Technical Assistance Document 

for the Reporting of Daily Air Quality – 

the Air Quality Index (AQI) 

 
EPA-454/B-09-001 

 February 2009 

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....................................................... 25 
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. The U.S. Office of Management and Budget 

defines MSAs according to the 2000 census. 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, 

 and children are the groups most at risk 

PM10 People with heart or lung disease, older 

adults, and children and the groups most at risk 

CO People with heart disease are the group most at risk 

 

SO2 People with asthma are the group 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. 

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: 76

Main pollutant: Particulate Matter 
3

 ▼

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 

GOOD

MODERATE

UNHEALTHY for SENSITIVE 

GROUPS

UNHEALTHY

VERY UNHEALTHY

HAZARDOUS

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. 

►

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. 
4

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

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
5

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
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. 

6
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 below2

 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 153 0 76 10 100 40 30

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.
Pollutant-Specific Sub-indices and Health Effects Statements 

for Guidance on the Air Quality Index (AQI)

Ozone (ppm) Particulate Matter (μg/m3 AQI )

Categories: 

Index Values [8-hour] [1-hour] PM2.5 [24-hour] PM10 [24-hour]

Carbon Monoxide 

(ppm) 

[8-hour]

Good (Up to 50)

0 - 0.059 

None

0 - 15 

None

0 - 50 

None

0 - 4 

None

Moderate 0.060 - 0.075 >15 - 40 >50 - 150(51 - 100)

Unusually sensitive individuals may experience respiratory symptoms.

Respiratory symptoms possible in unusually sensitive individuals, possible aggravation of heart or lung disease in people with cardiopulmonary disease and older adults.

>4 - 9 

None

Unhealthy for 0.076 - 0.095 0.125 - 0.164 >40 - 65 >150 - 250Sensitive Groups (101 - 150) Increasing likelihood of respiratory symptoms and 

breathing discomfort in active children and adults and people with lung disease, such as asthma.

Increasing likelihood of respiratory symptoms in sensitive individuals, aggravation of heart or lung disease and premature mortality in people with cardiopulmonary disease and older adults. 

>9 - 12 

Increasing likelihood of reduced exercise tolerance due to increased cardiovascular symptoms, such as chest pain, in people with heart disease.

Unhealthy 0.096 - 0.115 0.165 - 0.194 >65 - 150 >250 - 350(151 - 200)

Greater likelihood of respiratory symptoms and breathing difficulty in active children and adults and people with lung disease, such as asthma; possible respiratory effects in general population.

Increased aggravation of heart or lung disease and premature mortality in people with cardiopulmonary disease and older adults; increased respiratory effects in general population. 

>12 - 15 

Reduced exercise tolerance due to increased cardiovascular symptoms, such as chest pain, in people with heart disease.
Very Unhealthy 0.116 [8-hr] - 0.404 [1-hr] 0.195 - 0.404 >150 - 250 >350 - 420(201 - 300)

Increasingly severe symptoms and impaired breathing likely in active children and adults and people with lung disease, such as asthma; increasing likelihood of respiratory effects in general population.

Significant aggravation of heart or lung disease and premature mortality in people with cardiopulmonary disease and older adults; significant increase in respiratory effects in general population. 

>15 - 30 

Significant aggravation of cardiovascular symptoms, such as chest pain, in people with heart disease.

Hazardous 0.405 [1-hr] - 0.60 [1-hr] 0.405 - 0.60 >250 - 500 >420 - 600(301 - 500)

Severe respiratory effects and impaired breathing likely in active children and adults and people with lung disease, such as asthma; increasingly severe respiratory effects likely in general population.

Serious aggravation of heart or lung disease and premature mortality in people with cardiopulmonary disease and older adults; serious risk of respiratory effects in general population. 

>30 - 50 

Serious aggravation of cardiovascular symptoms, such as chest pain, in people with heart disease; impairment of strenuous activities in general population.
Pollutant-Specific Sub-indices and Cautionary Statements 

for Guidance on the Air Quality Index (AQI)

Ozone (ppm) Particulate Matter (μg/m3 AQI )

Categories 

(Index 

Values)

[8-hour] [1-hour] PM2.5 [24-hour] PM10 [24-hour]

Carbon Monoxide 

(ppm) 

[8-hour]

Good (Up to 50)

0 - 0.059 

None

0 - 15 

None

0 - 50 

None

0 - 4 

None

Moderate 0.060 - 0.075 >15 - 40 >50 - 150(51 - 100)

Unusually sensitive people should consider reducing prolonged or heavy outdoor exertion.

Unusually sensitive people should consider reducing prolonged or heavy exertion.

>4 - 9 

None

Unhealthy for 0.076 - 0.095 0.125 - 0.164 >40 - 65 >150 - 250Sensitive Groups (101 - 150)

Active children and adults, and people with lung disease, such as asthma, should reduce prolonged or heavy outdoor exertion. 

People with heart or lung disease, older adults, and children should reduce prolonged or heavy exertion.

>9 - 12 

People with heart disease, such as angina, should limit heavy exertion and avoid sources of CO, such as heavy traffic.
Unhealthy 0.096 - 0.115 0.165 - 0.194 >65 - 150 >250 - 350(151 - 200)

Active children and adults, and people with lung disease, such as asthma, should avoid prolonged or heavy outdoor exertion; everyone else, especially children, should reduce prolonged or heavy outdoor exertion.

People with heart or lung disease, older adults, and children should avoid prolonged or heavy exertion; everyone else should reduce prolonged or heavy exertion.

>12 - 15 

People with heart disease, such as angina, should limit moderate exertion and avoid sources of CO, such as heavy traffic.

Very Unhealthy 0.116 [8-hr] - 0.404 [1-hr] 0.195 - 0.404 >150 - 250 >350 - 420(201 - 300)

Active children and adults, and people with lung disease, such as asthma, should avoid all outdoor exertion; everyone else, especially children, should reduce outdoor exertion.

People with heart or lung disease, older adults, and children should avoid all physical activity outdoors. Everyone else should avoid prolonged or heavy exertion.

>15 - 30 

People with heart disease, such as angina, should avoid exertion and sources of CO, such as heavy traffic.

0.405 [1-hr] - 0.60 [1-hr] 0.405 - 0.60 >250 - 500 >420 - 600 Hazardous 

(301 - 500)

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

people with heart or lung disease, older adults, and children should remain indoors and keep activity levels low.

>30 - 50 

People with heart disease, such as angina, should avoid exertion and sources of CO, such as heavy traffic; everyone else should limit heavy exertion
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

DaΖina a la Salud de 

los Grupos 

Sensitivos

Los niΖos y adultos activos, y las personas con 

enfermedades respiratorias, tales como el asthma, 

deben limitar los esfuerzos prolongados al aire libre.

151 a 200 DaΖina a la Salud

Los niΖos 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 niΖos, deben limitar el 

esfuerzo prolongado al aire libre.

201 a 300 Muy DaΖina a la 

Salud

Los niΖos 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 niΖos, deben limitar los 

esfuerzos al aire libre.

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

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

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

alcanzando niveles muy daΖinos a la salud en su zona. 
How do I calculate the AQI from pollutant concentration data? 

 You calculate the AQI by using your pollutant concentration data, the following table, and the 

following equation (linear interpolation): 

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

13
14

Table 2: Breakpoints for the AQI 

This Breakpoint... ...equal this AQI ...and this 

category

o3 (ppm)

8-hour

O3 (ppm)

1-hour1

PM10

(μg/m3)

PM2.5

(μg/m3

)

CO 

(ppm)

SO2 (ppm) NO2

(ppm)

AQI

0.000 - 

0.059

 - 0 - 54 0.0 - 15.4 0.0 - 4.4 0.000 - 

0.034

(

2

) 0 - 50 Good

0.060 - 

0.075

- 55 - 

154

15.5 -40.4 4.5 - 9.4 0.035 - 

0.144

(

2

) 51 - 100 Moderate

0.076 - 

0.095

0.125 - 

0.164

155 - 

254

40.5 - 65.4 9.5 - 

12.4

0.145 -

0.224

(

2

) 101 - 150 Unhealthy for 

Sensitive Groups

0.096 - 

0.115

0.165 - 

0.204

255 - 

354

65.5 - 

150.4

12.5 - 

15.4

0.225 - 

0.304

(

2

) 151 - 200 Unhealthy

0.116 - 

0.374 

(0.155 - 

0.404)4

0.205 - 

0.404

355 - 

424

150.5 - 

250.4

15.5 - 

30.4

0.305 - 

0.604

0.65 - 

1.24

201 - 300 Very unhealthy

(

3

) 0.405 - 

0.504

425 - 

504

250.5 - 

350.4

30.5 - 

40.4

0.605 - 

0.804

1.25 - 

1.64

301 - 400 Hazardous

(

3

) 0.505 - 

0.604

505 - 

604

350.5 - 

500.4

40.5 - 

50.4

0.805 - 

1.004

1.65 - 

2.04

401 - 500 Hazardous

1

 Areas are required to report the AQI based on 8-hour ozone values. However, there are areas where an AQI 

based on 1-hour ozone values would be more protective. In these cases the index for both the 8-hour and the 

1-hour ozone values may be calculated and the maximum AQI reported. 

2

 NO2 has no short-term NAAQS and can generate an AQI only above a value of 200. 

3

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

hour O3 concentrations. 

4

 The numbers in parentheses are associated 1-hour values to be used in this overlapping category only. 
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. 

− + = −

49

101 .019 (.087 .076) (.095 .076)

(150 −101) .011 +101 = 129.368= 129

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 40.9 μg/m3

, and a CO value 

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

−

)

(8.4

9( 4. − 4 5.

1( 00 − 51 )

1( 50 101)

(40.9 

(65.4 − 40.5

−.0

(.095−.076

101)

(.077

)

(150 − O + = 104

3: 76) 101

PM: − 40.5) + 101 =102

CO: − 4 5. ) + 51 = 90

)

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: 

)

300 201

(.374 116

141 116 201 −

−. − + ( )

(. . ) )

(.162−.155 201 (.404−.155

(300 − 201) 1− hr: ) + = 204

8 − hr: = 211

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

15
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, an 8-hour ozone 

value of 0.087ppm and an NO2 value of 0.54ppm. First you disregard the 1-hour ozone value 

because it is less than 0.125ppm and the NO2 value because it is less than 0.65ppm. Then you 

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

(.095−.076)

(150 −101)

(.087−.076) +101 = 129.368

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. 

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. 

16
17

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 
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: 

upper Yt S

n

x x

n S

lower Yt 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

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. 

18
19

 

APPENDIX
20

Table 3: Metropolitan Statistical Areas with over 350,000 population (2000 Census)

MSA NAME STATE POPULATION

1000 Birmingham, AL MSA AL 921,106

5160 Mobile, AL MSA AL 540,258

4400 Little Rock--North Little Rock, AR MSA AR 583,845

6200 Phoenix--Mesa, AZ MSA AZ 3,251,876

8520 Tucson, AZ MSA AZ 843,746

680 Bakersfield, CA MSA CA 661,645

2840 Fresno, CA MSA CA 922,516

4480 Los Angeles--Long Beach, CA PMSA CA 9,519,338

5170 Modesto, CA MSA CA 446,997

5775 Oakland, CA PMSA CA 2,392,557

5945 Orange County, CA PMSA CA 2,846,289

6780 Riverside--San Bernardino, CA PMSA CA 3,254,821

6920 Sacramento, CA PMSA CA 1,628,197

7120 Salinas, CA MSA CA 401,762

7320 San Diego, CA MSA CA 2,813,833

7360 San Francisco, CA PMSA CA 1,731,183

7400 San Jose, CA PMSA CA 1,682,585

7480 Santa Barbara--Santa Maria--Lompoc, CA MSA CA 399,347

7500 Santa Rosa, CA PMSA CA 458,614

8120 Stockton--Lodi, CA MSA CA 563,598

8720 Vallejo--Fairfield--Napa, CA PMSA CA 518,821

8735 Ventura, CA PMSA CA 753,197

8780 Visalia--Tulare--Porterville, CA MSA CA 368,021

1720 Colorado Springs, CO MSA CO 516,929

2080 Denver, CO PMSA CO 2,109,282

1160 Bridgeport, CT PMSA CT 459,479

3280 Hartford, CT MSA CT 1,183,110

5480 New Haven--Meriden, CT PMSA CT 542,149

8040 Stamford--Norwalk, CT PMSA CT 353,556

8840 Washington, DC--MD--VA--WV PMSA DC/MD/VA/WV 4,923,153

9160 Wilmington--Newark, DE--MD PMSA DE/MD 586,216

2020 Daytona Beach, FL MSA FL 493,175

2680 Fort Lauderdale, FL PMSA FL 1,623,018

2700 Fort Myers--Cape Coral, FL MSA FL 440,888
21

3600 Jacksonville, FL MSA FL 1,100,491

3980 Lakeland--Winter Haven, FL MSA FL 483,924

4900 Melbourne--Titusville--Palm Bay, FL MSA FL 476,230

5000 Miami, FL PMSA FL 2,253,362

5960 Orlando, FL MSA FL 1,644,561

6080 Pensacola, FL MSA FL 412,153

7510 Sarasota--Bradenton, FL MSA FL 589,959

8280 Tampa--St. Petersburg--Clearwater, FL MSA FL 2,395,997

8960 West Palm Beach--Boca Raton, FL MSA FL 1,131,184

520 Atlanta, GA MSA GA 4,112,198

600 Augusta--Aiken, GA--SC MSA GA/SC 477,441

3320 Honolulu, HI MSA HI 876,156

2120 Des Moines, IA MSA IA 456,022

1960 Davenport--Moline--Rock Island, IA--IL MSA IA/IL 359,062

1080 Boise City, ID MSA ID 432,345

1600 Chicago, IL PMSA IL 8,272,768

6880 Rockford, IL MSA IL 371,236

2760 Fort Wayne, IN MSA IN 502,141

2960 Gary, IN PMSA IN 631,362

3480 Indianapolis, IN MSA IN 1,607,486

9040 Wichita, KS MSA KS 545,220

4280 Lexington, KY MSA KY 479,198

4520 Louisville, KY--IN MSA KY 1,025,598

760 Baton Rouge, LA MSA LA 602,894

3880 Lafayette, LA MSA LA 385,647

5560 New Orleans, LA MSA LA 1,337,726

7680 Shreveport--Bossier City, LA MSA LA 392,302

1120 Boston, MA--NH PMSA MA 3,406,829

8000 Springfield, MA MSA MA 591,932

9240 Worcester, MA--CT PMSA MA/CT 511,389

4160 Lawrence, MA--NH PMSA MA/NH 396,230

720 Baltimore, MD PMSA MD 2,552,994

440 Ann Arbor, MI PMSA MI 578,736

2160 Detroit, MI PMSA MI 4,441,551

2640 Flint, MI PMSA MI 436,141

3000 Grand Rapids--Muskegon--Holland, MI MSA MI 1,088,514
22

3720 Kalamazoo--Battle Creek, MI MSA MI 452,851

4040 Lansing--East Lansing, MI MSA MI 447,728

6960 Saginaw--Bay City--Midland, MI MSA MI 403,070

5120 Minneapolis--St. Paul, MN--WI MSA MN/WI 2,968,806

7040 St. Louis, MO--IL MSA MO/IL 2,603,607

3760 Kansas City, MO--KS MSA MO/KS 1,776,062

920 Biloxi--Gulfport--Pascagoula, MS MSA MS 363,988

3560 Jackson, MS MSA MS 440,801

3120 Greensboro--Winston-Salem--High Point, NC MSA NC 1,251,509

6640 Raleigh--Durham--Chapel Hill, NC MSA NC 1,187,941

1520 Charlotte--Gastonia--Rock Hill, NC--SC MSA NC/SC 1,499,293

5920 Omaha, NE--IA MSA NE/IA 716,998

560 Atlantic--Cape May, NJ PMSA NJ 354,878

875 Bergen--Passaic, NJ PMSA NJ 1,373,167

3640 Jersey City, NJ PMSA NJ 608,975

5015 Middlesex--Somerset--Hunterdon, NJ PMSA NJ 1,169,641

5190 Monmouth--Ocean, NJ PMSA NJ 1,126,217

5640 Newark, NJ PMSA NJ 2,032,989

8480 Trenton, NJ PMSA NJ 350,761

200 Albuquerque, NM MSA NM 712,738

4120 Las Vegas, NV--AZ MSA NV/AZ 1,563,282

160 Albany--Schenectady--Troy, NY MSA NY 875,583

1280 Buffalo--Niagara Falls, NY MSA NY 1,170,111

5380 Nassau--Suffolk, NY PMSA NY 2,753,913

5600 New York, NY PMSA NY 9,314,235

6840 Rochester, NY MSA NY 1,098,201

8160 Syracuse, NY MSA NY 732,117

5660 Newburgh, NY--PA PMSA NY/PA 387,669

80 Akron, OH PMSA OH 694,960

1320 Canton--Massillon, OH MSA OH 406,934

1680 Cleveland--Lorain--Elyria, OH PMSA OH 2,250,871

1840 Columbus, OH MSA OH 1,540,157

2000 Dayton--Springfield, OH MSA OH 950,558

8400 Toledo, OH MSA OH 618,203

9320 Youngstown--Warren, OH MSA OH 594,746

1640 Cincinnati, OH--KY--IN PMSA OH/KY/IN 1,646,395
23

5880 Oklahoma City, OK MSA OK 1,083,346

8560 Tulsa, OK MSA OK 803,235

6440 Portland--Vancouver, OR--WA PMSA OR/WA 1,918,009

240 Allentown--Bethlehem--Easton, PA MSA PA 637,958

3240 Harrisburg--Lebanon--Carlisle, PA MSA PA 629,401

4000 Lancaster, PA MSA PA 470,658

6280 Pittsburgh, PA MSA PA 2,358,695

6680 Reading, PA MSA PA 373,638

7560 Scranton--Wilkes-Barre--Hazleton, PA MSA PA 624,776

9280 York, PA MSA PA 381,751

6160 Philadelphia, PA--NJ PMSA PA/NJ 5,100,931

6360 Ponce, PR MSA PR 361,094

7440 San Juan--Bayamon, PR PMSA PR 1,967,627

6480 Providence--Fall River--Warwick, RI--MA MSA RI/MA 1,188,613

1440 Charleston--North Charleston, SC MSA SC 549,033

1760 Columbia, SC MSA SC 536,691

3160 Greenville--Spartanburg--Anderson, SC MSA SC 962,441

3840 Knoxville, TN MSA TN 687,249

5360 Nashville, TN MSA TN 1,231,311

4920 Memphis, TN--AR--MS MSA TN/AR/MS 1,135,614

1560 Chattanooga, TN--GA MSA TN/GA 465,161

3660 Johnson City--Kingsport--Bristol, TN--VA MSA TN/VA 480,091

640 Austin--San Marcos, TX MSA TX 1,249,763

840 Beaumont--Port Arthur, TX MSA TX 385,090

1880 Corpus Christi, TX MSA TX 380,783

1920 Dallas, TX PMSA TX 3,519,176

2320 El Paso, TX MSA TX 679,622

2800 Fort Worth--Arlington, TX PMSA TX 1,702,625

3360 Houston, TX PMSA TX 4,177,646

4880 McAllen--Edinburg--Mission, TX MSA TX 569,463

7240 San Antonio, TX MSA TX 1,592,383

6520 Provo--Orem, UT MSA UT 368,536

7160 Salt Lake City--Ogden, UT MSA UT 1,333,914

5720 Norfolk--Virginia Beach--Newport News, VA--NC 

MSA

VA/NC 1,569,541

6760 Richmond--Petersburg, VA MSA VA/NC 996,512

7600 Seattle--Bellevue--Everett, WA PMSA WA 2,414,616
24

7840 Spokane, WA MSA WA 417,939

8200 Tacoma, WA PMSA WA 700,820

460 Appleton--Oshkosh--Neenah, WI WI 358,365

4720 Madison, WI MSA WI 426,526

5080 Milwaukee--Waukesha, WI PMSA WI 1,500,741
25

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 

decisionmakers 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 
26

other 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 
27

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." 
28

United States 

Environmental Protection 

Agency 

Office of Air Quality Planning and 

Standards 

Research Triangle Park, NC 27711 

Publication No. EPA454/B-09-001

February 2009