What is the Air Quality Index (AQI)?
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:
of Health Concern
is in this range:
quality conditions are:
by this color:
|0 to 50
|51 to 100
|101 to 150
|151 to 200
|201 to 300
|301 to 500
Each category corresponds to a different level of health
concern. The six levels of health concern and what they mean
- "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
- "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.
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.
Levels of Health Concern
||Air quality is considered
satisfactory, and air pollution poses little or no risk.
||Air quality is acceptable; however,
for some pollutants there may be a moderate health concern for a very
small number of people who are unusually sensitive to air pollution.
||Members of sensitive groups may
experience health effects. The general public is not likely to be
||Everyone may begin to experience
health effects; members of sensitive groups may experience more serious
||Health alert: everyone may
experience more serious health effects.
warnings of emergency conditions. The entire population is more likely
to be affected.
How is AQI Displayed on the New Mexico Environment Department Website?
There are some differences in the official EPA AQI calculation and the method
for calculation and display on the NMED website. The biggest difference is in
the averaging period used. In order to make the AQI for particulate matter be
more responsive during dust storm events, the AQI is calculated for particulate
matter based upon the readings from the last two hours.
The AQI is displayed on the NMED website in a number of ways.
Browsing the map of the state (Maps > New Mexico Map) will show each region as a
colored dot. Those dots are dynamically generated and colored based upon the
worst air quality at any station in that region. Clicking on a region will show
dots for each of the region's stations. In the same manner, the colors of these dots are displayed based upon the AQI
calculated for the most recent data collected at the site. When the mouse hovers
over a dot, the pop up information has an indicator in AQI colors and the text AQI
level ("Good" or "Moderate"), for example. When one of the
regional dots is clicked, the Station Summary Screen is displayed. On that page,
a graphic display in the form of a dial is displayed based upon the AQI as in
this example -
Note that the date, time, index value and pollutant used to calculate the AQI
is displayed on the graphic. If a station measures more than one pollutant that
can be used to calculate AQI, the one that measures the worst air quality is
used as the "responsible" pollutant and is displayed.
Where to get more information
EPA has a number of publications about the AQI. They are available at the