What you need to know about the
Air Quality Index (AQI)
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The Environmental Protection Agency (EPA) recently revised its
method of reporting air quality
and the associated health effects. The Air
Quality Index (AQI) replaces the Pollutant Standards
Index (PSI) we previously used to report air quality to the public.
- What the numbers mean - The AQI is a measure of air quality based
on a percentage of the federal air quality standard: an AQI of 100 means the pollutant level
is equal to the federal standard for that
pollutant. An AQI below 100 means the air quality is better than
the standard, and above 100 can
be considered unhealthful. The higher the number, the more air
pollution we are breathing.
In Santa Barbara County, we report the AQI for ozone,
based on the federal 8-hour standard. Ozone is the only
pollutant for which we have recently violated a federal air quality
standard.
The EPA specifies the colors to be used to report
the AQI, based on the numbers and their health-related categories. To
view these categories and colors, see What Does
the AQI Look Like below.
- "Today's AQI" is calculated based on
ozone levels averaged over 8 hours, beginning at
8 a.m. For this reason, short periods of high ozone levels may not be
reflected. "Yesterday's AQI," also available on the daily
AQI page, reports the highest 8-hour average from the
previous day.
"Yesterday's AQI" is an important
indicator of the expected air quality for today, so long as the
weather patterns continue.
If you are in a category of people sensitive to air pollution, you
should use today's and yesterday's AQI in conjunction with the
Station
Data, which are updated hourly and also change colors when
standards are violated. If you need help understanding the correlation
between AQI and actual ozone levels, call us, (805) 961-8800, or
e-mail us at apcd@sbcapcd.org.
- Comparing the AQI to the PSI - If you are accustomed to using the PSI, there are several important
differences.
First, the AQI is based on an 8-hour average, while the PSI was based
on a 1-hour average.
Second, the AQI has broken the numbers into new
health-related categories and cautionary statements:
From 51 - 100, which is still better than the
federal 8-hour standard, there is a new statement, "Unusually
sensitive people should consider limiting prolonged outdoor
exertion."
Previously, PSI values from 101 - 200 were called "unhealthful." The
AQI establishes new categories, from 101 -150, "unhealthy for
sensitive groups," and from 151 - 200, "unhealthy," and adds a corresponding
statement indicating which specific groups in the
population are most at risk for that pollutant. For example, when the AQI is
between 101 and 150 for ozone, the AQI
report will contain the statement: "Active children and adults, and people
with respiratory disease, such as asthma, should limit prolonged
outdoor exertion."
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AQI
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Health
Categories
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Ozone
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201
to 300
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Very
Unhealthy
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Active
children and adults, and people with respiratory disease,
such as asthma, should avoid all outdoor exertion; everyone
else, especially children should limit outdoor exertion.
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151
to 200
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Unhealthy
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Active
children and adults, and people with respiratory disease,
such as asthma, should avoid prolonged outdoor exertion;
everyone else, especially children should limit prolonged
outdoor exertion.
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101
to 150
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Unhealthy
For Sensitive Groups
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Active
children and adults, and people with respiratory disease,
such as asthma, should limit prolonged outdoor exertion.
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51
to 100
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Moderate
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Unusually
sensitive people should consider limiting prolonged outdoor
exertion.
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0
to 50
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Good
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None
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For more information about the AQI, you may download the EPA's
brochure, Air Quality Index - A guide to air
quality and your health. This brochure is in Adobe Acrobat pdf
format. For downloading instructions see How
to View and Download Documents.
See Today's AQI
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