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The Air
Quality Index
The AQI is an index for reporting daily
air quality. It tells you how clean or polluted your air
is, and what associated health effects might be a concern
for you. The AQI focuses on health effects you may experience
within a few hours or days after breathing polluted air.
EPA calculates the AQI for five major air pollutants regulated
by the Clean Air Act: ground-level ozone, particle pollution
(also known as particulate matter), carbon monoxide, sulfur
dioxide, and nitrogen dioxide. For each of these pollutants,
EPA has established national air quality standards to
protect public health.
How Does the AQI Work?
Think of the AQI as a yardstick that runs
from 0 to 500. The higher the AQI value, the greater the
level of air pollution and the greater the health concern.
For example, an AQI value of 50 represents good air quality
with little potential to affect public health, while an
AQI value over 300 represents hazardous air quality.
An AQI value of 100 generally corresponds to the national
air quality standard for the pollutant, which is the level
EPA has set to protect public health. AQI values below
100 are generally thought of as satisfactory. When AQI
values are above 100, air quality is considered to be
unhealthy-at first for certain sensitive groups of people,
then for everyone as AQI values get higher.
Understanding the AQI
The purpose of the AQI is to help you understand
what local air quality means to your health. To make it
easier to understand, the AQI is divided into six categories.
Each category corresponds to a different level of health
concern. The levels of health concern and what they mean
are:
"Good" The
AQI value for your community is between 0 and 50. Air
quality is considered satisfactory, and air pollution
poses little or no risk.
"Moderate" The
AQI for your community is between 51 and 100. Air quality
is acceptable; however, for some pollutants there may
be a moderate health concern for a very small number of
people. For example, people who are unusually sensitive
to ozone may experience respiratory symptoms.
"Unhealthy for Sensitive Groups"
When AQI values are between 101 and 150,
members of sensitive groups may experience health effects.
This means they are likely to be affected at lower levels
than the general public. For example, people with lung
disease are at greater risk from exposure to ozone, while
people with either lung disease or heart disease are at
greater risk from exposure to particle pollution. The
general public is not likely to be affected when the AQI
is in this range.
"Unhealthy" Everyone
may begin to experience health effects when AQI values
are between 151 and 200. Members of sensitive groups may
experience more serious health effects.
"Very Unhealthy" AQI
values between 201 and 300 trigger a health alert, meaning
everyone may experience more serious health effects.
"Hazardous" AQI
values over 300 trigger health warnings of emergency conditions.
The entire population is more likely to be affected.
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