statements that "blend" the health effects statements or the cautionary statements for more than
one pollutant, if there is more than one pollutant with an index value greater than 100.
What does an AQI report look like?
The following examples of AQI reports present various methods of reporting the AQI which you
can use.
Example 1. A short form for a newspaper.
The Air Quality in Durham yesterday
The AIR QUALITY in Durham
yesterday was Moderate due to ozone.
The air quality index was 57.
MODERATE
UNHEAL THY for SENSITIVE GROUPS
HAZARDOUS
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Example 2. A short form for a newspaper in black and white.
Air Quality for Washington, B.C.
T Today's forecast A Yesterday
Air Quality Index (AQI)
Green
Yellow
0 50
Yesterday's pollutant: 30, ozone
Color codes:
Green = Good
Yellow = Moderate
100
150
200
Orange = Unhealthy for Sensitive Groups
Red = Unhealthy
Example 3. A longer form for a newspaper.
The Air Quality in Baltimore yesterday
The AIR QUALITY yesterday in
Northeast Baltimore was Unhealthy for
Sensitive Groups due to ozone. Groups
likely to be sensitive to ozone include
active children and adults, and people with
respiratory disease such as asthma. The air
quality index was 110 resulting from an
ozone concentration of 0.088 ppm.
Elsewhere in Baltimore, the air quality
index was 87 or Moderate. Since today's
air quality is expected to be much the
same, people in the sensitive groups
should limit prolonged outdoor exertion.
With outdoor exertion, these groups may
experience respiratory symptoms and
breathing discomfort.
MODERATE
UNHEALTHY for SENSITIVE GROUPS
HAZARDOUS
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The following is a short script that could be used for a television evening news/weather report. Graphics
used for the report could be similar to the graphics used in newspaper reports. You must use the
descriptors and, if a color format is used, colors for the categories that are listed in Table 1, above.
Example 4. A short form for television (evening).
"The air quality index today was 156, in the red category. Air stagnation caused a buildup of ozone
to unhealthy levels. Children and people with asthma are the groups most at risk."
Example 5. A short form for television (morning).
"Yesterday the air quality was unhealthy due to ozone, and we expect similar air quality today - in the
red range or around an index of 160 which is unhealthy. Children and people with asthma are the
groups most at risk. Active children and adults and people with asthma or other respiratory diseases
should avoid prolonged physical exertion outside today. In fact, everyone should consider limiting
the time they spend on outdoor exercise or those outside jobs..."
Example 6. A long form for television (evening).
"Air quality today was unhealthy due to ozone, with an index value of 156. Children and people with
asthma are the groups most at risk. The cool front we expected to come through here tomorrow and
blow all this ozone away isn 't going to make it, so the stagnant air will still be here, making air
quality unhealthy. Active children and adults and people with asthma or other respiratory diseases
should avoid prolonged exertion outside tomorrow. In fact, everyone should consider limiting the
time they spend on outdoor exercise or those outside jobs..."
Recorded telephone messages can be used to give more up-to-date information on the air quality. The
following example has been used.
Example 7. A script for telephone
"As of 10:00 AM the air quality index is 45 which is good or green. The responsible pollutant is
ozone."
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The newest way to report the AQI is via a publicly accessible Internet web site. Technology is available
that can make these reports almost real-time. The Ozone Mapping Project (http://www.epa.gov/airnow)
comes very close to real-time and uses much more involved analysis than is required for AQI reporting.
Examples of web site reporting are given below.
Example 8. A short form for a Web site
Air Quality Index for St. Louis, MO for July 19,1999
Time of this report:
Responsible pollutant:
Sensitive Groups
1:OOPM
Ozone
AQI:
Category:
110
Color:
Unhealthy for Sensitive Groups
Children and people with asthma are the groups most at risk.
Example 9. A long form for a Web site
Air Quality Index for Chicago, IL for August 1, 1999
Report as of:
2:00PM
AQI:
162
J Responsible pollutant: | Ozone
Color:
Category:
Unhealthy
Sensitive groups: | Children and people with asthma are the groups most at risk.
Health effects:
Greater likelihood of respiratory symptoms and breathing difficulty in sensitive groups, possible
respiratory effects in the general population.
HEALTH
ADVISORY
Active children and adults, and people with respiratory disease, such as asthma, should avoid prolonged
outdoor exertion; everyone else (especially children) should limit prolonged outdoor exertion.
Air Quality in South Chicago - Gary, IL
Tomorrow's air quality in Chicago is
predicted to be:
AQI:
122
(Unhealthy for Sensitive Groups)
Unhealthy for Sensitive Groups
Color:
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What colors do I use in my AQI report?
If you report the air quality index in a color format, the colors you must use are specified in
appendix G and Table 3, below:
Table 3. AQI Colors
For this category ... ... use this color
Good Green
Moderate Yellow
Unhealthy for Sensitive Groups Orange
Unhealthy Red
Very Unhealthy Purple
Hazardous Maroon
Suggested color formulations are defined in Table 4, below, for red, green, blue (RGB) and cyan,
magenta, yellow, and black (CMYK) color formulas:1
Table 4. Suggested AQI Color Formulas
Color2
Green
Yellow
Orange
Red
Purple
Maroon
R
0
255
255
255
153
76
G
228
255
126
0
0
0
B
0
0
0
0
76
38
C
224
0
0
0
0
0
M
0
0
132
255
153
76
Y
224
255
255
255
80
38
K
30
0
0
0
102
179
1 The RGB model is traditionally used for screen colors while CMYK is traditionally used for
printing processes.
2 The color models are based on a 0 - 255 scale (e.g. 50% is 127).
What health effects and cautionary statements should I use in my report?
The most recent health effects information used with the AQI is pollutant-specific. The
following tables list the different health effects messages, sensitive groups, and cautionary statements
for each pollutant in the AQI.
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Table 5. Pollutant-Specific Health Effects Statements for the Air Quality Index (AQI)
AQI
Category
Good
Moderate
Ozone
[8-hour]
None
Unusually sensitive
(ppm)
[1-hour]
Particulate Matter (jig/m3)
PM25 [24-hour] PM10 [24-hour]
None
None
None
None
Carbon
Monoxide
(ppm)
[8-hour]
None
None
Sulfur Dioxide
(ppm)
[24-hour]
None
None
Nitrogen
Dioxide
(ppm)
[1-hour]
None
None
Unhealthy
for
Sensitive
Groups
Unhealthy
individuals may
experience respiratory
symptoms.
Increasing likelihood
of respiratory
symptoms and
breathing discomfort
in active children and
adults and people
with respiratory
disease, such as
asthma.
Greater likelihood of
respiratory symptoms
and breathing
difficulty in active
children and adults
and people with
respiratory disease,
such as asthma;
possible respiratory
effects in general
population.
Increasing likelihood
of respiratory
symptoms and
breathing discomfort
in active children and
adults and people
with respiratory
disease, such as
asthma.
Greater likelihood of
respiratory symptoms
and breathing
difficulty in active
children and adults
and people with
respiratory disease,
such as asthma;
possible respiratory
effects in general
population.
Increasing likelihood
of respiratory
symptoms in sensitive
individuals,
aggravation of heart
or lung disease and
premature mortality in
persons with
cardiopulmonary
disease and the
elderly.
Increased aggravation
of heart or lung
disease and premature
mortality in persons
with
cardiopulmonary
disease and the
elderly; increased
respiratory effects in
general population.
Increasing likelihood
of respiratory
symptoms and
aggravation of lung
disease, such as
asthma.
Increased respiratory
symptoms and
aggravation of lung
disease, such as
asthma; possible
respiratory effects in
general population.
Increasing likelihood
of reduced exercise
tolerance due to
increased
cardiovascular
symptoms, such as
chest pain, in people
with cardiovascular
disease.
Reduced exercise
tolerance due to
increased
cardiovascular
symptoms, such as
chest pain, in people
with cardiovascular
disease.
Increasing likelihood
of respiratory
symptoms, such as
chest tightness and
breathing discomfort,
in people with
asthma.
Increased respiratory
symptoms, such as
chest tightness and
wheezing in people
with asthma; possible
aggravation of heart
or lung disease.
None
None
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Table 5. Pollutant-Specific Health Effects Statements for the Air Quality Index (AQI) (Cont.)
AQI
Category
Ozone (ppm)
[8-hour] [1-hour]
Particulate Matter (jig/m3)
PM25 [24-hour] PM10 [24-hour]
Carbon
Monoxide
(ppm)
[8-hour]
Sulfur Dioxide
(ppm)
[24-hour]
Nitrogen
Dioxide
(ppm)
[1-hour]
Very
Unhealthy
Hazardous
Increasingly severe
symptoms and
impaired breathing
likely in active
children and adults
and people with
respiratory disease,
such as asthma;
increasing likelihood
of respiratory effects
in general population.
Severe respiratory
effects and impaired
breathing likely in
active children and
adults and people
with respiratory
disease, such as
asthma; increasingly
severe respiratory
effects likely in
general population.
Increasingly severe
symptoms and
impaired breathing
likely in active
children and adults
and people with
respiratory disease,
such as asthma;
increasing likelihood
of respiratory effects
in general population.
Severe respiratory
effects and impaired
breathing likely in
active children and
adults and people
with respiratory
disease, such as
asthma; increasingly
severe respiratory
effects likely in
general population.
Significant
aggravation of heart
or lung disease and
premature mortality in
persons with
cardiopulmonary
disease and the
elderly; significant
increase in respiratory
effects in general
population.
Serious aggravation
of heart or lung
disease and premature
mortality in persons
with
cardiopulmonary
disease and the
elderly; serious risk of
respiratory effects in
general population.
Significant increase in
respiratory symptoms
and aggravation of
lung disease, such as
asthma; increasing
likelihood of
respiratory effects in
general population.
Serious risk of
respiratory symptoms
and aggravation of
lung disease, such as
asthma; respiratory
effects likely in
general population.
Significant
aggravation of
cardiovascular
symptoms, such as
chest pain, in people
with cardiovascular
disease.
Serious aggravation
of cardiovascular
symptoms, such as
chest pain, in people
with cardiovascular
disease; impairment
of strenuous activities
in general population.
Significant increase in
respiratory symptoms,
such as wheezing and
shortness of breath, in
people with asthma;
aggravation of heart
or lung disease.
Severe respiratory
symptoms, such as
wheezing and
shortness of breath, in
people with asthma;
increased aggravation
of heart or lung
disease; possible
respiratory effects in
general population.
Increasing likelihood
of respiratory
symptoms and
breathing discomfort
in children and people
with respiratory
disease, such as
asthma.
Greater likelihood of
respiratory symptoms
and breathing
difficulty in children
and people with
respiratory disease,
such as asthma.
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Table 6. Pollutant-Specific Cautionary Statements for the Air Quality Index (AQI)
AQI
Category
Ozone (ppm)
[8-hour]
[1-hour]
Particulate Matter (jig/m3)
PM2 5 [24-
hour]
PM10 [24-
hour]
Carbon
Monoxide
(ppm)
[8-hour]
Sulfur Dioxide
(ppm)
[24-hour]
Nitrogen
Dioxide
(ppm)
[1-hour]
Good
None
None
None
None
None
None
Moderate
Unhealthy
for
Sensitive
Groups
Unhealthy
Unusually sensitive
people should
consider limiting
prolonged outdoor
exertion.
Active children and
adults, and people
with respiratory
disease, such as
asthma, should limit
prolonged outdoor
exertion.
Active children and
adults, and people
with respiratory
disease, such as
asthma, should
avoid prolonged
outdoor exertion;
everyone else,
especially children,
should limit
prolonged outdoor
exertion.
None
None
None
None
None
Active children and
adults, and people
with respiratory
disease, such as
asthma, should limit
heavy outdoor
exertion.
Active children and
adults, and people
with respiratory
disease, such as
asthma, should avoid
heavy outdoor
exertion; everyone
else, especially
children, should limit
heavy outdoor
exertion.
People with
respiratory or heart
disease, the elderly
and children should
limit prolonged
exertion.
People with
respiratory or heart
disease, the elderly
and children should
avoid prolonged
exertion; everyone
else should limit
prolonged exertion.
People with
respiratory disease,
such as asthma,
should limit
outdoor exertion.
People with
cardiovascular
disease, such as
angina, should limit
heavy exertion and
avoid sources of CO,
such as heavy traffic.
People with
cardiovascular
disease, such as
angina, should limit
moderate exertion and
avoid sources of CO,
such as heavy traffic.
People with asthma
should consider
limiting outdoor
exertion.
Children, asthmatics,
and people with heart
or lung disease should
limit outdoor exertion.
None
None
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Table 6. Pollutant-Specific Cautionary Statements for the Air Quality Index (AQI) (Cont.)
AQI
Category
Very
Unhealthy
Ozone (ppm)
[8-hour]
Active children and
adults, and people
with respiratory
disease, such as
asthma, should
avoid all outdoor
exertion; everyone
else, especially
children, should
limit outdoor
exertion.
[1-hour]
Active children and
adults, and people
with respiratory
disease, such as
asthma, should avoid
all outdoor exertion;
everyone else,
especially children,
should limit outdoor
exertion.
Particulate Matter (jig/m3)
PM2 5 [24-
hour]
People with
respiratory or heart
disease, the elderly
and children should
avoid any outdoor
activity; everyone
else should avoid
prolonged exertion.
PM10 [24-hour]
People with
respiratory disease,
such as asthma,
should avoid any
outdoor activity;
everyone else,
especially the elderly
and children, should
limit outdoor
exertion.
Carbon
Monoxide
(ppm)
[8-hour]
People with
cardiovascular
disease, such as
angina, should avoid
exertion and sources
of CO, such as heavy
traffic.
Sulfur Dioxide
(ppm)
[24-hour]
Children, asthmatics,
and people with heart
or lung disease should
avoid outdoor
exertion; everyone
else should limit
outdoor exertion.
Nitrogen
Dioxide
(ppm)
[1-hour]
Children and people
with respiratory
disease, such as
asthma, should limit
heavy outdoor
exertion.
Hazardous
Everyone should
avoid all outdoor
exertion.
Everyone should
avoid all outdoor
exertion.
Everyone should
avoid any outdoor
exertion; people
with respiratory or
heart disease, the
elderly and children
should remain
indoors.
Everyone should
avoid any outdoor
exertion; people with
respiratory disease,
such as asthma,
should remain
indoors.
People with
cardiovascular
disease, such as
angina, should avoid
exertion and sources
of CO, such as heavy
traffic; everyone else
should limit heavy
exertion.
Children, asthmatics,
and people with heart
or lung disease should
remain indoors;
everyone else should
avoid outdoor
exertion.
Children and people
with respiratory
disease, such as
asthma, should limit
moderate or heavy
outdoor exertion.
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How do I calculate the AQI from pollutant concentration data?
You calculate the AQI by using your pollutant concentration data, the breakpoints in Table 7 on
the next page, and the following equation (linear interpolation):
Equation 1
T _ Hi Lo /p _ DD \+T
% nn nn ^ P DrLcJ^ ko"
Where Ip = the index for pollutant p
Cp = the rounded concentration of pollutant p
BPK = the breakpoint that is greater than or equal to Cp
BP^ = the breakpoint that is less than or equal to Cp
IK = the AQI value corresponding to BPK
Ilo = the AQI value corresponding to
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Table 7. Breakpoints for the AQI
These Breakpoints
equal these AQIs...
O3 (ppm) O3 (ppm) PM2 5
8-hour 1-hour1 (u,g/m3)
0.000-0.064 - 0.0 -
0.065-0.084 - 15.5-
0.085-0.104 0.125-0.164 40.5-
0.105-0.124 0.165-0.204 65.5-
0.125-0.374 0.205-0.404 150.5-
(3) 0.405-0.504 250.5-
(3) 0.505-0.604 350.5-
15.4
40.4
65.4
150.4
250.4
350.4
500.4
PM10
0
55
155
255
355
425
505
-54
-154
-254
-354
-424
-504
-604
CO (ppm)
0.0-
4.5-
9.5-
12.5-
15.5-
30.5-
40.5-
4.4
9.4
12.4
15.4
30.4
40.4
50.4
SO2
0.000
0.035
0.145
0.225
0.305
0.605
0.805
(ppm)
Category
NO2 (ppm) AQI
- 0.034 (2) 0
-0,
-0,
-0.
-0,
-0,
-1
.144
.224
304
.604
.804
.004
(2) 51
(2) 101
(2) 151
0.65-1.24 201
1.25-1.64 301
1.65-2.04 401
-50
-100
-150
-200
-300
-400
-500
Good
Moderate
Unhealthy for
sensitive groups
Unhealthy
Very unhealthy
Hazardous
1 Areas are generally required to report the AQI based on 8-hour ozone values. However, there are a small number of areas where an AQI based on 1-hour ozone values would be more
precautionary. In these cases, in addition to calculating the 8-hour ozone index value, the 1-hour ozone index value may be calculated and the maximum of the two values is reported.
2 NO2 has no short-term NAAQS and can generate a AQI only above a AQI value of 200.
3 When 8-hour O3 concentrations exceed 0.374 ppm, AQI values of 301 or higher must be calculated with 1-hour O3 concentrations.
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Example 1. 8-hour Ozone.
Suppose you have an 8-hour ozone concentration of 0.0875125 ppm. First you truncate the
concentration to 0.087 ppm. Then you look in Table 7 under 8-hour ozone for the range of
concentrations that contain this concentration (0.085 - 0.104 ppm). This range in the table for 8-hour
ozone corresponds to index values of 101 to 150. Now you have all the numbers needed to use the
equation:
(101-150) 49
-0-085)+ 101 = — 0.002 + 101 = 106.157 = 106
So an 8-hour concentration of 0.0875125 corresponds to an index value of 106.
Example 2. Multiple pollutants.
Suppose you have an 8-hour ozone value of 0.077 ppm, a PM2 5 value of 54.4 |ig/m3, and a CO value of
8.4 ppm. You apply the equation 3 times:
(100-51)
°3' (0.084-0.065)(
(150-101)
(65.4- 40.5)
(54.4 -40.5) + 101 = 128
v ;
The AQI is 128 with PM2 5 as the responsible pollutant.
Example 3. Ozone 1-hour and Ozone 8-hour concentrations.
Suppose you had a 1-hour concentration of 0.162 ppm and an 8-hour concentration of 0.141125 ppm.
Then you apply the equation twice:
(150-101)
'-^
0.164-0.125)v
(300-201)
(0.374-0.125)^
14
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In this case, the index is 207 (the maximum of 147 and 207) and the responsible pollutant is ozone (8-
hour).
Example 4. PM25 andPM10 concentrations.
Suppose you had daily concentrations of PM25 (48.7 |ig/m3) and PM10 (178 |ig/m3). Then you apply
Equation 1 twice as if you had two pollutants instead of two indicators of the same pollutant:
(150-101)
'
In this case the AQI would be 1 17 (the maximum of 1 17 and 112) and the responsible pollutant would be
PM (PM25).
Example 5. Concentrations for pollutants that have blank places in Table 7
You disregard 8-hour ozone concentrations greater than 0.374 ppm, 1-hour ozone concentrations
less than 0.125 ppm, and NO2 concentrations less than 0.65 ppm. Suppose you had a 1-hour ozone
concentration of 0.104 ppm, an 8-hour ozone concentration of 0.087 ppm and an NO2 concentration of
0.54 ppm. First you disregard the 1-hour ozone concentration because it is less than 0. 125 ppm and the
NO2 concentration because it is less than 0.65 ppm. Then you calculate the index for the 8-hour ozone
concentration as before:
(150-101)
(0.087 -0.085) + 101 = 106.1 58
v ;
(0.104-0.085)
which rounds to an AQI value of 106.
Are there exceptions to these reporting requirements?
Yes. When you have low index values that meet the following criteria, you do not have to meet
all the requirements:
• If the index for a specific pollutant remains below 50 for a season or a year, then you are not
required to include this pollutant in the calculation of the AQI.
• If your calculated AQI remains below 50 for more than a year, then you are not required to report
the AQI.
15
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However, if any of these conditions are not met in subsequent years, then you must resume
reporting the index according to Appendix G to Part 58 of 40 CFR.
Where do I get the pollutant concentrations for the AQI?
The pollutant concentration data is from the State and Local Air Monitoring Stations (SLAMS)
operating under the rules set forth in Part 58 of 40 CFR. You are not required to have any special
monitors in your area for the purpose of reporting the AQI. In the case of PM, many areas use non-
Federal Reference Method monitors (continuous PM monitors such as TEOM monitors) for the purpose
of reporting the AQI. The EPA encourages you to do this for the sake of timely reporting of the AQI. It
is only necessary for you to establish a linear relationship between concentrations from a Federal
Reference or Equivalent Method and a non-reference method monitor for the purpose of reporting PM
values in the AQI.
Where do I find more information about reporting the AQI?
There are several publications, guidance documents, and a computer program to help you report
the AQI. These may be found on the AIRNOW web site or from the AIR
QUALITY TRENDS ANALYSIS GROUP, US EPA (MD-14), RTF, NC 27711.
• Ozone health effects booklet and pamphlet
• AQI brochure
• AQI calculator program
• Forecasting guidance
Do I have to forecast pollutant concentrations for the AQI report?
You are not required to forecast, but if you choose to do so, we encourage you to forecast values
24 hours in advance. The AQI is designed to inform the public about air quality so that individuals may
choose to avoid exposure to certain levels and types of air pollution. This choice is unavailable if the
information is not timely. Forecasts caution people in advance. However, good forecasts require data,
computational resources and expertise that may be unavailable to you. The EPA provides guidance if
you are interested in starting a forecasting program for your MSA.
Since ozone is often the critical pollutant in AQI reporting and the averaging period is 8 hours,
informing the public before the end of the maximum 8-hour period is important even if you are not able
to forecast 24 hours in advance. In order for individuals to take advantage of this information, it is
necessary to consider at least a short term forecast or prediction of 8-hour ozone levels for the purposes
of reporting the AQI. You can do this with very little additional resources. You can rely on the high
correlation between daily maximum values of 8-hour and 1-hour ozone concentrations. A simple linear
regression can be calculated on daily maximum data at any site. From this regression, you can predict
that the 8-hour ozone maximum for a day will be at least as high as the 8-hour value corresponding to the
present 1-hour value. From this information you can predict the AQI hours earlier than if you wait for
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the full 8-hour maximum to be observed.
What if the correlation at my site is low?
The lowest observed correlation between 1-hour and 8-hour maximum ozone concentrations at
any site reporting to AIRS data was 0.86. This correlation is adequate to predict the maximum 8-hour
values from the maximum 1-hour values for reporting the AQI. However, if you feel uncomfortable due
to the imprecision from lower correlations, you may want to predict the AQI from the confidence interval
for the 8-hour maximum predicted from the 1-hour maximum. In other words, if your are more
concerned about "false negatives," for example, not predicting unhealthy air quality when the
concentrations later in the day might reach unhealthy levels, then predict unhealthy air quality as soon as
the upper bound of the confidence interval is greater than the AQI breakpoint for the unhealthy category.
If you are more concerned about "false positives," for example, predicting unhealthy air quality when the
concentrations later in the day might indicate that air quality did not reach unhealthy levels, then you
should consider predicting unhealthy air quality only when the lower bound of the confidence interval is
above the breakpoint for the unhealthy category.
How do I calculate the upper and lower bounds for the confidence interval for the predicted
maximum 8-hour ozone value?
Most computer regression programs include the error variance or the residual variance or the
variance of "Y given X" as part of the output. Call this Se2. Then you calculate the upper an lower
bounds of the predicted value as:
Where:
^is the predicted 8-hour ozone maximum,
ti-B/2,n-2 i§ a tabulated Student's-T value corresponding to a two sided (1- cc)100% confidence
interval with n-2 degrees of freedom,
Se2 is the error variance described above,
x' is the 1-hour value used to predict the 8-hour value,
1 is the average of the 1-hour values, and
Sx2 is the variance of the 1-hour values.
The value a is arbitrary, but conventionally it is usually set to 0.05 corresponding to a 95% confidence
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interval.
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APPENDIX
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Table A-l. Metropolitan Statistical Areas with over 350,000 population (1990 Census)
MSA NAME POPULATION
80 AKRON, OH 657,575
160 ALBANY-SCHENECTADY-TROY, NY 861,424
200 ALBUQUERQUE, NM 589,131
240 ALLENTOWN-BETHLEHEM-EASTON, PA 595,081
440 ANN ARBOR, MI 490,058
520 ATLANTA, GA 2,959,950
600 AUGUSTA-AIKEN, GA-SC 415,184
620 AURORA-ELGIN, IL 356,884
640 AUSTIN-SAN MARCOS, TX 846,227
680 BAKERSFIELD, CA 543,477
720 BALTIMORE, MD 2,382,172
760 BATON ROUGE, LA 528,264
840 BEAUMONT-PORT ARTHUR, TX 361,226
875 BERGEN-PASSAIC, NJ 1,278,440
1000 BIRMINGHAM, AL 840,140
1120 BOSTON, MA-NH 3,227,707
1160 BRIDGEPORT, CT 443,722
1280 BUFFALO-NIAGARA FALLS, NY 1,189,288
1320 CANTON-MASSILLON, OH 394,106
1440 CHARLESTON-NORTH CHARLESTON, SC 506,875
1520 CHARLOTTE-GASTONIA-ROCK HILL, NC-SC 1,162,093
1560 CHATTANOOGA, TN-GA 424,347
1600 CHICAGO, IL 7,410,858
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MSA NAME POPULATION
1640 CINCINNATI, OH-KY-IN 1,526,092
1680 CLEVELAND-LORAIN-ELYRIA, OH 2,202,069
1720 COLORADO SPRINGS, CO 397,014
1760 COLUMBIA, SC 453,331
1840 COLUMBUS, OH 1,345,450
1920 DALLAS, TX 2,676,248
1960 DAVENPORT-MOLINE-ROCK ISLAND, IA-IL 350,861
2000 DAYTON-SPRINGFIELD, OH 951,270
2020 DAYTONA BEACH, FL 399,413
2080 DENVER, CO 1,622,980
2120 DES MOINES, IA 392,928
2160 DETROIT, MI 4,266,654
2320 EL PASO, TX 591,610
2640 FLINT, MI 430,459
2680 FORT LAUDERDALE, FL 1,255,488
2760 FORT WAYNE, IN 456,281
2800 FORT WORTH-ARLINGTON, TX 1,361,034
2840 FRESNO, CA 755,580
2960 GARY, IN 604,526
3000 GRAND RAPIDS-MUSKEGON-HOLLAND, MI 937,891
3120 GREENSBORO-WINSTON-SALEM-HIGH POINT, NC 1,050,304
3160 GREENVILLE-SPARTANBURG-ANDERSON, SC 830,563
3240 HARRISBURG-LEBANON-CARLISLE, PA 587,986
3280 HARTFORD, CT 1,157,585
3320 HONOLULU, HI 836,231
3360 HOUSTON, TX 3,322,025
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MSA NAME POPULATION
3480 INDIANAPOLIS, IN 1,380,491
3560 JACKSON, MS 395,396
3600 JACKSONVILLE, FL 906,727
3640 JERSEY CITY, NJ 553,099
3660 JOHNSON CITY-KINGSPORT-BRISTOL, TN-VA 436,047
3720 KALAMAZOO-BATTLE CREEK, MI 429,453
3760 KANSAS CITY, MO-KS 1,582,875
3840 KNOXVILLE, TN 585,960
3980 LAKELAND-WINTER HAVEN, FL 405,382
4000 LANCASTER, PA 422,822
4040 LANSING-EAST LANSING, MI 432,674
4120 LAS VEGAS, NV-AZ 852,737
4160 LAWRENCE, MA-NH 353,232
4280 LEXINGTON, KY 405,936
4400 LITTLE ROCK-NORTH LITTLE ROCK, AR 513,117
4480 LOS ANGELES-LONG BEACH, CA 8,863,164
4520 LOUISVILLE, KY-IN 948,829
4720 MADISON, WI 367,085
4880 MCALLEN-EDINBURG-MISSION, TX 383,545
4900 MELBOURNE-TITUSVILLE-PALM BAY, FL 398,978
4920 MEMPHIS, TN-AR-MS 1,007,306
5000 MIAMI, FL 1,937,094
5015 MIDDLESEX-SOMERSET-HUNTERDON, NJ 1,019,835
5080 MILWAUKEE-WAUKESHA, WI 1,432,149
5120 MINNEAPOLIS-ST. PAUL, MN-WI 2,538,834
5160 MOBILE, AL 476,923
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MSA NAME POPULATION
5170 MODESTO, CA 370,522
5190 MONMOUTH-OCEAN, NJ 986,327
5360 NASHVILLE, TN 985,026
5380 NASSAU-SUFFOLK, NY 2,609,212
5480 NEW HAVEN-MERIDEN, CT 530,180
5560 NEW ORLEANS, LA 1,285,270
5600 NEW YORK, NY 8,546,846
5640 NEW ARK, NJ 1,915,928
5720 NORFOLK-VIRGINIA BEACH-NEWPORT NEWS,VA-NC 1,443,244
5775 OAKLAND, CA 2,082,914
5880 OKLAHOMA CITY, OK 958,839
5920 OMAHA, NE-IA 639,580
5945 ORANGE COUNTY, CA 2,410,556
5960 ORLANDO, FL 1,224,852
6160 PHILADELPHIA, PA-NJ 4,922,175
6200 PHOENIX-MESA, AZ 2,238,480
6280 PITTSBURGH, PA 2,384,811
6360 PONCE, PR 3,442,660
6440 PORTLAND-VANCOUVER, OR-WA 1,515,452
6480 PROVIDENCE-FALL RIVER-WARWICK, RI-MA 1,134,350
6640 RALEIGH-DURHAM-CHAPEL HILL, NC 855,545
6760 RICHMOND-PETERSBURG, VA 865,640
6780 RIVERSIDE-SAN BERNARDINO, CA 2,588,793
6840 ROCHESTER, NY 1,062,470
6920 SACRAMENTO, CA 1,340,010
6960 SAGINAW-BAY CITY-MIDLAND, MI 399,320
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MSA NAME POPULATION
7040 ST. LOUIS, MO-IL 1,836,302
7120 SALINAS, CA 355,660
7160 SALT LAKE CITY-OGDEN, UT 1,072,227
7240 SAN ANTONIO, TX 1,324,749
7320 SAN DIEGO, CA 2,498,016
7360 SAN FRANCISCO, CA 1,603,678
7400 SAN JOSE, CA 1,497,577
7440 SAN JUAN-BAYAMON, PR 1,836,302
7480 SANTA BARBARA-SANTA MARIA-LOMPOC, CA 369,608
7500 SANTA ROSA, CA 388,222
7510 SARASOTA-BRADENTON, FL 489,483
7560 SCRANTON-WILKES-BARRE-HAZLETON, PA 638,466
7600 SEATTLE-BELLEVUE-EVERETT, WA 2,033,156
7680 SHREVEPORT-BOSSIER CITY, LA 376,330
7840 SPOKANE, WA 361,364
8000 SPRINGFIELD, MA 587,884
8120 STOCKTON-LODI, CA 480,628
8160 SYRACUSE, NY 742,177
8200 TACOMA, WA 586,203
8280 TAMPA-ST. PETERSBURG-CLEARWATER, FL 2,067,959
8400 TOLEDO, OH 614,128
8520 TUSCON, AZ 666,880
8560 TULSA, OK 708,954
8720 VALLEJO-F AIRFIELD-NAP A, C A 451,186
8735 VENTURA, CA 669,016
8840 WASHINGTON, DC-MD-VA-WV 4,223,485
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MSA NAME POPULATION
8960 WEST PALM BEACH-BOCA RATON, FL 863,518
9040 WICHITA, KS 485,270
9160 WILMINGTON-NEWARK, DE-MD 513,293
9240 WORCESTER, MA-CT 478,384
9320 YOUNGSTOWN-WARREN, OH 600,859
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