Technical Assistance Document

for the Reporting of Daily Air Quality –

the Air Quality Index (AQI)

 
EPA-454/B-13-001

December 2013

Technical Assistance Document

for the Reporting of Daily Air Quality –

the Air Quality Index (AQI)

Contact: 

David Mintz

U.S. Environmental Protection Agency

Research Triangle Park, North Carolina

U.S. Environmental Protection Agency

Office of Air Quality Planning and Standards

Research Triangle Park, North Carolina 27711
TABLE OF CONTENTS

Reporting Guidance.................................................................. 1 

Table 1: Pollutant-Specific Groups................................................2

Pollutant-Specific Health Effects Statements .................................. 8

Pollutant-Specific Sub-indices and

Cautionary Statements ..............................................................10

Table 2: Breakpoints for the AQI ...................................................14

Table 3: Metropolitan Statistical Areas.......................................... 20

Frequently Asked Questions....................................................... 23
1

This guidance is designed to aid local agencies in reporting the air quality using the Air Quality Index 

(AQI) as required in Part 58.50 of 40 CFR and according to Appendix G to Part 58 of 40 CFR.

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 

metropolitan areas with a population of more than 350,000.

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 five 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 may distribute the report to the local media (newspapers, radio, television), provide a recorded 

telephone message, or publish the report on a publicly accessible Internet site. Other efforts, 

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 be used to meet reporting requirements. 

What is in my AQI report?

Your AQI report must contain:

• The reporting area(s),

• The reporting period,

• The critical pollutant,

• The AQI, 

• 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:

For this AQI.... use this descriptor... and this color

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 above ....................................“Hazardous” Maroon

• Statements cautioning sensitive groups for all pollutants with an index value over 100. 

Use Table 1 on page on the following page to caution sensitive groups. Statements 

may be combined so that each group is mentioned only once.

 1 Although a recorded phone message or a radio broadcast can’t show colors, it can name a 

color in the report (e.g. this is a “red” air quality day).
2

Table 1: Pollutant Specific Sensitive Groups

When this pollutant has an index above 100... Report these Sensitive Groups

Ozone People with lung disease, children, older adults, and

 people who are active outdoors are the groups most 

 at risk

 

PM2.5 People with heart or lung disease, older adults,

children, and people of lower socioeconomic status 

(SES) are the groups most at risk

PM10 People with heart or lung disease, older adults, 

children, and people of lower socioeconomic status 

are the groups most at risk

CO People with heart disease are the group most at risk

NO2 People with asthma, children, and older adults are 

the groups most at risk

 

SO2 People with asthma, children, and older adults are 

the groups most at risk 

An AQI report may also contain, but does not require:

• 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” health effects and cautionary information for more than one 

pollutant, if there is more than one pollutant with an index value greater than 100.

It is important to inform the public when the AQI is above 100. This is why EPA strengthened the 

reporting provisions in section 6 of Appendix G in 1999. In particular, whenever the AQI exceeds 100, 

reporting agencies should expand reporting to all major news media, and at a minimum, should 

include notification to the media with the largest market coverage for the area in question.
3

What does an AQI report look like?

NEWSPAPER

Example 1. Newspaper short form in color

Air Quality for Raleigh, N.C.

Air Quality Index

Yesterday’s report: 66

Main pollutant: Particulate Matter

▼

0-50 

Good

51-100

Moderate

101-150

Unhealthy,

Sensitive 

groups

151-200

Unhealthy

201-300

Very

unhealthy

 ▲

Today’s ozone forecast : 38

Example 2. Newspaper short form in black and white

Chicago Tribune

AIR QUALITY

Illinois EPA’s air quality index (AQI):

0-50 is good; 51-100 moderate; 101-150 unhealthy 

for sensitive groups; 151-200 unhealthy; 200+ 

very unhealthy

Tuesday’s reading na

Wednesday’s forecast Good

Critical pollutant Particulate Matter

Example 3. Newspaper longer form 

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 109 resulting from an ozone 

concentration of 0.079 ppm. Elsewhere in 

Baltimore, the air quality index was 87 or 

Moderate. Since today’s air quality is 

expected to be much the same, sensitive 

groups should consider limiting prolonged 

or heavy outdoor exertion.

►

GOOD

MODERATE

UNHEALTHY for SENSITIVE 

GROUPS

UNHEALTHY

VERY UNHEALTHY

HAZARDOUS
4

TELEVISION

The following is a short script that could be used for a television evening news/weather report. The 

graphics used in the report could be much the same as the graphics used in newspaper reports. The 

weathercaster must use the descriptors and, if a color format is used, colors for the categories that 

are listed above.

Example 4. 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. Active adults and children 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 5. A short form for television (evening) 

“The air quality index today was 156, a red air quality day. The air stagnation caused a buildup of 

ozone to unhealthy levels.”

Example 6. Two long forms for television (evening)

“Air quality today was unhealthy due to ozone, with an index value of 156. 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...”

“Tomorrow will be a code red air quality day for Center City. The cold winter air, morning traffic, and 

wood smoke are expected to cause particle pollution to rise to unhealthy levels. People with heart or 

lung disease, older adults, and children should avoid strenuous activities.”

TELEPHONE

Recorded telephone messages can be used to give more up-to-date information on the air quality. For 

example, the following script has been used:

Example 7. A script for telephone

“As of 10:00 a.m., the air quality index is 45 which is a good or “green” air quality day. The 

responsible pollutant is ozone.”

INTERNET

Most State and local agencies report the AQI on their public Web sites. The data available on the 

Web site are typically up to the most recent hour. Links to these sites can be found in the “Where I 

Live” section of the AirNow Web site, at www.airnow.gov.

Example 8. A short form for a Web page
5

Air Quality Index for St. Louis, MO

Time of this report: 1:00PM AQI: 110 Code: Orange

Responsible pollutant: Ozone Category: Unhealthy for Sensitive Groups

Example 9. A long form for a Web page- ozone

Air Quality Index for Chicago, IL for August 2

 Report as of: 2:00PM AQI: 162 Responsible pollutant: Ozone

Code: Red Category: Unhealthy

Sensitive groups: Active children and adults, and people with lung disease, such as asthma, 

should reduce prolonged or heavy outdoor exertion.

Health effects: Greater likelihood of respiratory symptoms and breathing difficulty in 

sensitive groups, possible respiratory effects in the general population.

HEALTH 

ADVISORY

Children and adults who are active outdoors, and people with lung 

disease, such as asthma should avoid moderate exertion outdoors, 

everyone else (especially children) should limit prolonged or heavy 

outdoor exertion.

Air Quality in South Chicago - Gary, IL AQI: 122 (Unhealthy for Sensitive Groups)

Tomorrow’s air quality in Chicago is 

predicted to be:

Unhealthy for Sensitive 

Groups

Code: Orange
6

Example 10. A long form for a Web page- particulate matter

Anchorage, Alaska

Alaska Department of Environmental Conservation (DEC) Issues Statewide Air Quality

AdvisoryThe AQI levels have been steadily increasing from Moderate to Unhealthy. Dense smoke advisory 

has been issued by the National Weather Service for the Fairbanks area for today and tonight. Poor 

air quality conditions are expected to persist for the next several days as a high pressure system to 

the northeast drives easterly winds and smoke to the Fairbanks area.

Health Tip: Everyone should avoid any outdoor exertion; people with respiratory or heart disease, the 

elderly, and children should remain indoors. 

Source: Alaska Department of Environmental Conservation and United States Environmental 

Protection Agency. 
7

What colors do I use in my AQI report?

If you report the Air Quality Index in a color format, the appropriate colors are specified in Appendix G 

as the following:

For this category ... ... use this color

Good Green

Moderate Yellow

Unhealthy for Sensitive Groups Orange

Unhealthy Red

Very Unhealthy Purple

Hazardous Maroon

Specific colors are defined in the table below for red, green, blue (RGB) and cyan, magenta, yellow, 

and black (CMYK) color formulas:

Color R G B C M Y K

Green 0 228 0 40 0 100 0

Yellow 255 255 0 0 0 100 0

Orange 255 126 0 0 52 100 0

Red 255 0 0 0 100 100 0

Purple 143 63 151 51 89 0 0

Maroon 126 0 35 30 100 100 30

Notes: The RGB model is traditionally used for screen colors, while CMYK is traditionally used for printing 

processes. The color models are based on a 0 - 255 scale (e.g. 50% is 126).

What health effects and cautionary statements should I use in my report?

The most recent health effect information used with the AQI is pollutant-specific. The following table 

lists the different health effects messages, sensitive groups, and cautionary statements for each 

pollutant in the AQI.
8

Pollutant-Specific Sub-indices and Health Effects Statements

for Guidance on the Air Quality Index (AQI)

AQI 

Categories:

Index Values

Ozone (ppm) Particulate Matter (μg/m3) Carbon Monoxide (ppm)

[8-hour]

Sulfur Dioxide

(ppb)

[1-hour]

Nitrogen Dioxide

(ppb)

[1-hour] [8-hour] [1-hour] PM

2.5 [24-hour] PM10 [24-hour]

Good

(Up to 50)

0 - 0.059

None

- 0 – 12.0

None

0 – 54

None

0 – 4.4

None

0 - 35

None

0 - 53

None

Moderate

(51 - 100)

0.060 - 0.075

Unusually sensitive 

individuals may 

experience respiratory 

symptoms.

- 12.1 – 35.4 55 – 154 4.4 – 9.4

None

36 - 75

None

54 - 100

None

Respiratory symptoms possible in unusually 

sensitive individuals, possible aggravation of heart 

or lung disease in people with cardiopulmonary 

disease and older adults.

Unhealthy for 

Sensitive Groups

(101 - 150)

0.076 - 0.095 0.125 - 0.164 35.5 – 55.4 155 – 254 9.5 – 12.4

Increasing likelihood of 

reduced exercise 

tolerance due to increased 

cardiovascular symptoms, 

such as chest pain, in 

people with heart disease.

76 - 185

Increasing likelihood of 

respiratory symptoms, 

such as chest tightness 

and breathing discomfort, 

in people with asthma.

101 - 360

Increasing likelihood of 

respiratory symptoms, 

such as chest tightness 

and breathing discomfort, 

in people with asthma.

Increasing likelihood of respiratory symptoms 

and breathing discomfort in people with lung 

disease, such as asthma, children, older adults 

and outdoor workers.

Increasing likelihood of respiratory symptoms in 

sensitive individuals, aggravation of heart or lung 

disease and premature mortality in people with 

cardiopulmonary disease, older adults, and people 

of lower SES.

Unhealthy

(151 - 200)

0.096 - 0.115 0.165 - 0.204 55.5 – 150.4 254 – 354 12.5 – 15.4

Reduced exercise 

tolerance due to increased 

cardiovascular symptoms, 

such as chest pain, in 

people with heart disease.

186 - 304

Increased respiratory 

symptoms, such as chest 

tightness and wheezing in 

people with asthma; 

possible aggravation of 

other lung diseases.

361 - 649

Increased respiratory 

symptoms, such as chest 

tightness and wheezing in 

people with asthma; 

possible aggravation of 

other lung diseases.

Greater likelihood of respiratory symptoms and 

breathing difficulty in people with lung disease, 

such as asthma, children, older adults, and 

outdoor workers; possible respiratory effects in 

general population.

Increased aggravation of heart or lung disease and 

premature mortality in people with cardiopulmonary 

disease, older adults, and people of lower SES; 

increased respiratory effects in general population.
9

Very Unhealthy

(201 - 300)

0.116 - 0.374 0.205 - 0.404 150.5 – 250.4 355 – 424 15.5 – 30.4

Significant aggravation of 

cardiovascular symptoms, 

such as chest pain, in 

people with heart disease.

305 – 604 [24-hour]

Significant increase in 

respiratory symptoms, 

such as wheezing and 

shortness of breath, in 

people with asthma; 

aggravation of other lung 

diseases.

650 - 1249

Significant increase in 

respiratory symptoms, 

such as wheezing and 

shortness of breath, in 

people with asthma; 

aggravation of other lung 

diseases.

Increasingly severe symptoms and impaired 

breathing likely in people with lung disease, 

such as asthma, children, older adults, and 

outdoor workers; increasing likelihood of 

respiratory effects in general population.

Significant aggravation of heart or lung disease and 

premature mortality in people with cardiopulmonary 

disease, older adults, and people of lower SES; 

significant increase in respiratory effects in general 

population.

Hazardous

(301 - 500)

- 0.405 - 0.604 250.5 – 500.4 425 – 604 30.5 – 50.4

Serious aggravation of 

cardiovascular symptoms, 

such as chest pain, in 

people with heart disease; 

impairment of strenuous 

activities in general 

population.

605 – 1004 [24-hour]

Severe respiratory 

symptoms, such as 

wheezing and shortness of 

breath, in people with 

asthma; increased 

aggravation of other lung 

diseases; possible 

respiratory effects in 

general population.

1249 - 2049

Severe respiratory 

symptoms, such as 

wheezing and shortness of 

breath, in people with 

asthma; increased 

aggravation of other lung 

diseases; possible 

respiratory effects in 

general population.

Severe respiratory effects and impaired 

breathing likely in people with lung disease, 

such as asthma, children, older adults and 

outdoor workers; increasingly severe 

respiratory effects likely in general population.

Serious aggravation of heart or lung disease and 

premature mortality in people with cardiopulmonary 

disease, older adults, and people of lower SES; 

serious risk of respiratory effects in general 

population.
10

Pollutant-Specific Sub-indices and Cautionary Statements

for Guidance on the Air Quality Index (AQI)

AQI 

Categories

(Index 

Values)

Ozone (ppm) Particulate Matter (μg/m3) Carbon Monoxide 

(ppm)

[8-hour]

Sulfur Dioxide

(ppb)

[1-hour]

Nitrogen Dioxide

(ppb)

[1-hour] [8-hour] [1-hour] PM

2.5 [24-hour] PM10 [24-hour]

Good

(Up to 50)

0 - 0.059

None

0 – 12.0

None

0 - 54

None

0 – 4.4

None

0 - 35

None

0 - 53

None

Moderate

(51 - 100)

0.060 - 0.075 12.1 – 35.4 55 – 154 4.5 – 9.4

None

36 - 75

None

54 - 100

Unusually sensitive 

individuals should 

consider limiting 

prolonged exertion 

especially near busy 

roads.

Unusually sensitive 

people should 

consider reducing 

prolonged or heavy 

outdoor exertion.

Unusually sensitive people should consider 

reducing prolonged or heavy exertion.

Unhealthy for 

Sensitive Groups

(101 - 150)

0.076 - 0.095 0.125 - 0.164 35.5 – 55.4 155 – 254 9.5 – 12.4

People with heart disease, 

such as angina, should 

limit heavy exertion and 

avoid sources of CO, such 

as heavy traffic.

76 - 185

People with asthma 

should consider limiting 

outdoor exertion.

101 - 360

People with asthma, 

children and older adults 

should limit prolonged 

exertion especially near 

busy roads.

People with lung disease, such as asthma, 

children, older adults, and outdoor workers 

should reduce prolonged or heavy outdoor 

exertion.

People with heart or lung disease, older adults, 

children, and people of lower SES should reduce 

prolonged or heavy exertion.
11

Unhealthy

(151 - 200)

0.096 - 0.115 0.165 - 0.204 55.5 – 150.4 255 – 354 12.5 – 15.4 186 – 304 361 - 649

People with lung disease, such as asthma, 

children, older adults, and outdoor workers 

should avoid prolonged or heavy outdoor 

exertion; everyone else should reduce 

prolonged or heavy outdoor exertion.

People with heart or lung disease, older adults, 

children, and people of lower SES should avoid 

prolonged or heavy exertion; everyone else should 

reduce prolonged or heavy exertion.

People with heart disease, 

such as angina, should 

limit moderate exertion 

and avoid sources of CO, 

such as heavy traffic.

Children, people with 

asthma, or other lung 

diseases, should limit 

outdoor exertion.

People with asthma, 

children and older adults 

should avoid prolonged 

exertion near roadways; 

everyone else should 

limit prolonged exertion 

especially near busy 

roads.

Very Unhealthy

(201 - 300)

0.116 - 0.374 0.205 - 0.404 150.5 – 250.4 355 – 424 15.5 – 30.4

People with heart disease, 

such as angina, should 

avoid exertion and 

sources of CO, such as 

heavy traffic.

305 – 604 [24-hour]

Children, people with 

asthma, or other lung 

diseases should avoid 

outdoor exertion; everyone 

else should reduce 

outdoor exertion.

650 - 1249

People with asthma, 

children and older adults 

should avoid all outdoor

exertion; everyone else 

should avoid prolonged 

exertion especially near 

busy roads.

People with lung disease, such as asthma, 

children, older adults, and outdoor workers 

should avoid all outdoor exertion; everyone 

else should reduce outdoor exertion.

People with heart or lung disease, older adults, 

children, and people of lower SES should avoid all 

physical activity outdoors. Everyone else should 

avoid prolonged or heavy exertion.

Hazardous

(301 - 500)

- 0.405 - 0.604 250.5 – 500.4 425 – 604 30.5 – 50.4

People with heart disease, 

such as angina, should 

avoid exertion and 

sources of CO, such as 

heavy traffic; everyone 

else should limit heavy 

exertion.

604 – 1004 [24-hour]

Children, people with 

asthma, or other lung 

diseases, should remain 

indoors; everyone else 

should avoid outdoor 

exertion.

1250 - 2049

People with asthma, 

children and older adults 

should remain indoors; 

everyone else should 

avoid all outdoor 

exertion.

Everyone should avoid all outdoor exertion. Everyone should avoid all physical activity outdoors; 

people with heart or lung disease, older adults, 

children, and people of lower SES should remain 

indoors and keep activity levels low.
12

Classifications and cautionary statements in Spanish: 

Use estas tarjetas para entender los efectos de la contaminación del aire cuando escuche las noticias 

del Indice de la Calidad del Aire.

Valores del 

Índice Clasificación Precauciones para Protegerse del Ozono

0 a 50 Buena Ninguna.

51 a 100 Moderada

Las personas extraordinariamente sensitivas deben 

considerar limitar los esfuerzos prolongados al aire 

libre.

101 a 150 Dañina a la Salud de 

los Grupos 

Sensitivos

Los niños y adultos activos, y las personas con 

enfermedades respiratorias, tales como el asthma, 

deben limitar los esfuerzos prolongados al aire libre.

151 a 200 Dañina a la Salud

Los niños y adultos activos, y las personas con 

enfermedades respiratorias, tales como el asthma, 

deben evitar el esfuerzo prolongado al aire libre; todos 

los demás, especialmente los niños, deben limitar el 

esfuerzo prolongado al aire libre.

201 a 300 Muy Dañina a la 

Salud

Los niños y adultos activos, y las personas con 

enfermedades respiratorias tales como el asthma, 

deben evitar cualquier esfuerzo al aire libre; todos los 

demás, especialmente los niños, deben limitar los 

esfuerzos al aire libre.

Se ha asignado un color específico a cada categoría de AQI. Por ejemplo, el rojo significa 

condiciones “dañinas a la salud” y el púrpura significa condiciones “muy dañinas a la salud”. Este 

esquema de colores puede ayudarle a determinar rápidamente si los contaminantes del aire están 

alcanzando niveles muy dañinos a la salud en su zona. 
13

How do I calculate the AQI from pollutant concentration data?

The AQI is the highest value calculated for each pollutant as follows: 

a. Identify the highest concentration among all of the monitors within each reporting area and truncate 

as follows:

Ozone – truncate to 3 decimal places

PM2.5 – truncate to 1 decimal place

PM10 – truncate to integer

CO – truncate to 1 decimal place

SO2 – truncate to integer

NO2 – truncate to integer

b. Using Table 2, find the two breakpoints that contain the concentration.

c. Using Equation 1, calculate the index.

d. Round the index to the nearest integer.

Equation 1:

I I I

BP BP (C BP ) I . p

Hi Lo

HI Lo

=

p Lo Lo

−

− − +

Where Ip = the index for pollutant p

Cp = the rounded concentration of pollutant p

BPHi = the breakpoint that is greater than or equal to Cp

BPLo = the breakpoint that is less than or equal to Cp

 BPHi = the breakpoint that is greater than or equal to Cp

IHi = the AQI value corresponding to BPHi

ILo = the AQI value corresponding to BPLo
14

Table 2: Breakpoints for the AQI

These Breakpoints... ...equal 

this AQI

...and this 

category

O3

(ppm)

8-hour

O3

(ppm)

1-hour1

PM10

(μg/m3)

24-hour

PM2.5

(μg/m3

)

24-hour

CO

(ppm)

8-hour

SO2

(ppb)

1-hour

NO2

(ppb)

1-hour

AQI

0.000 -

0.059

- 0 - 54 0.0 –

12.0

0.0 - 4.4 0 - 35 0 - 53 0 - 50 Good

0.060 -

0.075

- 55 - 154 12.1 -

35.4

4.5 - 9.4 36 - 75 54 - 100 51 - 100 Moderate

0.076 -

0.095

0.125 -

0.164

155 -

254

35.5 -

55.4

9.5 -

12.4

76 - 185 101 -

360

101 - 150 Unhealthy for 

Sensitive Groups

0.096 -

0.115

0.165 -

0.204

255 -

354

(55.5 -

150.4)

3

12.5 -

15.4

(186 -

304)

4

361 -

649

151 - 200 Unhealthy

0.116 -

0.374

0.205 -

0.404

355 -

424

(150.5 -

(250.4)

3

15.5 -

30.4

(305 -

604)

4

650 -

1249

201 - 300 Very unhealthy

(

2

) 0.405 -

0.504

425 -

504

(250.5 -

(350.4)

3

30.5 -

40.4

(605 -

804)

4

1250 -

1649

301 - 400 Hazardous

(

2

) 0.505 -

0.604

505 -

604

(350.5 -

500.4)

3

40.5 -

50.4

(805 -

1004)

4

1650 -

2049

401 - 500 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 value may be calculated, and the 

maximum of the two values reported.

2 8-hour O3 values do not define higher AQI values (≥ 301). AQI values of 301 or higher are calculated with 1-

hour O3 concentrations.

3 If a different SHL for PM2.5 is promulgated, these numbers will change accordingly.

4 1-hour SO2 values do not define higher AQI values (≥ 200). AQI values of 200 or greater are calculated with 

24-hour SO2 concentrations.
15

How do I use the table and the equation and my concentration data to calculate the AQI?

Suppose you have an 8-hour ozone value of 0.08753333. First, round off the value to 0.087. Then 

refer to the 8-hour ozone in table 2 for the values that fall above and below your value (0.076-0.095). 

In this case, the 0.087 value falls within the index values of 101 to 150. Now you have all the 

numbers needed to use the equation.

So an 8-hour value of 0.08753333 corresponds to an index value of 129.

What if I have values for more pollutants?

Suppose you have an 8-hour ozone value of 0.077 ppm, a PM2.5 value of 35.9 μg/m3

, and a CO value 

of 8.4 ppm. You apply the equation 3-times:

The AQI is 104, with ozone as the responsible pollutant.

How do I use both ozone 1-hour and 8-hour values?

You must calculate the 8-hour values, and you may also calculate the 1-hour values. If you calculate 

both, you must report the higher AQI value.

Suppose you had a 1-hour value of 0.162ppm and an 8-hour value of 0.141 ppm. Then you apply the 

equation twice:

In this case, the index is 211 (the maximum of 204 and 211) and the responsible pollutant is ozone.

1 300 201

404 155 162 155 201 204

8 300 201

374 116

141 116 201 211

− −

− − + =

− −

− − + =

hr

hr

:

( )

(. . )

(. . )

:

( )

(. . )

(. . )

O

PM

CO

3

150 101

095 076

077 076 101 104

150 101

55 4 35 5

35.9 35 5 101 =102

100 51

9 4 4 5

8 4 4 5 51 90

:

( )

(. . )

(. . )

:

( )

( . . )

( . )

:

( )

( . . )

( . . )

−

− − + =

−

− − +

−

− − + =

( )

(. . )

(. . ) . . 150 101

095 076

087 076 101

49

019

011 101 129.368 129 −

− − + = + = =
16

How do I calculate AQI values for SO2?

EPA strengthened the primary standard for SO2 in 2010. Because there was not enough health 

information to inform changing the upper end of the AQI for SO2, the upper end continues to use the 

24-hour average SO2 concentration. The lower end of the AQI uses the new daily max 1-hour SO2 

concentration.

If you have a daily max 1-hour SO2 concentration below 305 ppb, then use the breakpoints in Table 2 

to calculate the AQI value. 

If you have a 24-hour average SO2 concentration greater than or equal to 305 ppb, then use the 

breakpoints in Table 2 to calculate the AQI value. If you have a 24-hour value in this range, it will 

always result in a higher AQI value than a 1-hour value would. 

On rare occasions, you could have a day where the daily max 1-hour concentration is at or above 305 

ppb but when you try to use the 24-hour average to calculate the AQI value, you find that the 24-hour 

concentration is not above 305 ppb. If this happens, use 200 for the lower and upper AQI breakpoints 

(ILo and IHi) in Equation 1 to calculate the AQI value based on the daily max 1-hour value. This 

effectively fixes the AQI value at 200 exactly, which ensures that you get the highest possible AQI 

value associated with your 1-hour concentration on such days.

What do I do with concentrations for pollutants that have blank places in the table for 

Breakpoints for the AQI?

Disregard those numbers. Suppose you had a 1-hour ozone value of 0.104ppm and an 8-hour ozone 

value of 0.087ppm. First you disregard the 1-hour ozone value because it is less than 0.125ppm. 

Then you calculate the index for the 8-hour ozone value as before:

This value rounds to 129.

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 an extended period of time (for 

example, for that particular season), then you are not required to include this pollutant in the 

calculation of the AQI.

The final rule allows agencies to discontinue reporting for any pollutant if index values for that 

pollutant have been below 50 for an entire season or a year. However, this does not hold if in 

subsequent years’ pollutant levels rise so that index values for that pollutant would be above 50 and 

the criteria for an exemption are no longer met. In these cases, section 8 of appendix G now requires 

that the responsible agency must again report the AQI. 

( )

(. . )

(. . )

150 101

095 076

087 076 101 129.368 −

− − + =
17

Do I have to forecast pollutant concentrations for the AQI report?

Although not required, you are encouraged to forecast values at least 24 hours in advance. The AQI 

is designed to inform members of sensitive groups and the general population so that they may 

choose to reduce or avoid exposure to certain levels and types of air pollution. If the information is 

not timely, the public cannot make this choice. However, good forecasts may 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 AQI reporting in your Metropolitan Statistical 

Area (MSA).

Since ozone is a dominant pollutant in AQI reporting and the form of the ozone standard is an 8-hour 

average, the timing of how the public is informed is an important issue, even if you have decided not 

to forecast 24 hours in advance. In order for potentially affected people 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; the 

method you can use relies on the high correlation between daily maximum of 8-hour ozone and 1-

hour ozone values. A simple linear regression can be calculated on daily max data at any site. From 

this regression, you can predict that the 8-hour ozone maximum for a day will be at least the 

corresponding maximum 8-hour value, given the present 1-hour value. From this information, you can 

estimate the AQI without having to wait for the full 8-hour maximum to be observed.

What if the correlation at my site is low- can I still forecast the AQI?

The lowest observed correlation at any site reporting to AIRS data was 0.86, which is adequate to 

predict the maximum 8-hour values from the maximum 1-hour for reporting the AQI. However, if you 

feel uncomfortable from either a public health or cost viewpoint, you may want to use a confidence 

interval for the decision you make based on the predicted 8-hour maximum. For example, if your 

ozone action day is declared when you reach the unhealthy category and you predict an unhealthy 

day but are unsure whether or not you should call an “ozone action day” based on this prediction, you 

can use the confidence interval of the predicted value to trigger your decision. If you are concerned 

about public health, you might consider calling an “ozone action day” as soon as the upper bound of 

the confidence interval is greater than the AQI cut-point for the unhealthy category. If you are 

concerned with the cost of calling an “ozone action day” unnecessarily, then you might consider 

calling an ozone action day only when the lower bound of the confidence interval is above the cutpoint for the unhealthy category.

Is there anything else I should know about reporting the AQI?

For further information, go to www.epa.gov/airnow. Under “Publications,” there are several 

informative documents to help you report the AQI, including the ones listed:

• AQI brochure

• AQI calculator program

• Forecasting guidance

• Air quality guides for: 

-Ozone

-Particle pollution

• Pamphlets:

-Ozone Pollution and your Health

-Particle Pollution and your Health

-Smog: Who does it Hurt?

• Medical poster

• Ozone web course for health care 

providers
18

How do I calculate the upper and lower bounds of 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 Se

2

. Then you calculate the upper and lower 

bounds of the predicted value as:

Where:



Y is the predicted 8-hour ozone maximum,

t1-α/2,n-2 is a tabulated Student’s-T value corresponding to a two sided (1- α)100% confidence 

interval with n-2 degrees of freedom,

Se

2 is the error variance described above,

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

x is the average of the 1-hour values, and

Sx

2 is the variance of the 1-hour values.

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

interval.

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 2 2

2

2

2

1 2 2

2

2

2

1

1

1

1

1

1

α

α
19

APPENDIX
20

Table 3: Metropolitan Statistical Areas with over 350,000 population (2010 Census)

CBSA code Geographic Area 2010 Census

10420 Akron, OH 703,200

10580 Albany-Schenectady-Troy, NY 870,716

10740 Albuquerque, NM 887,077

10900 Allentown-Bethlehem-Easton, PA-NJ 821,173

11260 Anchorage, AK 380,821

11700 Asheville, NC 424,858

12060 Atlanta-Sandy Springs-Marietta, GA 5,268,860

12260 Augusta-Richmond County, GA-SC 556,877

12420 Austin-Round Rock-San Marcos, TX 1,716,289

12540 Bakersfield-Delano, CA 839,631

12580 Baltimore-Towson, MD 2,710,489

12940 Baton Rouge, LA 802,484

13140 Beaumont-Port Arthur, TX 388,745

13820 Birmingham-Hoover, AL 1,128,047

14260 Boise City-Nampa, ID 616,561

14460 Boston-Cambridge-Quincy, MA-NH 4,552,402

14860 Bridgeport-Stamford-Norwalk, CT 916,829

15180 Brownsville-Harlingen, TX 406,220

15380 Buffalo-Niagara Falls, NY 1,135,509

15940 Canton-Massillon, OH 404,422

15980 Cape Coral-Fort Myers, FL 618,754

16700 Charleston-North Charleston-Summerville, SC 664,607

16740 Charlotte-Gastonia-Rock Hill, NC-SC 1,758,038

16860 Chattanooga, TN-GA 528,143

16980 Chicago-Joliet-Naperville, IL-IN-WI 9,461,105

17140 Cincinnati-Middletown, OH-KY-IN 2,130,151

17460 Cleveland-Elyria-Mentor, OH 2,077,240

17820 Colorado Springs, CO 645,613

17900 Columbia, SC 767,598

18140 Columbus, OH 1,836,536

18580 Corpus Christi, TX 428,185

19100 Dallas-Fort Worth-Arlington, TX 6,371,773

19340 Davenport-Moline-Rock Island, IA-IL 379,690

19380 Dayton, OH 841,502

19660 Deltona-Daytona Beach-Ormond Beach, FL 494,593

19740 Denver-Aurora-Broomfield, CO 2,543,482

19780 Des Moines-West Des Moines, IA 569,633

19820 Detroit-Warren-Livonia, MI 4,296,250

20500 Durham-Chapel Hill, NC 504,357

21340 El Paso, TX 800,647

21660 Eugene-Springfield, OR 351,715

21780 Evansville, IN-KY 358,676

22180 Fayetteville, NC 366,383

22220 Fayetteville-Springdale-Rogers, AR-MO 463,204

22420 Flint, MI 425,790

23060 Fort Wayne, IN 416,257

23420 Fresno, CA 930,450

24340 Grand Rapids-Wyoming, MI 774,160
21

24660 Greensboro-High Point, NC 723,801

24860 Greenville-Mauldin-Easley, SC 636,986

25420 Harrisburg-Carlisle, PA 549,475

25540 Hartford-West Hartford-East Hartford, CT 1,212,381

25860 Hickory-Lenoir-Morganton, NC 365,497

26180 Honolulu, HI 953,207

26420 Houston-Sugar Land-Baytown, TX 5,946,800

26620 Huntsville, AL 417,593

26900 Indianapolis-Carmel, IN 1,756,241

27140 Jackson, MS 539,057

27260 Jacksonville, FL 1,345,596

28140 Kansas City, MO-KS 2,035,334

28660 Killeen-Temple-Fort Hood, TX 405,300

28940 Knoxville, TN 698,030

29460 Lakeland-Winter Haven, FL 602,095

29540 Lancaster, PA 519,445

29620 Lansing-East Lansing, MI 464,036

29820 Las Vegas-Paradise, NV 1,951,269

30460 Lexington-Fayette, KY 472,099

30780 Little Rock-North Little Rock-Conway, AR 699,757

31100 Los Angeles-Long Beach-Santa Ana, CA 12,828,837

31140 Louisville/Jefferson County, KY-IN 1,283,566

31540 Madison, WI 568,593

31700 Manchester-Nashua, NH 400,721

32580 McAllen-Edinburg-Mission, TX 774,769

32820 Memphis, TN-MS-AR 1,316,100

33100 Miami-Fort Lauderdale-Pompano Beach, FL 5,564,635

33340 Milwaukee-Waukesha-West Allis, WI 1,555,908

33460 Minneapolis-St. Paul-Bloomington, MN-WI 3,279,833

33660 Mobile, AL 412,992

33700 Modesto, CA 514,453

33860 Montgomery, AL 374,536

34980 Nashville-Davidson--Murfreesboro--Franklin, TN 1,589,934

35300 New Haven-Milford, CT 862,477

35380 New Orleans-Metairie-Kenner, LA 1,167,764

35620

New York-Northern New Jersey-Long Island, NY-NJ-

PA 18,897,109

35840 North Port-Bradenton-Sarasota, FL702,281

36260 Ogden-Clearfield, UT 547,184

36420 Oklahoma City, OK 1,252,987

36540 Omaha-Council Bluffs, NE-IA 865,350

36740 Orlando-Kissimmee-Sanford, FL 2,134,411

37100 Oxnard-Thousand Oaks-Ventura, CA 823,318

37340 Palm Bay-Melbourne-Titusville, FL 543,376

37860 Pensacola-Ferry Pass-Brent, FL 448,991

37900 Peoria, IL 379,186

37980 Philadelphia-Camden-Wilmington, PA-NJ-DE-MD 5,965,343

38060 Phoenix-Mesa-Glendale, AZ 4,192,887

38300 Pittsburgh, PA 2,356,285

38860 Portland-South Portland-Biddeford, ME 514,098

38900 Portland-Vancouver-Hillsboro, OR-WA 2,226,009
22

38940 Port St. Lucie, FL 424,107

39100 Poughkeepsie-Newburgh-Middletown, NY 670,301

39300 Providence-New Bedford-Fall River, RI-MA 1,600,852

39340 Provo-Orem, UT 526,810

39580 Raleigh-Cary, NC 1,130,490

39740 Reading, PA 411,442

39900 Reno-Sparks, NV 425,417

40060 Richmond, VA 1,258,251

40140 Riverside-San Bernardino-Ontario, CA 4,224,851

40380 Rochester, NY 1,054,323

40900 Sacramento--Arden-Arcade--Roseville, CA 2,149,127

41180 St. Louis, MO-IL 2,812,896

41420 Salem, OR 390,738

41500 Salinas, CA 415,057

41620 Salt Lake City, UT 1,124,197

41700 San Antonio-New Braunfels, TX 2,142,508

41740 San Diego-Carlsbad-San Marcos, CA 3,095,313

41860 San Francisco-Oakland-Fremont, CA 4,335,391

41940 San Jose-Sunnyvale-Santa Clara, CA 1,836,911

42060 Santa Barbara-Santa Maria-Goleta, CA 423,895

42220 Santa Rosa-Petaluma, CA 483,878

42340 Savannah, GA 347,611

42540 Scranton--Wilkes-Barre, PA 563,631

42660 Seattle-Tacoma-Bellevue, WA 3,439,809

43340 Shreveport-Bossier City, LA 398,604

44060 Spokane, WA 471,221

44140 Springfield, MA 692,942

44180 Springfield, MO 436,712

44700 Stockton, CA 685,306

45060 Syracuse, NY 662,577

45220 Tallahassee, FL 367,413

45300 Tampa-St. Petersburg-Clearwater, FL 2,783,243

45780 Toledo, OH 651,429

45940 Trenton-Ewing, NJ 366,513

46060 Tucson, AZ 980,263

46140 Tulsa, OK 937,478

46700 Vallejo-Fairfield, CA 413,344

47260 Virginia Beach-Norfolk-Newport News, VA-NC 1,671,683

47300 Visalia-Porterville, CA 442,179

47900 Washington-Arlington-Alexandria, DC-VA-MD-WV 5,582,170

48620 Wichita, KS 623,061

48900 Wilmington, NC 362,315

49180 Winston-Salem, NC 477,717

49340 Worcester, MA 798,552

49620 York-Hanover, PA 434,972

49660 Youngstown-Warren-Boardman, OH-PA 565,773

Source: U.S. Census Bureau, Population Division, Annual Estimates of the Population of Metropolitan and 

Micropolitan Statistical Areas: April 1, 2010 to July 1, 2011 (CBSA-EST2011-01), Release Date: April 2012, 

http://www.census.gov/popest/data/metro/totals/2011/
23

FREQUENTLY ASKED QUESTIONS

I want to buy an air purifier. Are the purifiers that produce ozone helpful to my indoor air 

quality? 

Some air cleaning devices, such as ozone generators and ionic air purifiers, can generate significant 

levels of ozone. Even at low levels, ozone triggers a variety of health problems, including aggravated 

asthma and increased susceptibility to respiratory illnesses. Additional information on the assessment 

of the effectiveness and health consequences of ozone generators that are sold as air cleaners can 

be found at http://www.epa.gov/iaq/pubs/ozonegen.html, and also at the California Air Resources 

Board Web site at http://www.arb.ca.gov/research/indoor/ozone_gen_fact_sheet-a.pdf.

If you’re having issues with mold and moisture, solutions and preventative tips are offered at 

http://www.epa.gov/mold/index.html. For additional questions about indoor air quality, please use 

the EPA Office of Indoor Air Quality hotline at 1-800-438-4318.

Why is my area not covered in the Air Quality Index?

Towns and cities with 350,000 or fewer inhabitants are not required to report the AQI. Also, AirNow is 

a voluntary program based upon state and local air quality monitoring networks. Some networks don't 

submit their data, or don’t have any monitors in the area. 

The other day, the air quality in my area was reported as green, or good air quality. However, 

it was pretty hazy outside. Why didn’t the AQI report this accurately?

There are a couple of reasons why this may have occurred, depending on what was “reported.” If this 

was an AQI forecast, there are still some parts of the United States that only forecast for ozone and 

not particle pollution. It is possible that the forecast ozone AQI was “GOOD” and the hazy conditions 

experienced were due to particle pollution. In this instance, the “reported” AQI forecast may have only 

represented ozone. As more and more areas begin forecasting for PM2.5 and ozone together, this 

discrepancy should diminish.

In the case of real-time data, the AirNow program provides separate maps for ozone and PM2.5 AQI. 

It is possible that the ozone AQI maps were showing “GOOD” conditions and the PM2.5 maps 

showing “MODERATE” or above conditions. It is important to check both maps for a specific 

geographical area to cover both primary pollutants. In the future, AirNow plans to have combined AQI 

maps of both ozone and PM2.5 that will eliminate this problem, but will continue to provide the 

separate pollutant AQI maps to allow for people to identify the pollutant of concern.

Finally, it should be noted that there are occasions where hazy conditions may be due primarily to 

high humidity and not pollution. On these days, it is still good to check the AQI maps and forecasts to 

make sure that pollution is not the primary cause of the haze.

How do I get my newspaper to publish the AQI? 

Most newspaper weather pages and graphics are developed and produced by private weather service 

providers. We recommend that you direct your initial approach to the newspaper editors, since they 

are the customers of the weather provider company. In general, newspapers want to provide more 

health-based information to their readers. However, it may take some effort to educate decision

makers about the importance of providing air quality information to the public. When you meet with 

the newspaper staff, bring along this guidance document or several examples showing how other 
24

newspapers publish the AQI. In addition, most weather service providers already have access to the 

air quality data through AirNow, which makes it easier for them to acquire and publish the information. 

Space on weather pages is limited, so a small, compact graphic might be a better choice for a 

crowded weather page. 

If the AQI reported in the newspaper is incorrect, what should I do?

Common problems with AQI reporting in newspapers include either reporting data values that are 

wrong or reporting pollutant concentrations instead of the AQI. Another frequent mistake is to report 

inconsistent AQI colors or terminology, as well as incorrect pollutant names. Establishing a good 

working relationship with the newspaper and educating them about how misleading or erroneous AQI 

information can impact their readers could help minimize potential problems. We recommend that 

you first notify the newspaper directly about any error so they can relay discrepancies to their weather 

service provider as a paying customer. If you have difficulty getting the newspaper to correct the 

issue, you could team with other health and nongovernmental organizations to approach the 

newspaper editor with a united message and request.

Should I report yesterday’s observed value, today’s forecast, or tomorrow’s forecast to the 

newspaper?

Let's assume that today is Monday, and you are submitting data for Tuesday morning's paper. Let's 

also assume that the paper is willing to carry both the observed AQI and the forecast. In such a case:

• Send the paper the most recent observed AQI. If it's midnight to midnight, that means

Sunday's data.

• Send the Tuesday forecast so there is a "day-of" forecast in the Tuesday paper.

• If you have the Wednesday forecast and they're willing to carry that, include it too.

My local newspaper has a deadline of 2 pm for the next day’s paper. Should I report the AQI 

value through 1 pm, or report the forecast?

Again, since the true AQI is a midnight to midnight calculation, we recommend that you report 

tomorrow's forecast. If this is not possible, then report the AQI value through a certain time, but make 

sure the newspaper includes the reporting period to avoid confusion.

How do I get my local TV station to show the AQI?

Similar to the newspaper industry, television reporting reflects the culture of the local community and 

what competing stations show. Television stations use weather service providers to provide graphics 

and data support for their weathercasts. All of the weather service companies have access to the air 

quality data through AirNow, which makes it easy for them to acquire and provide these data to their 

television station customers. There are several questions that need to be addressed: Does the 

station want to show air quality information? Do other stations in your market show air quality 

information? Is the station news director on board with providing this information? Does the station 

have the proper software to access the air quality data? 

For stations that have never shown these data on the air, you will need to establish a relationship and 

educate them about the benefits of providing air quality information to their viewers. Air quality is 

weather, news and health all in one. Once a station in your market begins to provide air quality 

information, chances are good that other stations will follow suit. However, even if the weathercasters 

want to provide this information in their weathercasts, the station news director controls the content of 
25

what goes on the air. In addition, if the station wants to show the AQI on the air, they need to have 

the proper software version of weather graphics products to access and display the AQI. Keep in 

mind that air quality information could be displayed only during periods of high pollution levels, when it 

is considered more "newsworthy."

Can we still use the Pollutant Standards Index?

No. The Air Quality Index is required by law.

Does providing our data and forecasts to AirNow meet the AQI reporting requirements?

No. Even though the air quality information that you provide to AirNow is distributed on a national 

basis to the media and weather service provider companies, there is no guarantee that this 

information ends up within the media (newspaper, radio, or web site) in your local community as 

required.

Why doesn't the AQI cover toxic air pollutants or air toxics?

While the AQI is an excellent indicator of the air quality resulting from ozone and particulate matter, it 

does not directly include health implications from air pollutants such as air toxics. Adverse health 

effects from air toxics are generally not believed to be episodic in nature like ozone and particulate 

matter, and are usually evaluated on a longer term, or chronic, basis. For information on 

concentrations of air toxics, refer to EPA’s National Air Toxics Assessment (NATA) Website at: 

http://www.epa.gov/ttn/atw/nata/.

Why does EPA issue AQI forecasts only for ozone and particle pollution?

AQI reporting is required for all criteria pollutants when they have an index value of 50 or above. Most 

cities forecast for ozone and particle pollution as these pollutants are the major sources of unhealthy 

air quality around 99% of the time. However, several cities forecast for all five pollutants- ground-level 

ozone, particle pollution, carbon monoxide, sulfur dioxide, and nitrogen dioxide.

Should I use particulate matter or particle pollution when speaking with the public?

Based on focus group testing by EPA, people better understand and prefer the term “particle 

pollution” than "particulate matter."
26

United States

Environmental Protection

Agency

Office of Air Quality Planning and 

Standards

Research Triangle Park, NC 27711

Publication No. EPA454/B-13-001

December 2013