Have you ever been outside on a hot, hazy day and found it harder to breathe? Or maybe you’ve seen an alert on the news about an air quality advisory?

These experiences are both tied to something called the U.S. Air Quality Index (or AQI), which is a tool the Environmental Protection Agency (EPA) uses to communicate information about air quality and health.

About the AQI

The AQI has six color-coded, numerical levels of air quality, ranging from 0 (green) to 500 and higher (maroon). The numbers are tied to the levels of ozone (smog) and particle pollution (exhaust from vehicles, factories and other small particles) in the air. It does not include any measurements about pollen or other allergens.

State and local analysts consult weather forecasts, air monitoring statistics and computer modeling data and then issue AQIs each afternoon for the following day. You can view the AQI for your area by entering your ZIP code at AirNow.

Understanding the AQI Scale

In addition to assigning an index value and color, the AQI forecast may advise certain members of the public to limit or entirely avoid outdoor activities. Affected sensitive groups typically include children, seniors, pregnant individuals, people who have chronic illnesses and those with respiratory diseases, such as asthma.

Here's what the scale means:

• Good (green) – values 0 to 50; no advisories.
• Moderate (yellow) – values 51 to 100; the outside air may be a risk for people sensitive to air pollution.
• Unhealthy for sensitive groups (orange) – values 101 to 150; sensitive groups should avoid prolonged outdoor exposure.
• Unhealthy (red) – values 151 to 200; sensitive groups should avoid outdoor activities, and all others should limit prolonged outdoor exposure.
• Very unhealthy (purple) – values 201 to 300; sensitive groups should avoid all outdoor activities, and all others should limit time outside.
• Hazardous (maroon) – values 301 to 500; everyone should avoid outdoor activities.

Staying Safe

If the AQI is high, the EPA offers several suggestions for reducing your exposure outside and inside your home:

• Choose less intense outside activities (for example, avoid running long distances) and shorten your time outside as much as possible.
• Move outdoor gatherings inside and postpone outdoor chores (like mowing) for another day.
• Exercise away from busy roads where exhaust levels are high.
• Don’t use candles or smoke indoors; limit use of fireplaces and wood-burning stoves.
• Use HEPA air filters in your furnace and air conditioning systems.
• Close your windows and turn on your HVAC system. If you do not have indoor heat or air conditioning and temperatures are at dangerous levels, contact your local government to find a heating or cooling center in your area.

The American Lung Association warns that no one should assume they are safe from health effects because they are “healthy” and not in a sensitive group. If you are outside during an AQI alert, watch for symptoms such as coughing or shortness of breath. Move indoors and seek medical attention, if necessary.

Sources:
AirNow
American Lung Association