www.airnow.gov
Fact S
AIRNow
Air Quality Mapping
Introduction
The U.S. Environmental Protection Agency's (EPA) AIRNow program
collects real-time ground-level ozone data from over 1400 air quality
monitors across the United States and Canada. These data are used
to generate hourly gridded maps that vividly show smog developing
and moving. The gridded data are available free to weather service
providers.
Every year, over 125 million Americans are exposed
to unhealthy levels of smog, primarily ground-level
ozone and particle pollution.
Air quality maps show where air pollution is bad right
now and enables the public to avoid exposure and
alter their behavior when unhealthful air occurs.
Learn more at wnvw.airnow.gov.
New This Year
AIRNow's air quality mapping program is growing:
• More states. New states coming online this year include North Dakota, South Dakota, and Nebraska. This brings the total
states mapping air quality to 46.
• File format. Data are available In GRIB file format.
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 six 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 (wwvv.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
May 1,2005 6:00 pm EOT
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File Format Specifications
Gridded data files are stored in the GRIB (Gridded Binary Data) format. Each file contains a grid that covers the contiguous
United States and contains AQI observations for a given hour. Air quality agencies throughout the United States collect data
each hour during the day and then send it to EPA for processing and quality control at 30 minutes past the hour. These grid
files are available to weather service providers 45 minutes after the data are collected (for example, data collected at 2 p.m.
are available at ~2:45 p.m.). Files only contain data from states and regions participating in the AIRNow program; thus,
some states may be masked ("blanked"). This masking is more evident in the data-sparse western United States. The grid
file specifications follow:
Format: For the hourly AQI files:
US-yymmddhh. grib
where yy=year, mm=month, dd=day, hh=hour in GMT
For the peak AQI files:
US-yymmdd-max. grib
File Contents: Each file contains one hour of gridded observations (or previous day's peak).
File Locations: The grid files are available at the AIRNow Data Management Center's (DMC's) ftp site. Please
contact Alan Chan at 707-665-9900 or e-mail AIRNowDMC@sonomatech.com for details.
Data Specifications: Grid resolution: 8 km (approximate)
Time standard: GMT
Report units: Air Quality Index (AQI). Note that for the GRIB file, parameters and units are listed as
"TOZNE=Total ozone [Dobson]" because ground level ozone with AQI units is not yet included in the
GRIB reference tables.
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
craig@sonomatech.com
alan@sonomatech.com
* Primary Contacts
905101-2190 06/05
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