Technical Assistance Document for the
Reporting of Daily Air Quality - the Air Quality
Index (AQI)
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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
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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
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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
1
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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).
2
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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
N02
People with asthma, children, and older adults are the groups most at risk
SO 2
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.
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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 (jjg/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.
4
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Unhealthy
0.086-0.105
0.165-0.204
55.5-150.4
255 - 354
12.5-15.4
186-304
361 - 649
(151 -200)
People with lung disease (such as asthma),
People with heart or lung disease, older adults,
People with heart
Children, people with
People with asthma,
children, older adults, people who are active
children, and people of lower socioeconomic status
disease, such as
asthma, or other lung
children and older
outdoors (including outdoor workers), people
should avoid prolonged or heavy exertion; everyone
angina, should limit
diseases, should limit
adults should avoid
with certain genetic variants, and people with
else should reduce prolonged or heavy exertion.
moderate exertion and
outdoor exertion.
prolonged exertion near
diets limited in certain nutrients should avoid
avoid sources of CO,
roadways; everyone
prolonged or heavy outdoor exertion;
such as heavy traffic.
else should limit
everyone else should reduce prolonged or
prolonged exertion
heavy outdoor exertion
especially near busy
roads.
Very Unhealthy
0.106-0.200
0.205 - 0.404
150.5-250.4
355 - 424
15.5-30.4
305 - 604 [24-hour]
650- 1249
(201 - 300)
People with heart
Children, people with
People with asthma,
disease, such as
asthma, or other lung
children and older
People with lung disease (such as asthma),
People with heart or lung disease, older adults,
angina, should avoid
diseases should avoid
adults should avoid all
children, older adults, people who are active
children, and people of lower socioeconomic status
exertion and sources of
outdoor exertion;
outdoor exertion;
outdoors (including outdoor workers), people
should avoid all physical activity outdoors. Everyone
CO, such as heavy
everyone else should
everyone else should
with certain genetic variants, and people with
else should avoid prolonged or heavy exertion.
traffic.
reduce outdoor exertion.
avoid prolonged
diets limited in certain nutrients should avoid
exertion especially near
all outdoor exertion; everyone else should
busy roads.
reduce outdoor exertion.
Hazardous
.
0.405 - 0.604
250.5 - 500.4
425 - 604
30.5 - 50.4
605-1004 [24-hour]
1250-2049
(301 - 500)
People with heart
Children, people with
People with asthma,
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.
disease, such as
angina, should avoid
exertion and sources of
CO, such as heavy
traffic; everyone else
asthma, or other lung
diseases, should remain
indoors; everyone else
should avoid outdoor
exertion.
children and older
adults should remain
indoors; everyone else
should avoid all outdoor
exertion.
should limit heavy
exertion.
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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.
Previously Observed Today's Forecast Tomorrow's Forecast
Air Quality observed on Wednesday, 02/03/2016 {Chargeaas)
Current Air Quality
in Moreno Valley is
GOOD
$ VIEW FULL MAP
Air Quality Index
Yessrda/s report 66
Mam pollutant Particulate Matter
Air GuaBty for Raleigh. N.C.
0-50
51-100
101-150
201-300
Good
Moderate
Unhealthy,
groups
unhealthy
Tcday's ozone 38
Weather ~r
St. „ - T
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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.
Figure 1. The AQI is reported in many formats.
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Do I have to forecast the AQI?
Air Quality Forecast
Wednesday r
February 3 at 9:09 AM
59 57
55 55
Central Bay
Eastern District
B1 53
South Central
Bay
ill KIM
Santa Clara
Valley
W. \ "a fri'l
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.
less variable air quality
i
more variable air quality
I
Longer term average
Ozone: ~8 hours
PM2.5: ~12 hours
PM10: ~12 hours
NowCast
Real-time
Ozone: ~1 hour
PM2.5: ~3 hours
PM10: ~3 hours
Figure 3. The NowCast
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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
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Figure 4. Airnow.gov page showing the AQI at U.S.
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Figure 6. The AirNow widget
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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 (ng/m3) - truncate to 1 decimal place
PM 10 (M-g/m3) — truncate to integer
CO (ppm) - truncate to 1 decimal place
S02 (ppb)-truncate to integer
N02 (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 lp = 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
lHi = the AQI value corresponding to BPHi
lLo = the AQI value corresponding to BPLo
I
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Table 5: Breakpoints for the AQI
These Breakpoints...
...equal
this AQI
...and this
category
03
(PPm)
8-hour
O3
(ppm)
1-hour1
PM2.5
(Hg/m3)
24-hour
PM10
(Hg/m3)
24-hour
CO
(ppm)
8-hour
S02
(ppb)
1-hour
N02
(ppb)
1-hour
AQI
0.000 -
0.054
-
0.0-12.0
0-54
O
O
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 03 values do not define higher AQI values (> 301). AQI values of 301 or higher are calculated
with 1-hour 03 concentrations.
3 If a different SHL for PM2.5 is promulgated, these numbers will change accordingly.
4 1-hour S02 values do not define higher AQI values (> 200). AQI values of 200 or greater are calculated
with 24-hour S02 concentrations.
10
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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.
(150-101) 49
-(.078-071) +101 = .007 +101 = 125.5 = 126
(.085-071)v 7 .014
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 ng/m3, and a CO value of
8.4 ppm. You apply the equation 3-times:
(150-101)
(.085-071)(
°v 7^r^TTC078~071)+101=126
(150-101)
PM- — -(35.9 —35 5)+ 101 =102
(55.4-35.5) V J
(100-51)
CO: -(8.4 -4.5) + 51 = 90
(9.4-4.5)v ;
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:
i~kr: SUii(i62-i25)+101=148
^ S^(o78-°7i)+ioi=i26
In this case, the index is 148 (the maximum of 148 and 126) and the responsible pollutant is ozone.
11
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How do I calculate AQI values for S02?
EPA strengthened the primary standard for S02 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 S02 concentration. The lower end of the AQI uses the daily max 1-hour S02
concentration.
If you have a daily max 1-hour S02 concentration below 305 ppb, then use the breakpoints in Table 5 to
calculate the AQI value.
If you have a 24-hour average S02 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
12
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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.
13
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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 pollutants-
ground-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, real-
time 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.
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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).
Previous 8-hour ozone standards
Day
12
1 2
3
4
5 6 7
8 9
10
11
" i
pm
2 3 4
5 6
7
8 9
10 11
12
1
2 3
4 5 6
Day
2
12
am
1
2 3
4 5 6
~ Previous ozone standards considered 24 overlapping 8-hour averages
The first 8-hour average began at 12am and ended at 7:59 am and the last began at 11pm and ended at 6:59 am of the next day.
• Because the 8-hour averages for each day started at 12am, the hours from 12am to 6:59am were "double counted."
This double-counting could result in daily exceedances on different days influenced by the same hours.
New (2015) 8-hour ozone standards
Day
0
12 .
am
1 2 3
4
5
6
Day
1
7 {
1 9 10 11 " 1
pm
2
3
4
5
&
7 i
> 9 10 11 " 1
am
2
3
4
5
6
Day
2
7
8
9 10
The new ozone standards eliminate double counting by starting the daily averages at 7am every day.
The first 8-hour average begins at 7am and ends at 2:59 pm and the last begins at 11pm and ends at 6:59 am of the next day.
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
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(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-proiect
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.
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IV. RESOURCES
AQI Final Rule 64 FR 42530, August 4 1999: http://www3.epa.gov/ttn/oarpg/tl/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=40v6.0.1.1.6
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-proiect
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United States Office of Air Quality Planning and Standards Publication No. EPA-454/B-18-007
Environmental Protection Air Quality Assessment Division September 2018
Agency Research Triangle Park, NC
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