Air Quality Index and Your Health

The AQI is an index for reporting daily air quality, developed by the EPA. It tells citizens how clean or polluted their air is, and what associated health concerns they should be aware of. The AQI focuses on health effects that can happen within a few hours or days after breathing polluted air. The purpose of the AQI is to help citizens understand what local air quality means to their health. To make the AQI as easy to understand as possible, EPA has divided the AQI scale into the different categories shown below.

Air quality is measured by a network of monitors that record the concentrations of the major pollutants at locations throughout the state. These raw measurements are then converted into AQI values using standard formulas developed by EPA. An AQI value is calculated for each of the individual pollutants in an area.

The AQI is based on:

  • ozone levels averaged over an eight-hour period, in parts per billion, and
  • particle pollution levels averaged over a twenty-four hour period, in micrograms per cubic meter.

Find out how you can help!

Air Quality Index Air Quality Descriptor Health Effects Color Code Averaged Values
Ozone Particle Pollution
0-50 Good No Health Notice. No health impacts expected in this range. It’s a great day to be active outside! GREEN 0-54 0-12.0
51-100 Moderate Limited Health Notice. Sensitive people should consider reducing prolonged or heavy exertion. Watch for symptoms such as coughing or shortness of breath. These are signs to take it easy. YELLOW 55-70 12.1-35.4
101-150 Unhealthy for Sensitive Groups Health Notice. People with heart or lung disease, the elderly, teenagers and children should reduce prolonged or heavy exertion. It is okay to be active outside, but take more breaks and do less intense activities. Watch for symptoms such as coughing or shortness of breath. Asthmatics should follow their action plans and keep quick relieve meds handy. Those with heart disease should watch for palpitations, shortness of breath or unusual fatigue and contact your health provider of necessary. ORANGE 71-85 35.5-55.4
151-200 Unhealthy Health Advisory. People with heart or lung disease, the elderly, teenagers and children should avoid prolonged or heavy exertion and consider moving activities indoors or rescheduling. Everyone else should reduce prolonged or heavy exertion. Take more breaks during all outdoor activities. RED 86-105 55.5-150.4
201-300 Very Unhealthy Health Alert. People with respiratory or heart disease, the elderly, teenagers and children should avoid any outdoor activity. Move activities indoors or reschedule to a time when air quality is better. Everyone else should avoid prolonged or heavy exertion. Consider moving activities indoors or rescheduling to a time when air quality is better. PURPLE >105 >150.4

Visit AirNow for more AQI information.

Your Health

Who is most at risk from ozone and particle pollution?

  • Children and Teenagers - Their respiratory systems are still developing and they breathe more per pound of body weight than adults.
  • Individuals with a lung disease - Ozone and particle pollution put additional stress on the lungs in addition to causing various reactions within the lungs. People with existing lung disease have less tolerance for the effects of pollutants.
  • Individuals with heart disease - Particle pollution has long been known to negatively impact heart function but recent studies are also finding a link between ozone and negative impacts on heart function. People with existing heart disease have less tolerance for the effects of pollutants.
  • The Elderly - As people age their bodies have less tolerance for the effects of pollutants.
  • Individuals who are exerting themselves - At higher levels of pollutants even healthy adults who are exerting themselves will bring in more air and thus more pollution into their lungs.
  • New or expectant mothers may also want to take precautions to protect the health of their babies

Sensitive individuals who limit their exposure to poor air quality will reduce the likelihood of the need for additional medication, emergency department visits, and hospitalizations. DEP staff meteorologists remind you to 'Keep an eye on the AQI.'

Smart Exercise

Maine forecasts are issued using an Air Quality Index (AQI). The AQI color codes identify pollution levels and include specific health messages for each category. If you are concerned about your health a good motto is to “Keep an eye on the AQI.”

Although Maine 's bad air days are infrequent, there are still some days when air quality can be a problem for sensitive people. During these days you'll hear warnings to avoid strenuous or prolonged activity outdoors. This does NOT mean that you shouldn't exercise at all, but rather exercise smart.

Smart exercise includes changing the time of day, location and/or the level of your activity, so you won't be exposed to high levels of pollution.

Change the time of the day:

  • Ozone is a photochemical pollutant, which means it needs strong sunlight to form from other pollutants in the air. Ozone can be a problem during the summer months in Maine and peaks during the afternoon and early evening hours. So you could reduce your exposure to high ozone by exercising in the morning.
  • Particle pollution, however, can be high at any time of the day; although it is usually higher in the morning. So avoid exercising during high particle pollution levels by postponing exercise until the afternoon. Particle pollution tends to be higher in the summer and winter, but lower in the spring and fall.

Change your location:

You can protect your health even more by finding a healthier route for your walk or jog - one which avoids busy roads.

Change your activity level:

In addition to changing the time or location of your workout, you could also change the level or duration of activity by walking instead of jogging or reducing the distance of your run on days when air quality is poor.

Remember, to protect your health exercise smart!

Air Quality Forecast Availability

Ground-level ozone concentrations tend to be especially high during the summer months when the weather is hot and sunny. Particle Pollution levels tend to be higher during the Summer & Winter and lower during the Spring & Fall.

DEP staff issue Air Quality Forecasts year-round. The forecast is made available to the public on a daily basis in the following ways:

  • 24-hour toll free Air Quality hotline: 1-800-223-1196
  • Online in this site - daily forecasts
  • EnviroFlash -- Email and text message alert system established by EPA in cooperation with MEDEP.
  • Local Media

General Information about Ozone and Particle Pollution


What is it?

Ozone is an extremely reactive colorless gas comprised of three atoms of oxygen.

In the upper levels of the atmosphere it shields the earth from the sun's harmful ultraviolet rays.

However, ozone close to the ground is a harmful pollutant.

That is why we say, 'Good up high, bad nearby.'

Where does it come from?

Ozone is formed through a complex chemical reaction between volatile organic compounds (VOCs) and nitrogen oxides (NOx) in the presence of sunlight.

Sources of manmade VOCs and NOx include: 1) automobiles, trucks and buses; 2) gasoline storage and transfer; 3) large combustion and industry sources such as utilities; 4) industrial use of solvents and degreasing agents; 5) consumer products such as paints and cleaners; 6) off-road engines such as aircraft, locomotives, boats, construction equipment and lawn and garden equipment.

VOCs are also produced naturally by certain types of vegetation.

Particle Pollution

What is it?

Particle pollution is a term for pollution that includes both solid particles (dust, dirt, soot, smoke, etc.) and liquid droplets found in air. Particles come in a wide range of sizes. Particles less than 10 micrometers in diameter can be inhaled and accumulate in the respiratory system. Particles less than 2.5 micrometers are called 'fine particles'. This is the size range included in the particle pollution forecast. During the winter months in Maine coarse particles (2.5 to 10 micrometers) can be an issue around and downwind of roads and parking lots due to sand and salt being stirred up by winds.

Where does it come from?

Some particles are emitted directly into the air. They come from a variety of sources such as: cars, trucks, buses, locomotives, ships, factories, construction sites, tilled fields, unpaved roads, stone crushing, and the burning of wood.

Other particles form in the air from chemical processes. They are indirectly formed when gases from fuel combustion react with sunlight and water vapor.

Wildfire Smoke

Wildfire smoke can be a problem in Maine from fires in the state, nearby states, Eastern provinces in Canada and even from fires out west.

Smoke from fires contains many different pollutants including carbon monoxide and particle pollution. Particle pollution effects both the lungs and the heart. Therefore, people with respiratory and/or heart disease should take precautions to protect their health.

In slightly to mildly smoky areas individuals suffering from a respiratory disease, children, the elderly and those with heart disease should:

  • Stay indoors with windows and doors closed,
  • Avoid strenuous activity, such as jogging,
  • Avoid using aerosol products such as cleaners, paints and other lung irritants,
  • Use medications as prescribed, and
  • Give yourself a break! Take it easy!

In very smoky areas everyone should follow the precautions listed above to limit their exposure to particle pollution.

When MEDEP Meteorologists are informed of a fire that may be impacting areas within the state, a special statement and/or a forecast update will be issued on the Air Quality Forecast web page ASAP. Depending on the situation, a press release may also be issued.

For fires located within the state the Maine Forest Service, the Maine Emergency Management Agency, the National Weather Service and local emergency personnel will also be involved and working together to protect lives and property.

If you are directed to evacuate please do so and remember to pack all your medications - you don't know how long it will be before you can return. Also, remember to ask for the safest and least smoky escape route they can recommend.

For more information about wildfire health issues and mapping of smoke events check out the links below:

How You Can Help

  • Combine errands, reduce trips
  • Conserve energy - at home, work, everywhere
  • Use environmentally safe paints and cleaning products
  • Conserve electricity and set air conditioners no lower than 78 degrees
  • Choose a cleaner commute - share a ride or use public transportation
  • Avoid using gasoline-powered lawn and garden equipment when unhealthy conditions are forecast
  • Keep car, boat and other engines tuned up according to manufacturer specifications
  • Reduce gas vapors by refueling cars and trucks after dusk
  • Improve gas mileage by inflating tires to recommended pressure
  • Limit idling