www.airnow.gov
Introduction
Fact Sheet
Air Quality Forecasts
and Observations
The U.S. Environmental Protection Agency's (EPA) AIRNow program collects
city-specific smog observations and forecasts from state and local air quality
agencies across the United States and Canada that issue air quality forecasts,
alerts, and action days. These data provide three types of information:
1.	Air quality forecasts. Similar to maximum temperature forecasts, air quality
forecasts represent the maximum smog levels expected for the current day, next
day, and beyond. These forecasts are issued by meteorologists in each state,
collected by the AIRNow program, and distributed freely to weather service
providers.
2.	Current air quality conditions. Like current temperature, the current air
quality values provide the highest Air Quality Index (AQI) reading observed in
each city.
3.	Previous day's AQI maximum. Similar to yesterday's maximum
temperature, this data value provides the peak AQI reached at any monitor in
each city on the previous day.
Every year, over 125 million Americans are exposed
to unhealthy levels of smog, primarily ground-level
ozone and particle pollution.
Air quality forecasts and current conditions enable
the public to avoid exposure and alter their behavior
before unhealthy air occurs. Sensitive individuals
(e.g., people with asthma, the elderly, and children)
can use this information to reduce or avoid adverse
health effects.
Learn more at ti'tiw. airiiow.gov.
New This Year
AIRNow's air quality forecasting program is expanding:
•	More cities and forecasts. Close to 300 cities across the United States currently forecast air quality during part of the year; even more
cities forecast year-round.
•	Quicker delivery. AIRNow's Data Management Center (DMC) updates forecast files at 5, 15, and 35 minutes past the hour.
About the Air Quality Index
The EPA developed the Air Quality Index (AQI) which reports levels of
ozone, particle pollution, and other common air pollutants on the same
scale. An AQI reading of 101 corresponds to a level that is above the
national air quality standard—the higher the AQI rating, the greater the
health impact.
The AQI is divided into color-coded categories, and each category is
identified by a simple informative descriptor. The descriptors are
intended to convey to the public information about how air quality within
each category relates to public health. The table below defines the AQI
categories.
AQI and Health Effects Resources:
About the AQI (www.airnow.gov/aqi_cl.pdf)
Air Quality Guide for Ozone (www.airnow.gov/aqguide.pdf)
Air Quality Guide for Particle Pollution
(www.airnow.gov/airqualityguideparticles.pdf)
Smog: Who Does It Hurt?
(www.airnow.gov/health/smog.pdf)
Ozone and Your Health (www.airnow.gov/ozone-c.pdf)
Particle Pollution and Your Health
(www.airnow.gov/particle/pm-color.pdf)
AQI Numbers
AQI Category
(Descriptor)
AQI Color
Color Formulas
(RGB) (CMYK)
0-50
Good
Green
0,228,0
224,0,224,30
51 - 100
Moderate
Yellow
255,255,0
0,0,255,0
101 - 150
Unhealthy for Sensitive Groups
Orange
255,126,0
0,132,255,0
151 -200
Unhealthy
Red
255,0,0
0,255,255,0
201 - 300
Very Unhealthy
Purple
153,0,76
0,153,80,102
301 - 500
Hazardous
Maroon
76,0,38
0,76,38,179

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File Format Specifications
Data are stored in an ASCII file, which contains yesterday's observed maximum AQI and the latest forecasts and observations
for all cities. Air quality agencies throughout the United States typically issue these forecasts once or twice a day. Agencies
usually submit the forecasts in the late morning to early afternoon hours (local time) with all forecasts completed by 1700 ET
(2100 UTC) each day. Current observations are updated each hour. The data file is updated at 5, 15, and 35 minutes past the
hour. File specifications are as follows:
Format:	forecast.csv
File Contents: The file contains forecasts for the current and next day. For some cities, the file contains forecasts for
two to five days. It also contains the current observations for each city and the previous day's maximum
AQI readings.
Location of File: The file is available at the AIRNow Data Management Center's ftp site. Please contact Alan Chan at 707-
665-9900 or e-mail AIRNowDMC@sonomatech.com for details.
Field Delimiter: | (ASCII character 124)
Report Units: Air Quality Index
Issue date|Valid date|Valid time|Time zone|Record sequence|Data type|Primary|City name|State code|Latitude|Longitude|Pollutant|AQI value|AQI category|Action day|Discussion|
Issue date|Valid date|Valid time|Time zone|Record sequence|Data type|Primary|City name|State code|Latitude|Longitude|Pollutant|AQI value|AQI category|Action day|Discussion|
Issue date|Valid date|Valid time|Time zone|Record sequence|Data type|Primary|City name|State code|Latitude|Longitude|Pollutant|AQI value|AQI category|Action day|Discussion|
Issue date|Valid date|Valid time|Time zone|Record sequence|Data type|Primary|City name|State code|Latitude|Longitude|Pollutant|AQI value|AQI category|Action day|Discussion|
For Data Field Definitions, see the table on the next page.
Example Records:
05/01/05|05/01/05|17:00|EDT|0|0|Y|Columbus|OH|39.9890|-82.9870|PM2.5|49|Good|No||
05/01/05|05/01/05|17:00|EDT|0|0|N|Columbus|OH|39.9890|-82.9870|C)ZC>NE|33|Good|No||
05/01/05|04/30/05||EDT|-1 |Y|Y|Columbus|OH|39.9890|-82.9870|PM2.5|70|Moderate|No|An upper-level trough
05/01 /05|04/30/05||EDT|-1|Y|N|Columbus|OH|39.9890|-82.9870|OZONE|35|Good|No|An upper-level trough...
05/01 /05|04/30/05||EDT|-1 |Y|N|Columbus|OH|39.9890|-82.9870|PM10|17|Good|No|An upper-level trough...
05/01 /05|05/01/05||EDT|0|F|Y|Columbus|OH|39.9890|-82.9870|PM2.5|49|Good|No|An upper-level trough...
05/01 /05|05/01/05||EDT|0|F|N|Columbus|OH|39.9890|-82.9870|OZC>NE|33|Good|No|An upper-level trough...
05/01 /05|05/02/05||EDT| 1 |F|Y|Columbus|OH|39.9890|-82.9870|PM2.5|42|Good|No|An upper-level trough...
05/01 /05|05/02/05||EDT|1|F|N|Columbus|OH|39.9890|-82.9870|OZONE|35|Good|No|An upper-level trough...
05/01/05|05/03/05||EDT|2|F|Y|Columbus|OH|39.9890|-82.9870|PM2.5||Moderate|No|An upper-level trough...

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Data Field Definitions
Field Name
Length
Units/Format
Description
Sample
Issue date
8
mm/dd/yy
Local date that forecast is issued. Note that for current and
yesterday's AQI, this field is always today's date.
05/01/05
Valid date
8
mm/dd/yy
Local date that forecast is valid for or local date that an
observation is made.
05/01/05
Valid time 1
5
hh:mm
Time that a record is valid. Note that for forecasts and
yesterday's AQI, this field will be blank.
17:00
Time zone
3
Text
Time zone for report observations. Note that for forecasts
and yesterday's AQI, this field will be blank.
EDT
Record
sequence
3
Numeric
Indicates day number of a forecast or whether it is an
observation. For example,
-1 - Yesterday's observed maximum AQI
0	- Same-day forecast or hourly AQI observation
1	- Next-day forecast
Note that this is not always correct for forecasts. Always
refer to the "Valid date" field to determine when a forecast is
valid for.
-1
Data type
1
Text
F - Forecast
Y - Yesterday's AQI
O - Hourly AQI Observation
O
Primary 2
1
Text
Y - primary pollutant (i.e., highest AQI reading)
N - not primary
N
City name
45
Text
City
Columbus
State code
2
Text
State
OH
Latitude
7
Numeric
Latitude of a city (decimal degrees)
39.9890
Longitude
9
Numeric
Longitude of a city (decimal degrees)
-82.9870
Pollutant
20
Text
Pollutant:
OZONE = Ozone
PM10 = Coarse Particles (10 |jm)
PM2.5 = Fine Particles (2.5 |jm)
CO = Carbon monoxide
N02 = Nitrogen dioxide
S02 = Sulfur dioxide
OZONE
AQI value 3
3
Numeric
0 to 500
33
AQI category
40
Text
Good
Moderate
Unhealthy for Sensitive Groups
Unhealthy
Very Unhealthy
Hazardous
Good
Action Day
3
Yes/No
Air quality action day
Yes
Discussion
4000
Text
Forecast discussion. Note that for hourly AQI observations
and cities without forecast discussions, this field will be
blank.
An upper-level
trough...
1	Valid time is blank for forecasts and previous day's AQI.
2	Primary indicates that different pollutant forecasts for the same city on the same day exist. This field indicates whether a given forecast is for the
primary pollutant (i.e., maximum AQI) for that day. This should be N for all but one record for a given city and day.
3	AQI value is blank for cities with only AQI categorical forecasts.

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Guidelines for the Use of AIRNow Data. Forecasts, and
Advisories
•	Credit should be given to the appropriate source, either EPA AIRNow or a state/local
air quality agency, if known.
•	Air quality data, forecast values, and advisory statements should not be altered in any
way and should be disseminated as received.
•	Air quality observed and forecast values should be disseminated in accordance with
the Air Quality Index (AQI) and corresponding RGB colors as follows:
AQI Level
Color
R
G
B
Good
Green
0
228
0
Moderate
Yellow
255
255
0
Unhealthy for Sensitive Groups
Orange
255
126
0
Unhealthy
Red
255
0
0
Very Unhealthy
Purple
153
0
76
Hazardous
Maroon
76
0
38
•	All end users who receive these data should be updated with the most current data
available when possible, and, in particular, when advisories are issued by the
state/local air quality agencies. The AIRNow program updates all data hourly.
•	AIRNow observational data are not fully verified or validated and should be considered
preliminary. As such, they should not be used to formulate or support regulation,
guidance, or any other government or public decision.
•	Questions regarding AIRNow data, forecasts, and advisories should be directed to
AIRNowDMC@sonomatech.com and white.iohne@epa.gov.
Contacts
U.S. Environmental Protection Agency
* Chet Wayland, Project Manager
John White, AIRNow Contract Officer
Susan Stone, Health Effects
Phone
(919) 541-4603
(919) 541-2306
(919) 541-1146
E-mail
wayland.richard@epa.gov
white.johne@epa.gov
stone.susan@epa.gov
Data Management Center - Sonoma Technology, Inc.
Tim Dye, Program Manager
Craig Anderson, DMC Manager
*Alan Chan, DMC Lead
Sonoma Technology,Inc.
Phone
(707) 665-9900
(707) 665-9900
(707) 665-9900
E-mail
tim@sonomatech .com
era ig @so n o mate ch. co m
alan@sonomatech.com
* Primary Contacts
905101-2190 06/05

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