Technical Assistance Document for the 

Reporting of Daily Air Quality – the Air Quality 

Index (AQI)

EPA 454/B-18-007

September 2018

Technical Assistance Document for the Reporting of Daily Air Quality – the Air Quality Index 

(AQI)

U.S. Environmental Protection Agency

Office of Air Quality Planning and Standards

Air Quality Assessment Division

Research Triangle Park, NC
CONTENTS

I. REPORTING THE AQI

II. CALCULATING THE AQI

III. FREQUENTLY ASKED QUESTIONS

IV. RESOURCES

LIST OF TABLES

Table 1. Names and colors for the six AQI categories

Table 2. AQI color formulas

Table 3. Pollutant-Specific Sensitive Groups

Table 4. Cautionary Statements

Table 5. Breakpoints for the AQI

LIST OF FIGURES

Figure 1. The AQI is reported in many formats

Figure 2. Display of AQI forecast

Figure 3. The NowCast

Figure 4. Airnow.gov page showing the AQI at U.S. Embassies and Consulates

Figure 5. The AQI on AirNow’s Fires: Current Conditions page

Figure 6. The AirNow widget
1

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

required in 40 CFR Part 58.50 and according to 40 CFR Appendix G to Part 58.

I. REPORTING THE AQI

Do I have to report the AQI?

Metropolitan Statistical Areas (MSAs) with a population of more than 350,000 are required to report the 

AQI daily to the general public. The population of an MSA for purposes of index reporting is based on 

the latest available U.S. census population. 

How often do I report the AQI?

MSAs must report the AQI daily, which is defined as at least five days each week. This definition allows 

for days when personnel are not available to provide the AQI report or for equipment failures.

What goes in my AQI report?

Required reporting: 

It takes a full 24 hours to obtain an AQI value (that’s 24 hourly values for PM or the max 1-hour or 8-

hour value in a 24-hour period for other pollutants), so you are in effect required to report yesterday’s 

AQI, including:

• the reporting area

• the reporting period 

• the critical pollutant (the pollutant with the highest AQI value)

• the AQI value

• the category descriptor and color (if your report uses color) shown in Table 1

• the sensitive groups for all pollutants with an AQI over 100, as shown in Table 3

Voluntary reporting:

To make AQI reporting more useful to the public, most agencies also choose to report some or all of the 

following: 

• Forecast and current AQI values

• Health effects and cautionary statements 

• Causes for unusual AQI values

• The AQI for sub-areas of the reporting area

• Pollutant concentrations

• The name and AQI for other pollutants, particularly those with an AQI greater than 100

• Statements that “blend” health effects and cautionary information for more than one 

pollutant, if there is more than one pollutant with an AQI greater than 100
2

Table 1. 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 to 500 Hazardous Maroon

Note: Values above 500 are considered “Beyond the AQI.” Follow recommendations for the Hazardous 

category. 

How are the AQI colors defined?

The colors are defined by the formulas RGB (red, green, blue) and CMYK (cyan, magenta, yellow, black) 

as shown in Table 2.

Table 2. AQI 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: RGB is traditionally used for screen colors, while CMYK is traditionally used for printing. The color 

models are based on a 0 - 255 scale (e.g. 50% is 126).
3

Table 3. Pollutant-Specific Sensitive Groups

When this pollutant 

has an AQI above 100...

Report these Sensitive Groups

Ozone People with lung disease, children, older adults, people who are active 

outdoors (including outdoor workers), people with certain genetic variants, 

and people with diets limited in certain nutrients are the groups most at 

risk

PM2.5 People with heart or lung disease, older adults, children, and people of 

lower socioeconomic status 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 is 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

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

What cautionary statements should I use in my AQI report?

Table 4 lists cautionary statements for each pollutant.
4

Table 4. 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] PM2.5 [24-hour] PM10 [24-hour]

Good

(Up to 50)

0 - 0.054

None

0 – 12.0

None

0 - 54

None

0 – 4.4

None

0 - 35

None

0 - 53

None

Moderate

(51 - 100)

0.055 - 0.070 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)

0.071 - 0.085 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, people who are active 

outdoors (including outdoor workers), people 

with certain genetic variants, and people with 

diets limited in certain nutrients should reduce 

prolonged or heavy outdoor exertion.

People with heart or lung disease, older adults, 

children, and people of lower socioeconomic status 

should reduce prolonged or heavy exertion.
5

Unhealthy

(151 - 200)

0.086 - 0.105 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, people who are active 

outdoors (including outdoor workers), people 

with certain genetic variants, and people with 

diets limited in certain nutrients 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 socioeconomic status 

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)

0.106 - 0.200 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, people who are active 

outdoors (including outdoor workers), people 

with certain genetic variants, and people with 

diets limited in certain nutrients should avoid 

all outdoor exertion; everyone else should 

reduce outdoor exertion.

People with heart or lung disease, older adults, 

children, and people of lower socioeconomic status 

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.

605 – 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 socioeconomic status 

should remain indoors and keep activity levels low.
6

What health effects and cautionary statements should I use if the AQI goes above 500?

If the AQI is higher than 500, it is called “Beyond the AQI.” Use the same information that is for the 

Hazardous category. 

Do I have to report the AQI if my values are low?

If the AQI values for all of the pollutants remain below 50 for a year, then you may report the AQI at 

your discretion. In subsequent years, if any pollutant level rises to where the AQI would be above 50, 

then you must report the AQI.

If a specific pollutant remains below 50 for an extended period of time (a season or a year), you may 

exclude that pollutant from your AQI calculation.

How is the AQI reported?

AQI reports take many forms 

– from traditional media like 

television, newspaper, radio, 

and phone, to more digital 

forms such as widgets, apps, 

web pages, and social media. 

The purpose of the AQI is to 

inform people about their air 

quality so they can take steps 

to protect their health. This is 

especially important 

whenever the AQI exceeds 

100. To reach the most 

people, try to deliver the AQI 

in as many ways as possible.

Figure 1. The AQI is reported in many formats.

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.
7

Do I have to forecast the AQI?

Forecasting is encouraged, but it is not required. A prediction for the 

next day or several days allows people to plan their activities so that 

they can reduce or avoid exposure to air pollution. Good forecasts 

require data, computational resources, and expertise. EPA provides 

guidance if you are interested in starting a forecasting program. For 

more information, see Guidelines for Developing an Air Quality 

Forecasting Program in the Resources section. 

Figure 2. Display of AQI forecast

Do I need to have air quality action days as part of my program?

No. The use of air quality action days or community action programs, which are usually based on AQI 

forecasts, is voluntary. However, action days and similar programs can provide significant benefits, 

especially when they directly and effectively communicate to at-risk groups about air quality and 

associated health effects. Air quality action days may be called by state or local air agencies when the 

AQI will get into the unhealthy ranges. Different agencies call them at different levels, such as Orange or 

Red or sometimes Yellow. 

How is the AQI reported in real time?

EPA uses the NowCast to approximate the complete daily AQI during any given hour. Even on days when 

the AQI forecast predicts unhealthy conditions, pollution levels may be lower and better for outdoor 

activities during some parts of the day. Providing current conditions gives people the power to take 

action to reduce outdoor activities and exposure when necessary and protect their health. 

The NowCast calculation uses longer averages during periods of stable air quality and shorter averages 

when air quality is changing rapidly, such as during a fire. The NowCast allows current conditions maps 

to align more closely with what people are actually seeing or experiencing.

Figure 3. The NowCast

NowCast

less variable air quality more variable air quality

Longer term average

Ozone: ~8 hours

PM2.5: ~12 hours

PM10: ~12 hours

Real-time

Ozone: ~1 hour

PM2.5: ~3 hours

PM10: ~3 hours
8

How can AirNow help?

EPA’s AirNow accepts, stores, and displays air quality data from state and local air quality agencies.

Here’s some of what you’ll find at airnow.gov:

• National, regional, and local air quality maps

• AQI forecasts and current conditions

• Yesterday’s AQI and archives of AQI data

• Health and educational information

• AirNow Application Program Interface (API) for access to real-time data and 

forecasts. The API can be used to feed apps, web sites, and other data systems

• Access to AirNow app and widgets

• Enviroflash - sign up to get air quality info by email 

• The AQI from both regulatory and temporary monitors located near current fires

• The AQI reported abroad at U.S. embassies and consulates, courtesy of the U.S. Department of 

State 

Figure 4. Airnow.gov page showing the AQI at U.S. 

Embassies and Consulates

Figure 5. The AQI on AirNow’s Fires: 

Current Conditions page

Figure 6. The AirNow widget
9

II. CALCULATING THE AQI

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 (ppm) – truncate to 3 decimal places

PM2.5 (μg/m3

) – truncate to 1 decimal place

PM10 (μg/m3

) – truncate to integer

CO (ppm) – truncate to 1 decimal place

SO2 (ppb) – truncate to integer

NO2 (ppb) – truncate to integer

b. Using Table 5, 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: 

Where Ip = the index for pollutant p

Cp = the truncated concentration of pollutant p

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

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

 IHi = the AQI value corresponding to BPHi

ILo = the AQI value corresponding to BPLo

I I I

BP BP (C BP ) I . p

Hi Lo

HI Lo

=

p Lo Lo

−

− − +
10

Table 5: Breakpoints for the AQI

These Breakpoints... ...equal 

this AQI

...and this 

category

O3

(ppm)

8-hour

O3

(ppm)

1-hour1

PM2.5

(μg/m3

)

24-hour

PM10

(μg/m3

)

24-hour

CO

(ppm)

8-hour

SO2

(ppb)

1-hour

NO2

(ppb)

1-hour

AQI

0.000 -

0.054

- 0.0 – 12.0 0 - 54 0.0 - 4.4 0 - 35 0 - 53 0 - 50 Good

0.055 -

0.070

- 12.1 –

35.4

55 - 154 4.5 - 9.4 36 - 75 54 - 100 51 - 100 Moderate

0.071 -

0.085

0.125 -

0.164

35.5 –

55.4

155 - 254 9.5 - 12.4 76 - 185 101 - 360 101 - 150 Unhealthy for 

Sensitive Groups

0.086 -

0.105

0.165 -

0.204

(55.5 -

150.4)3

255 - 354 12.5 -

15.4

(186 -

304)4

361 - 649 151 - 200 Unhealthy

0.106 -

0.200

0.205 -

0.404

(150.5 -

(250.4)3

355 - 424 15.5 -

30.4

(305 -

604)4

650 -

1249

201 - 300 Very unhealthy

(

2

) 0.405 -

0.504

(250.5 -

(350.4)3

425 - 504 30.5 -

40.4

(605 -

804)4

1250 -

1649

301 - 400 Hazardous

(

2

) 0.505 -

0.604

(350.5 -

500.4)3

505 - 604 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.
11

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 0.07853333. First, truncate the value to 0.078. Then refer 

to the 8-hour ozone in table 5 for the values that fall above and below your value (0.071-0.085). In this 

case, the 0.078 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 0.07853333 corresponds to an index value of 126.

What if I have values for more pollutants?

Suppose you have an 8-hour ozone value of 0.078 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 126, 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 0.162 ppm and an 8-hour value of 0.078 ppm. Then you apply the 

equation twice:

In this case, the index is 148 (the maximum of 148 and 126) and the responsible pollutant is ozone.

1 150 101

164 125 162 125 101 148

8 150 101

085 071 078 071 101 126

− −

− − + =

− −

− − + =

hr

hr

:

( )

(. . )

(. . )

:

( )

(. . )

(. . )

O

PM

CO

3

150 101

085 071

078 071 101 126

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

085 071

078 071 101

49

014

007 101 125.5 126 −

− − + = + = =
12

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 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 5 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 5 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 0.104 ppm and an 8-hour ozone 

value of 0.078 ppm. 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:

( )

(. . )

(. . )

150 101

085 071

078 071 101 126 −

− − + =
13

III. FREQUENTLY ASKED QUESTIONS

Q. Why doesn’t my area report an Air Quality Index value?

A. Towns and cities with 350,000 or fewer inhabitants are not required to report the AQI. Some may not 

have monitors. In addition, AirNow is a voluntary program and some state or local air quality monitoring 

agencies may not submit data to AirNow. 

Q. 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?

A. If this was an AQI forecast, there are still a few areas of the United States that only forecast for ozone 

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

conditions experienced were due to particle pollution. In this instance, the reported AQI forecast may 

have only represented ozone.

There are also 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.

Q. How do I get my local media outlets to show the AQI?

A. Many local media outlets choose to display the AQI as part of their weather reports. The text and 

graphics they use are usually developed and produced by private weather service companies, who have 

access to air quality data through AirNow. Try approaching the media person who is the customer of the 

weather service provider. This could be a newspaper editor or the television or radio station manager.

In general, media outlets want to provide more health-based information to their readers. However, it 

may take some effort to establish a relationship and educate decision makers about the importance of 

providing air quality information to the public. When you meet with them, bring along this guidance 

document or several examples showing how other media outlets publish the AQI. Emphasize that air 

quality is weather, news and health all in one. Make sure they have the proper software to access and 

display the data from the weather service company. Keep in mind that they may want to display air 

quality information only during periods of high pollution levels, when it is considered more newsworthy.

Q. If the AQI reported in the local media is incorrect, what should I do?

A. Common problems with AQI reporting in the local media 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 local media and educating them about how misleading or erroneous AQI 

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

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

service provider as a paying customer. If you have difficulty getting the media outlet to correct the issue, 

you could team with other health and nongovernmental organizations to approach them with a united 

message and request.
14

Q. Can AirNow help me meet the reporting requirements for the AQI?

A. AirNow is one way you can submit, store, and display your AQI values. This includes the required 

elements of AQI reporting and the voluntary elements. The information you submit to airnow.gov is 

reported in national and state/local pages on the website. It is available to anyone through the airnow 

app and widget and Enviroflash emails. It is also available for distribution to media and weather service 

provider companies. 

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

A. 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/.

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

A. 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 pollutantsground-level ozone, particle pollution, carbon monoxide, sulfur dioxide, and nitrogen dioxide.

Q. What is the NowCast and what does it have to do with the AQI?

A. The Air Quality Index is based on daily air quality summaries, specifically daily maximums or daily 

averages. It is not valid to use shorter-term (e.g. hourly) data to calculate an AQI value. However, realtime reporting requires shorter-term data to caution people in time for them to reduce their 24-hour 

exposure. The NowCast is EPA’s endorsed method for relating short-term (less than 24-hour) data to 

the Air Quality Index for the purposes of real-time reporting.

Q. How is the AQI computed when the pollutant concentrations are beyond the Hazardous category

(AQI above 500)?

A. When concentrations are above the range of the Hazardous category, they are called “Beyond the 

AQI”. However, an AQI value can still be computed to indicate relative magnitude. To do this, use the 

same linear relationship that is used for the Hazardous category. Use the regular formula for computing 

an AQI value and use the Hazardous category breakpoints in the calculation.

Q. How are “Beyond the AQI” values (AQI above 500) handled in the NowCast?

A. They are not handled differently. Compute the NowCast concentration as you normally would and 

use the Hazardous category breakpoints to compute the NowCast AQI value.
15

Q. What should people do if the AQI is above 500?

A. If the AQI is higher than 500, it is called “Beyond the AQI.” Follow the recommendations for the 

Hazardous category. Everyone should take steps to reduce their exposure. Stay indoors – in a room or 

building with filtered air – and reduce activity levels to reduce the amount of pollution you breathe into 

your lungs. 

Q. How is the ozone AQI calculation affected by the revision of the ozone standard?

A. When the ozone standard was revised in 2015, the data handling for the daily max was modified to 

use only the 8-hour averages starting at 7am. This was done to avoid double-counting an exceedance 

from a single, short-term episode that spans the nighttime hours of the first day into the early hours of 

the second day. The daily maximum 8-hour average used for computing the AQI value is the same daily 

maximum 8-hour average described in the data handling for the revised ozone standard (i.e. it is based 

on the 17 consecutive moving 8-hour periods in each day, beginning with the 8-hour period from 7am to 

3pm, and ending with the 8-hour period from 11pm to 7am).

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

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

pollution” than "particulate matter."

Q. Why are some people using low-cost, compact sensors to measure air quality?

A. Many citizens are interested in learning more about local air quality where they live, work, and play. 

Low-cost, compact, sometimes-portable sensors are becoming more popular for collecting real-time 
16

(usually 1-minute) air quality data. EPA scientists created the Air Sensor Toolbox for Citizen Scientists to 

provide information about sensor performance and how to interpret the data from sensors.

Learn more at http://www.epa.gov/air-research/air-sensor-toolbox-citizen-scientists

Q. Can I apply the AQI colors to 1-minute data from low-cost air quality sensors? 

A. No. Sensors generally report 1-minute data, and health studies do not tell us what a single minute of 

exposure to a pollutant may mean. The AQI is based on EPA’s national air quality standards, which come 

from health studies that show the effects of longer exposures. 

Q. What does the Village Green Project do?

A. The Village Green Project is an innovative prototype air and weather measurement system built into a 

park bench. The station engages communities in air pollution awareness at a local level. The pilot station 

in Durham, North Carolina monitors several common air pollutants in real-time and makes the data 

available online and by smartphone. The solar and wind powered station provides minute-to-minute air 

measurements for ozone, particle pollution and weather conditions. The Village Green Project is 

expanding to other communities across the U.S.

Learn more at http://www.epa.gov/air-research/village-green-project

Q. What is the ozone monitoring season for each state?

A. EPA requires ozone monitoring during the time of year when weather conditions are most favorable 

for ozone formation. This season varies by state. In some states with warmer climates, monitoring is 

required year-round. In states where the climate is colder, ozone monitoring is required for as little as 

five months during the summertime. You can find a list of ozone monitoring seasons by state in 40 CFR 

Part 58 Appendix D, Table D-3.
17

IV. RESOURCES

AQI Final Rule 64 FR 42530, August 4 1999: http://www3.epa.gov/ttn/oarpg/t1/fr_notices/airqual.pdf

Guidelines for Developing an Air Quality Forecasting Program:

http://www3.epa.gov/airnow/aq_forecasting_guidance-1016.pdf. 

Air Sensor Toolbox for Citizen Scientists:

http://www.epa.gov/air-research/air-sensor-toolbox-citizen-scientists

EPA’s National Air Toxics Assessment (NATA): https://www.epa.gov/national-air-toxics-assessment

Fires and Your Health: https://www.airnow.gov/index.cfm?action=topics.smoke_events

Air quality outreach materials in English and Spanish:

https://airnow.gov/index.cfm?action=pubs.index

https://airnow.gov/index.cfm?action=pubs_spanish.index

Basic information on the AQI in Spanish:

https://www.airnow.gov/index.cfm?action=aqibasics.aqi_sp

List of monitoring season by state in 40 CFR Part 58 Appendix D, Table D-3:

http://www.ecfr.gov/cgi-bin/retrieveECFR?gp=&r=PART&n=40y6.0.1.1.6

EPA’s Air Quality Flag Program: https://www.airnow.gov/index.cfm?action=flag_program.index

Village Green Project: http://www.epa.gov/air-research/village-green-project
United States

Environmental Protection

Agency

Office of Air Quality Planning and Standards

Air Quality Assessment Division

Research Triangle Park, NC

Publication No. EPA-454/B-18-007

September 2018