EPA

Office of Air Quality

Pla nnin g a nd S ta nd a rds

C Air

lean

United States Office of Air Quality EPA-454/R-99-010

Environmental Protection Planning and Standards July 1999

Agency Research Triangle Park, NC 27711

Air

GUIDELINE FOR REPORTING OF

DAILY AIR QUALITY - AIR QUALITY

INDEX (AQI)

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
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. 
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-1 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 realtime 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
 A recorded phone message or a radio broadcast cannot show colors but can name a color in the report 1

(e.g., this is a category “red” day).

 Suggested color formulations are given in Table 4. 2

2

 The category descriptor and, if reported in a color format, the associated color. Use only the 1

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

201 to 300 .............................. “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.

PM People with respiratory or heart disease, the 2.5

elderly and children are the groups most at risk.

PM People with respiratory disease are the group 10

most at risk.

CO People with heart disease are the group most at

risk.

SO People with asthma are the group most at risk. 2
3

NO Children and people with respiratory disease are 2

the groups most at risk.

An AQI report may also contain:

 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.



GOOD

MODERATE

UNHEALTHY for SENSITIVE GROUPS

UNHEALTHY

VERY UNHEALTHY

HAZARDOUS
4

Example 2. A short form for a newspaper in black and white.

Air Quality for Washington, D.C.

 Today’s forecast Yesterday

Air Quality Index (AQI)

 

Green Yellow Orange Red

 | | | | |

 0 50 100 150 200

Yesterday’s pollutant : 30, ozone

Color codes: 

Green = Good Orange = Unhealthy for Sensitive Groups

Yellow = Moderate 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.



GOOD

MODERATE

UNHEALTHY for SENSITIVE GROUPS

UNHEALTHY

VERY UNHEALTHY

HAZARDOUS
5

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.”
6

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: AQI: Color: 1:00PM 110 Orange

Responsible pollutant: Category: Ozone Unhealthy for Sensitive Groups

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: AQI: Responsible pollutant: 2:00PM 162 Ozone

 Color: Category: Red 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 AQI: 122 (Unhealthy for Sensitive Groups)

Tomorrow’s air quality in Chicago is Unhealthy for Sensitive Groups Color: Orange

predicted to be:
7

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

Color R G B C M Y K 2

Green 0 228 0 224 0 224 30

Yellow 255 255 0 0 0 255 0

Orange 255 126 0 0 132 255 0

Red 255 0 0 0 255 255 0

Purple 153 0 76 0 153 80 102

Maroon 76 0 38 0 76 38 179

 The RGB model is traditionally used for screen colors while CMYK is traditionally used for 1

printing processes.

 The color models are based on a 0 - 255 scale (e.g. 50% is 127). 2

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.
8

Table 5. Pollutant-Specific Health Effects Statements for the Air Quality Index (AQI)

AQI Ozone (ppm) Particulate Matter (μg/m ) Carbon Sulfur Dioxide Nitrogen

Category Monoxide (ppm) Dioxide

3

(ppm) [24-hour] (ppm)

[8-hour] [1-hour] [8-hour] [1-hour] PM [24-hour] PM [24-hour] 2.5 10

Good None None None None None None

Moderate Unusually sensitive None None None None None

individuals mayexperience respiratorysymptoms.

Unhealthy Increasing likelihood Increasing likelihood Increasing likelihood Increasing likelihood Increasing likelihood Increasing likelihood None

for of respiratory of respiratory of respiratory of respiratory of reduced exercise of respiratory

Sensitive symptoms and symptoms and symptoms in sensitive symptoms and tolerance due to symptoms, such as

Groups breathing discomfort breathing discomfort individuals, aggravation of lung increased chest tightness and

in active children and in active children and aggravation of heart disease, such as cardiovascular breathing discomfort,adults and people adults and people or lung disease and asthma. symptoms, such as in people withwith respiratory with respiratory premature mortality in chest pain, in people asthma.disease, such as disease, such as persons with with cardiovascularasthma. asthma. cardiopulmonary disease.

disease and theelderly.

Unhealthy Greater likelihood of Greater likelihood of Increased aggravation Increased respiratory Reduced exercise Increased respiratory None

respiratory symptoms respiratory symptoms of heart or lung symptoms and tolerance due to symptoms, such asand breathing and breathing disease and premature aggravation of lung increased chest tightness anddifficulty in active difficulty in active mortality in persons disease, such as cardiovascular wheezing in peoplechildren and adults children and adults with asthma; possible symptoms, such as with asthma; possibleand people with and people with cardiopulmonary respiratory effects in chest pain, in people aggravation of heartrespiratory disease, respiratory disease, disease and the general population. with cardiovascular or lung disease.such as asthma; such as asthma; elderly; increased disease.possible respiratory possible respiratory respiratory effects ineffects in general effects in general general population.population. population.
9

Table 5. Pollutant-Specific Health Effects Statements for the Air Quality Index (AQI) (Cont.)

AQI Ozone (ppm) Particulate Matter (μg/m ) Carbon Sulfur Dioxide Nitrogen

Category Monoxide (ppm) Dioxide

3

(ppm) [24-hour] (ppm)

[8-hour] [1-hour] [8-hour] [1-hour] PM [24-hour] PM [24-hour] 2.5 10

Very Increasingly severe Increasingly severe Significant Significant increase in Significant Significant increase in Increasing likelihood

Unhealthy symptoms and symptoms and aggravation of heart respiratory symptoms aggravation of respiratory symptoms, of respiratory

impaired breathing impaired breathing or lung disease and and aggravation of cardiovascular such as wheezing and symptoms andlikely in active likely in active premature mortality in lung disease, such as symptoms, such as shortness of breath, in breathing discomfort

children and adults children and adults persons with asthma; increasing chest pain, in people people with asthma; in children and peopleand people with and people with cardiopulmonary likelihood of with cardiovascular aggravation of heart with respiratoryrespiratory disease, respiratory disease, disease and the respiratory effects in disease. or lung disease. disease, such assuch as asthma; such as asthma; elderly; significant general population. asthma.increasing likelihood increasing likelihood increase in respiratoryof respiratory effects of respiratory effects effects in generalin general population. in general population. population.

Hazardous Severe respiratory Severe respiratory Serious aggravation Serious risk of Serious aggravation Severe respiratory Greater likelihood of

effects and impaired effects and impaired of heart or lung respiratory symptoms of cardiovascular symptoms, such as respiratory symptomsbreathing likely in breathing likely in disease and premature and aggravation of symptoms, such as wheezing and and breathingactive children and active children and mortality in persons lung disease, such as chest pain, in people shortness of breath, in difficulty in children

adults and people adults and people with asthma; respiratory with cardiovascular people with asthma; and people withwith respiratory with respiratory cardiopulmonary effects likely in disease; impairment increased aggravation respiratory disease,disease, such as disease, such as disease and the general population. of strenuous activities of heart or lung such as asthma.asthma; increasingly asthma; increasingly elderly; serious risk of in general population. disease; possiblesevere respiratory severe respiratory respiratory effects in respiratory effects ineffects likely in effects likely in general population. general population.general population. general population.
10

Table 6. Pollutant-Specific Cautionary Statements for the Air Quality Index (AQI)

AQI Ozone (ppm) Particulate Matter (μg/m ) Carbon Sulfur Dioxide Nitrogen

Category Monoxide (ppm) Dioxide

3

(ppm) [24-hour] (ppm)

[8-hour] [1-hour] [8-hour] [1-hour] PM [24- PM [24- 2.5 hour] hour] 10

Good None None None None None None

Moderate Unusually sensitive None None None None None

people shouldconsider limitingprolonged outdoorexertion.

Unhealthy Active children and Active children and People with People with People with People with asthma None

for adults, and people adults, and people respiratory or heart respiratory disease, cardiovascular should consider

Sensitive with respiratory with respiratory disease, the elderly such as asthma, disease, such as limiting outdoor

Groups disease, such as disease, such as and children should should limit angina, should limit exertion.

asthma, should limit asthma, should limit limit prolonged outdoor exertion. heavy exertion andprolonged outdoor heavy outdoor exertion. avoid sources of CO,exertion. exertion. such as heavy traffic.

Unhealthy Active children and Active children and People with People with Children, asthmatics, None

adults, and people adults, and people respiratory or heart cardiovascular and people with heartwith respiratory with respiratory disease, the elderly disease, such as or lung disease shoulddisease, such as disease, such as and children should angina, should limit limit outdoor exertion.asthma, should asthma, should avoid avoid prolonged moderate exertion andavoid prolonged heavy outdoor exertion; everyone avoid sources of CO,outdoor exertion; exertion; everyone else should limit such as heavy traffic.everyone else, else, especially prolonged exertion.especially children, children, should limitshould limit heavy outdoorprolonged outdoor exertion.exertion.
11

Table 6. Pollutant-Specific Cautionary Statements for the Air Quality Index (AQI) (Cont.)

AQI Ozone (ppm) Particulate Matter (μg/m ) Carbon Sulfur Dioxide Nitrogen

Category Monoxide (ppm) Dioxide

3

(ppm) [24-hour] (ppm)

[8-hour] [1-hour] [8-hour] [1-hour] PM [24- PM [24-hour] 2.5 hour] 10

Very Active children and Active children and People with People with People with Children, asthmatics, Children and people

Unhealthy adults, and people adults, and people respiratory or heart respiratory disease, cardiovascular and people with heart with respiratory

with respiratory with respiratory disease, the elderly such as asthma, disease, such as or lung disease should disease, such asdisease, such as disease, such as and children should should avoid any angina, should avoid avoid outdoor asthma, should limitasthma, should asthma, should avoid avoid any outdoor outdoor activity; exertion and sources exertion; everyone heavy outdooravoid all outdoor all outdoor exertion; activity; everyone everyone else, of CO, such as heavy else should limit exertion.exertion; everyone everyone else, else should avoid especially the elderly traffic. outdoor exertion.else, especially especially children, prolonged exertion. and children, shouldchildren, should should limit outdoor limit outdoorlimit outdoor exertion. exertion.exertion.

Hazardous Everyone should Everyone should Everyone should Everyone should People with Children, asthmatics, Children and people

avoid all outdoor avoid all outdoor avoid any outdoor avoid any outdoor cardiovascular and people with heart with respiratoryexertion. exertion. exertion; people exertion; people with disease, such as or lung disease should disease, such as

with respiratory or respiratory disease, angina, should avoid remain indoors; asthma, should limitheart disease, the such as asthma, exertion and sources everyone else should moderate or heavyelderly and children should remain of CO, such as heavy avoid outdoor outdoor exertion.should remain indoors. traffic; everyone else exertion.indoors. should limit heavy

exertion.
I 

I I

BP BP (C BP ) I . p

Hi Lo

HI Lo

= p Lo Lo

−

− − +

12

Equation 1

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):

Where I = the index for pollutant p p

 C = the rounded concentration of pollutant p p

 BP = the breakpoint that is greater than or equal to C Hi p

 BP = the breakpoint that is less than or equal to C Lo p

 I = the AQI value corresponding to BP Hi Hi

 I = the AQI value corresponding to BP . lo Lo
13

Table 7. Breakpoints for the AQI

These Breakpoints equal these AQIs... Category

O (ppm) O (ppm) PM PM CO (ppm) SO (ppm) NO (ppm) AQI 3

8-hour 1-hour (μg/m ) (μg/m )

3

1

2.5

3

10

3

2 2

0.000-0.064 - 0.0 - 15.4 0 - 54 0.0 - 4.4 0.000 - 0.034 ( ) 0 - 50 Good 20.065-0.084 - 15.5 - 40.4 55 - 154 4.5 - 9.4 0.035 - 0.144 ( ) 51 - 100 Moderate 20.085-0.104 0.125-0.164 40.5 - 65.4 155 - 254 9.5 - 12.4 0.145 - 0.224 ( ) 101 - 150 Unhealthy for 2

sensitive groups

0.105-0.124 0.165 - 0.204 65.5 - 150.4 255 - 354 12.5 - 15.4 0.225 - 0.304 ( ) 151 - 200 Unhealthy 2

0.125-0.374 0.205- 0.404 150.5 - 250.4 355 - 424 15.5 - 30.4 0.305 - 0.604 0.65 - 1.24 201 - 300 Very unhealthy

( ) 0.405- 0.504 250.5 - 350.4 425 - 504 30.5 - 40.4 0.605 - 0.804 1.25 - 1.64 301 - 400 3

Hazardous

( ) 0.505- 0.604 350.5 - 500.4 505 - 604 40.5 - 50.4 0.805 - 1.004 1.65 - 2.04 401 - 500 3

 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 1

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.

 NO has no short-term NAAQS and can generate a AQI only above a AQI value of 200. 2 2

 When 8-hour O concentrations exceed 0.374 ppm, AQI values of 301 or higher must be calculated with 1-hour O concentrations. 3 3 3
( )

(. . ) (. . ) . . . 101 1500 104 085 0 087 0 085 101

4 9

0 019 0 002 101 106 157 106 −

− − += += =

0

100 51

0 084 0 065 0 077 0 065 51 82

150 101

65 4 40 5

54 4 40 5 101 128

100 51

94 45 8 4 4 5 51 90

3

2 5

:

( )

(. . ) (. . )

:

( )

( . .) ( . .)

:

( )

( . .) (. .)

.

−

− − +=

−

− − +=

−

− − +=

P M

C O

1

150 101

0164 0125 0162 0125 101 147

8

300 201

0 374 0125 0141 0125 201 207

− −

− − +=

− −

− − +=

h r

h r

:

( )

. .) (. . )

:

( )

(. . ) (. . )

14

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:

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 PM value of 54.4 μg/m , and a CO value of 2.5

3

8.4 ppm. You apply the equation 3 times:

The AQI is 128 with PM as the responsible pollutant. 2.5

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:
P M

P M

2 5

1 0

150 101

65 4 40 5

48 7 40 5 101 117

150 101

254 155 178 155 101 112

. :

( )

( . .) ( . .)

:

( )

( ) ( )

−

− − +=

−

− − +=

( )

(. . ) (. . ) .

150 101

0104 0 085 0 087 0 085 101 106158 −

− − +=

15

In this case, the index is 207 (the maximum of 147 and 207) and the responsible pollutant is ozone (8-

hour).

Example 4. PM and PM concentrations. 2.5 10

Suppose you had daily concentrations of PM (48.7 μg/m ) and PM (178 μg/m ). Then you apply 2.5 10

3 3

Equation 1 twice as if you had two pollutants instead of two indicators of the same pollutant:

In this case the AQI would be 117 (the maximum of 117 and 112) and the responsible pollutant would be

PM (PM ). 2.5

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 NO concentrations less than 0.65 ppm. Suppose you had a 1-hour ozone 2

concentration of 0.104 ppm, an 8-hour ozone concentration of 0.087 ppm and an NO concentration of 2

0.54 ppm. First you disregard the 1-hour ozone concentration because it is less than 0.125 ppm and the

NO concentration because it is less than 0.65 ppm. Then you calculate the index for the 8-hour ozone 2

concentration as before:

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.
16

• 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 nonFederal 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 (http://www.epa.gov/airnow) or from the AIR

QUALITY TRENDS ANALYSIS GROUP, US EPA (MD-14), RTP, 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
upper Y t S

n

x x

n S

lower Y t S

n

x x

n S

n e

x

n e

x

: ∃ ( )

( )

: ∃ ( )

( )

/ ,

'

/ ,

'

+ ++ −

−





 





− ++ −

−





 





− −

− −

1 22

2

2

2

1 22

2

2

2

1

1

1

1

1

1

α

α

Y∃

x

17

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 S . Then you calculate the upper an lower e

2

bounds of the predicted value as:

Where:

is the predicted 8-hour ozone maximum,

t is a tabulated Student’s-T value corresponding to a two sided (1- 1-/2,n-2 )100% confidence

interval with n-2 degrees of freedom,

S is the error variance described above, e

2

x is the 1-hour value used to predict the 8-hour value,

 is the average of the 1-hour values, and

S is the variance of the 1-hour values. x

2

The value  is arbitrary, but conventionally it is usually set to 0.05 corresponding to a 95% confidence
18

interval.
19

APPENDIX
20

Table A-1. 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
MSA NAME POPULATION

21

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
MSA NAME POPULATION

22

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
MSA NAME POPULATION

23

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 NEWARK, 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
MSA NAME POPULATION

24

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-FAIRFIELD-NAPA, CA 451,186

8735 VENTURA, CA 669,016

8840 WASHINGTON, DC-MD-VA-WV 4,223,485
MSA NAME POPULATION

25

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