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.Ground-level ozone and airborne particles are the two pollutants that pose the greatest threat to human health in this country.
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:
Air Quality Index
(AQI) Values |
Levels of Health Concern |
Colors |
When the AQI
is in this range: |
...air quality conditions are: |
...as symbolized
by this color: |
0 to 50 |
Good |
Green |
51 to 100 |
Moderate |
Yellow |
101 to 150 |
Unhealthy for
Sensitive Groups |
Orange |
151 to 200 |
Unhealthy |
Red |
201 to 300 |
Very Unhealthy |
Purple |
301 to 500 |
Hazardous |
Maroon |
|
Each category corresponds to a different level of health concern. The six levels of health concern and what they mean are:
- "Good" AQI is 0 - 50. Air quality is considered satisfactory, and air pollution poses little or no risk.
- "Moderate" AQI is 51 - 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" AQI is 101 - 150. Although general public is not likely to be affected at this AQI range, people with lung disease, older adults and children are at a greater risk from exposure to ozone, whereas persons with heart and lung disease, older adults and children are at greater risk from the presence of particles in the air.
- "Unhealthy" AQI is 151 - 200. Everyone may begin to experience some adverse health effects, and members of the sensitive groups may experience more serious effects.
- "Very Unhealthy" AQI is 201 - 300. This would trigger a health alert signifying that everyone may experience more serious health effects.
- "Hazardous" AQI greater than 300. This would trigger a health warnings of emergency conditions. The entire population is more likely to be affected.
AQI colors
EPA has assigned a specific color to each AQI category to make it easier for people to understand quickly whether air pollution is reaching unhealthy levels in their communities. For example, the color orange means that conditions are "unhealthy for sensitive groups," while red means that conditions may be "unhealthy for everyone," and so on. |
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