Air Quality Index Color Code Guide

Air Quality Index Color Code Guide

Air Quality

Weather Conditions

Recommended Actions

Health Effects


AQI: 0-50

  • Cool summer temperatures
  • Windy conditions
  • Significant cloud cover
  • Heavy or steady precipitation
  • Keep cars and boats tuned up
  • Use environmentally safe paints and cleaning products
  • Conserve electricity-set A/C to highest comfortable level
  • No health effects are expected.


AQI: 51-100

  • Temperatures in the upper 70's to lower 80's
  • Light to moderate winds
  • Partly cloudy or mostly sunny skies
  • Chance of rain or afternoon thunderstorms
  • Keep cars and boats tuned up
  • Use environmentally safe paints and cleaning products
  • Conserve electricity-set A/C to highest comfortable level
  • Unusually sensitive people should consider limiting prolonged outdoor exertion.

Unhealthy for Sensitive Groups

AQI: 101-150

  • Temperatures in the 80's and 90's
  • Light winds
  • Mostly sunny skies
  • Slight chance of afternoon thunderstorms
  • Limit daytime driving
  • Limit vehicle idling
  • Refuel vehicles after dusk
  • Don't "top off" your gas tank
  • Avoid congested periods
  • Use water-based paints
  • Use transit or car pool
  • Bike or walk for short trips
  • Use newest/best maintained car
  • Combine trips and share rides
  • Postpone using gasoline mowers
  • Barbecue without starter fluid
  • Active children and adults, and people with respiratory disease, such as asthma, should limit prolonged outdoor exertion.


AQI: 151-200

  • Hot, hazy, and humid
  • Stagnant air
  • Sunny skies
  • Little chance of precipitation
  • 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.

Very Unhealthy

AQI: 201-300

  • Hot and very hazy
  • Extremely stagnant air
  • Sunny skies
  • No precipitation
  • Active children and adults, and people with respiratory disease such as asthma, should avoid all outdoor exertion; everyone else, especially children, should avoid prolonged outdoor exertion.

AQI refers to the Air Quality Index. An AQI of 100 is equivalent to the National Ambient Air Quality Standard (NAAQS).
An AQI greater than 100 is considered to be above the national standard or NAAQS.
AQI Calculation Table is available online to convert raw ozone concentrations to the Air Quality Index.

The weather conditions listed above are common weather types associated with the respective air quality levels.
A combination of part or of all these weather conditions could lead to a certain level of observed air quality.

The Air Quality Index and Your Health

You’ve probably heard the words “code red” air quality, especially if you live in or near an urban area.  Knowing what the color codes mean can help you protect your health and the health of your loved ones. 

The color-coded Air Quality Index (AQI) describes air quality levels in a standard way all across the country.  In other words “code red," means the same thing in Los Angeles as it does in Raleigh, NC or Washington, D.C.

Each color corresponds to a different level of health concern.  Below are the color codes, from best to worst, with their corresponding health warnings.


Level of Health Concern

AQI Values



0 to 50



51 to 100


Unhealthy for sensitive groups

101 to 150



151 to 200


Very Unhealthy

201 to 300



301 to 500

As you can see, each color also corresponds to a range of Air Quality Index Values.  You can 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 danger.  For example, an AQI value of 50 represents "good" air quality and little danger to public health, while an AQI value of 250 represents "very unhealthy" air quality. 

The most important number on the scale is 100, because 100 corresponds to the National Ambient Air Quality Standard (NAAQS), which is set by the U.S. Environmental Protection Agency (EPA) to protect public health.  So, AQI values below 100 are generally thought to be satisfactory.  When AQI values rise above 100, air quality is considered unhealthy – at first for certain sensitive people, then for everyone as AQI values get higher.

The AQI is most commonly used to describe ground-level ozone levels*.  However, the AQI can be used to represent five pollutants that pose a threat to human health.  These pollutants are:

  • Ground-level Ozone or O3
  • Particulate Matter (soot and dust) or PM
  • Carbon Monoxide or CO
  • Sulfur Dioxide or SO2 and
  • Nitrogen Dioxide or NO2

The EPA sets national standards for these five pollutants under the Clean Air Act.  The EPA and other researchers have studied the health effects of different levels of these pollutants to determine where to set the standards and health warnings.

For each pollutant, a color code represents a specific range of concentrations.  For ground-level ozone, for example, the yellow level includes a concentration range of 0.065 to 0.084 parts per million (ppm).  For carbon monoxide, the yellow range represents a concentration range of 4.5 to 9.4 ppm.  For both pollutants, the color yellow poses a “moderate” level of health concern.  And for both pollutants the upper end of this range (0.84 ppm for ozone, 9.4 ppm for carbon monoxide) is the national standard set by the EPA, so the upper end of both ranges is equal to an AQI value of 100.  As you can see, the Air Quality Index provides a common reference for standardizing the five pollutants in relation to their health impacts.

Air quality agencies measure all five pollutants with a monitor network nationwide.  For major metropolitan areas, the measurements are converted to AQI values, and the pollutant with the highest AQI is reported daily.  In North Carolina, you can hear daily AQI reports by calling 1-888-AIRWISE (1-888- 247-9473).  In the Charlotte area, call (704) 333-7664. 

Many state and local air quality agencies also issue air quality forecasts using the AQI color code.  You may have seen these forecasts on the evening news or in the newspaper in your area.  By paying attention to these forecasts, you can protect your health by adjusting your activities on days predicted to have poor air quality. 

For nationwide ozone mapping and ozone forecasts, visit US EPA AIRNOW at

For more information on ground-level ozone in North Carolina, visit the NC Ozone Forecast Center at .

To learn more about the Air Quality Index and all five pollutants, visit .

* What is ground-level ozone?  First of all, it’s not the same thing as the “ozone layer” or the “hole in the ozone"!  Ozone occurs naturally in the upper atmosphere and protects us from the sun’s ultraviolet radiation.  This “ozone layer” is becoming thinner, especially in the Polar Regions.  However, “ozone pollution” or “ground-level ozone” occurs in the lower atmosphere, where we live and breathe.  It’s created when various man-made pollutants combine in the heat of the sun.  Because heat and strong sunlight are necessary for ground-level ozone formation, ozone is generally a summertime problem.  Small amounts of ozone do occur naturally because of emissions from forest fires and even from trees.  However, most ground-level ozone is produced by human activities.  Ground-level ozone can damage lung tissues and the leaves of plants.    Remember - - ozone is “good up high, bad nearby”!