Technical Assistance Document
for the Reporting of Daily Air Quality -
the Air Quality Index (AQI)
May 2016
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EPA-454/B-16-002
May 2016
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
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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. Health Effects Statements
Table 5. Cautionary Statements
Table 6. 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...
OtoSO
51 to 100
101 to 150
151 to 200
201 to 300
301 to 500
use this descriptor...
Good
Moderate
Unhealthy for Sensitive Groups
Unhealthy
Very Unhealthy
Hazardous
and this color
Green
Yellow
Orange
Red
Purple
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
B
M
K
228
255
126
0
63
0
0
0
0
0
151
35
40
0
0
0
51
30
0
0
52
100
89
100
100
100
100
100
0
100
0
0
0
0
0
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).
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Table 3. Pollutant-Specific Sensitive Groups
When this pollutant
has an AQI above 100...
Ozone
PM2.5
PM10
CO
NO2
SO 2
Report these Sensitive Groups
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
People with heart or lung disease, older adults, children, and people of
lower socioeconomic status are the groups most at risk
People with heart or lung disease, older adults, children, and people of
lower socioeconomic status are the groups most at risk
People with heart disease is the group most at risk
People with asthma, children, and older adults are the groups most at risk
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 health effects and cautionary statements should I use in my AQI report?
Tables 4 and 5 list all the health effects messages, sensitive groups, and cautionary statements for each
pollutant.
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Table 4. Pollutant-Specific Sub-indices and Health Effects Statements
for Guidance on the Air Quality Index (AQI)
AQI
Categories:
Index Values
Good
(Up to 50)
Moderate
Unhealthy for
Sensitive Groups
(101 -150)
Ozone (ppm)
[8-hour]
0 - 0.054
None
0.055 - 0.070
Unusually sensitive
individuals may
experience respiratory
symptoms.
0.071 - 0.085
[1-hour]
-
-
0.125-0.164
Increasing likelihood of respiratory symptoms
and breathing discomfort in 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.
Particulate Matter (ug/m3)
PM2 5 [24-hour]
0-12.0
None
12.1 -35.4
PM10 [24-hourl
0-54
None
55-154
Respiratory symptoms possible in unusually
sensitive individuals; possible aggravation of heart
or lung disease in people with cardiopulmonary
disease and older adults.
35.5 - 55.4
155-254
Increasing likelihood of respiratory symptoms in
sensitive groups including older adults, children,
and people of lower socioeconomic status;
aggravation of heart or lung disease and premature
mortality in people with heart or lung disease
Carbon Monoxide
(ppm)
[8-hour]
0-4.4
None
4.4-9.4
9.5-12.4
Increasing likelihood of
reduced exercise
tolerance due to
increased
cardiovascular
symptoms, such as
chest pain, in people
with heart disease.
Sulfur Dioxide
(PPb)
[1-hour]
0-35
None
36-75
76-185
Increasing likelihood of
respiratory symptoms,
such as chest tightness
and breathing discomfort,
in people with asthma.
Nitrogen Dioxide
(PPb)
[1-hour]
0-53
None
54-100
101 -360
Increasing likelihood of
respiratory symptoms,
such as chest tightness
and breathing
discomfort, in people
with asthma.
-------
Unhealthy
(151 -200)
Very Unhealthy
/orn Qnn\
(ZU1 - oUUJ
Hazardous
(301 - 500)
0.086-0.105
0.165-0.204
Greater likelihood of respiratory symptoms and
breathing in 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;
possible respiratory effects in general
population.
0.106-0.200
0.205 - 0.404
Increasingly severe symptoms and impaired
breathing likely in 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; increasing likelihood of
respiratory effects in general population.
-
0.405 - 0.604
Severe respiratory effects and impaired
breathing likely in 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; increasingly severe
respiratory effects likely in general population.
55.5-150.4
255 - 354
Increased aggravation of respiratory symptoms in
sensitive groups including older adults, children,
and people of lower socioeconomic status;
increased aggravation of heart or lung disease and
premature mortality in people with heart or lung
disease; increased respiratory effects in general
population.
150.5-250.4
355 - 424
Significant aggravation of respiratory symptoms in
sensitive groups including older adults, children,
and people of lower socioeconomic status;
significant aggravation of heart or lung disease and
premature mortality in people with heart or lung
disease; significant increase in respiratory effects in
general population.
250.5 - 500.4
425 - 604
Serious aggravation of respiratory symptoms in
sensitive groups including older adults, children,
and people of lower socioeconomic status; serious
aggravation of heart or lung disease and premature
mortality in people with heart or lung disease;
serious risk of respiratory effects in general
population.
12.5-15.4
Reduced exercise
tolerance due to
increased
cardiovascular
symptoms, such as
chest pain, in people
with heart disease.
15.5-30.4
Significant aggravation
of cardiovascular
symptoms, such as
chest pain, in people
with heart disease.
30.5 - 50.4
Serious aggravation of
cardiovascular
symptoms, such as
chest pain, in people
with heart disease;
impairment of strenuous
activities in general
population.
186-304
Increased respiratory
symptoms, such as chest
tightness and wheezing
in people with asthma;
possible aggravation of
other lung diseases.
305 - 604 [24-hour]
Significant increase in
respiratory symptoms,
such as wheezing and
shortness of breath, in
people with asthma;
aggravation of other lung
diseases.
605 -1004 [24-hour]
Severe respiratory
symptoms, such as
wheezing and shortness
of breath, in people with
asthma; increased
aggravation of other lung
diseases; possible
respiratory effects in
general population.
361 - 649
Increased respiratory
symptoms, such as
chest tightness and
wheezing in people with
asthma; possible
aggravation of other
lung diseases.
650-1249
Significant increase in
respiratory symptoms,
such as wheezing and
shortness of breath, in
people with asthma;
aggravation of other
lung diseases.
1250-2049
Severe respiratory
symptoms, such as
wheezing and shortness
of breath, in people with
asthma; increased
aggravation of other
lung diseases; possible
respiratory effects in
general population.
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Table 5. Pollutant-Specific Sub-indices and Cautionary Statements
for Guidance on the Air Quality Index (AQI)
AQI
Categories
(Index
Values)
Good
(Up to 50)
Moderate
(51 - 100)
Unhealthy for
Sensitive Groups
(101 - 150)
Ozone (ppm)
[8-hour]
0 - 0.054
None
0.055 - 0.070
Unusually sensitive
people should
consider reducing
prolonged or heavy
outdoor exertion.
0.071 - 0.085
[1-hour]
0.125-0.164
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.
Particulate Matter (ug/m3)
PM, . [24-hour]
z.o
0-12.0
None
12.1 -35.4
PM10 [24-hourl
0-54
None
55-154
Unusually sensitive people should consider
reducing prolonged or heavy exertion.
35.5 - 55.4
155-254
People with heart or lung disease, older adults,
children, and people of lower socioeconomic status
should reduce prolonged or heavy exertion.
Carbon Monoxide
(ppm)
[8-hour]
0-4.4
None
4.5-9.4
None
9.5-12.4
People with heart
disease, such as
angina, should limit
heavy exertion and
avoid sources of CO,
such as heavy traffic.
Sulfur Dioxide
(PPb)
[1-hour]
0-35
None
36-75
None
76-185
People with asthma
should consider limiting
outdoor exertion.
Nitrogen Dioxide
(PPb)
[1-hour]
0-53
None
54-100
Unusually sensitive
individuals should
consider limiting
prolonged exertion
especially near busy
roads.
101 -360
People with asthma,
children and older
adults should limit
prolonged exertion
especially near busy
roads.
-------
Unhealthy
(151 -200)
Very Unhealthy
(201 - 300)
Hazardous
(301 - 500)
0.086-0.105
0.165-0.204
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
0.106-0.200
0.205 - 0.404
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.
_
Everyone should avoid
0.405 - 0.604
all outdoor exertion.
55.5-150.4
255 - 354
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.
150.5-250.4
355 - 424
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.
250.5 - 500.4
425 - 604
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.
12.5-15.4
People with heart
disease, such as
angina, should limit
moderate exertion and
avoid sources of CO,
such as heavy traffic.
15.5-30.4
People with heart
disease, such as
angina, should avoid
exertion and sources of
CO, such as heavy
traffic.
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.
186-304
Children, people with
asthma, or other lung
diseases, should limit
outdoor exertion.
305 - 604 [24-hour]
Children, people with
asthma, or other lung
diseases should avoid
outdoor exertion;
everyone else should
reduce outdoor exertion.
605 -1004 [24-hour]
Children, people with
asthma, or other lung
diseases, should remain
indoors; everyone else
should avoid outdoor
exertion.
361 - 649
People with asthma,
children and older
adults should avoid
prolonged exertion near
roadways; everyone
else should limit
prolonged exertion
especially near busy
roads.
650-1249
People with asthma,
children and older
adults should avoid all
outdoor exertion;
everyone else should
avoid prolonged
exertion especially near
busy roads.
1250-2049
People with asthma,
children and older
adults should remain
indoors; everyone else
should avoid all outdoor
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 ;;nr.j,::
Current Air Quality
in Moreno Valley is
GOOD
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Do I have to forecast the AQI?
2 Day Forecast
Air Quality Forecast
Wednesday, February 3 at 9;09 AM
North Counties
Coast and
Central Bay
Eastern District
South Central
Bay
Santa Clara
Valley
59
57
55
55
53
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
more variable air quality
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
Figure 4. Airnow.gov page showing the AQI at U.S.
Embassies and Consulates
HOW
or
••-! 27709
The Air Quality Index (AQI) for
Raleigh-Durham-Chapel Hill, NC
Today's Today's
Forecast Forecast
2/3/2016 2/3/2016
Pollutant: Pollutant:
Fires: Current Conditions
PM2.5
OZONE
0 O
Good Good
Figure 5. The AQI on AirNow's F/res:
Current Conditions page
Figure 6. The AirNow widget
10
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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.s (u.g/m3) - truncate to 1 decimal place
PMio (u.g/m3) - truncate to integer
CO (ppm) - truncate to 1 decimal place
SO2 (ppb)-truncate to integer
NO2 (ppb) -truncate to integer
b. Using Table 6, 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:
TLo
ffl LO
Where lp = the index for pollutant p
Cp = the truncated concentration of pollutant p
BPm = 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
11
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Table 6: Breakpoints for the AQI
These Breakpoints...
03
(ppm)
8-hour
0.000 -
0.054
0.055 -
0.070
0.071-
0.085
0.086 -
0.105
0.106-
0.200
(2)
(2)
03
(ppm)
1-hour1
-
-
0.125-
0.164
0.165-
0.204
0.205 -
0.404
0.405 -
0.504
0.505-
0.604
PM2.5
(ug/m3)
24-hour
0.0-12.0
12.1-
35.4
35.5-
55.4
(55.5 -
150.4)3
(150.5-
(250.4)3
(250.5-
(350.4)3
(350.5-
500.4)3
PMio
(ug/m3)
24-hour
0-54
55 - 154
155 - 254
255-354
355-424
425 - 504
505-604
CO
(ppm)
8-hour
0.0-4.4
4.5-9.4
9.5-12.4
12.5-
15.4
15.5-
30.4
30.5-
40.4
40.5-
50.4
S02
(ppb)
1-hour
0-35
36-75
76 - 185
(186-
304)4
(305-
604)4
(605-
804)4
(805-
1004)4
NO2
(ppb)
1-hour
0-53
54 - 100
101-360
361-649
650-
1249
1250-
1649
1650-
2049
...equal
this AQI
AQI
0-50
51-100
101 - 150
151-200
201-300
301-400
401-500
...and this
category
Good
Moderate
Unhealthy for
Sensitive Groups
Unhealthy
Very unhealthy
Hazardous
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.
12
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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 2 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) .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 u.g/m3, and a CO value of
8.4 ppm. You apply the equation 3-times:
(150-101)
a: -(.078-071) +101= 126
3 (.085-071)v '
(150-101)
PM- — -(35.9 -35 5) +101 =102
(55.4-35.5) V ;
(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:
In this case, the index is 148 (the maximum of 148 and 126) and the responsible pollutant is ozone.
13
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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 2 to
calculate the AQI value.
If you have a 24-hour average SO2 concentration greater than or equal to 305 ppb, then use the
breakpoints in Table 2 to calculate the AQI value. If you have a 24-hour value in this range, it will always
result in a higher AQI value than a 1-hour value would.
On rare occasions, you could have a day where the daily max 1-hour concentration is at or above 305
ppb but when you try to use the 24-hour average to calculate the AQI value, you find that the 24-hour
concentration is not above 305 ppb. If this happens, use 200 for the lower and upper AQI breakpoints
(ILo and IHi) in Equation 1 to calculate the AQI value based on the daily max 1-hour value. This
effectively fixes the AQI value at 200 exactly, which ensures that you get the highest possible AQI value
associated with your 1-hour concentration on such days.
What do I do with concentrations for pollutants that have blank places in the table for Breakpoints for
the AQI?
Disregard those numbers. Suppose you had a 1-hour ozone value of 0.104 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:
-(.078-071) +101 = 126
(.085-.071)v J
14
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I. 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.
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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 llpm to 7am).
Previous 8-hour ozone standards
Dav 11
Day
2
12
pm
11 1 7
am
am * 2
3456
3156
Previous ozone standards considered 24 overlapping S-hour averages
The first 8-hour average began at 12am and ended at 7:59 am and the last began at llpm and ended at 6:59 am of the next day,
Because the 8-hour averages for each dav started at 12am, the hours from 12am to 6:59am were "double counted."
This double-counting could result in daily exceedanees on different days influenced by trie same hours.
New (2015) 8-hour ozone standards
Day 12
0 jm
0.1V
1
The new ozone standards eliminate double counting by starting the daily averages at 7am every day.
The first S-hour average begins at 7am and ends at 2:59 pm and the last begins at llpm 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.
Environmental Protection Air Quality Assessment Division EPA-454/B-16-002
Agency Research Triangle Park, NC 27711 May 2016
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