How do you judge how clean the air outside is?
If you’re like many people, you check to see how clear the sky is, or what the “visibility” is like.
While visibility can tell you something about the levels of certain types of pollutants in the air—namely particulate pollutants—it doesn’t provide a complete picture of air quality. Certain types of pollutants like ozone and carbon monoxide have little effect on visibility; very high concentrations of these gases can be present even on the clearest day.
The U.S. Environmental Protection Agency (U.S. EPA) has created a better indicator of air quality, the Air Quality Index, or AQI. The AQI is calculated based on the levels of five major pollutants in the air: ground-level ozone, particle pollution, carbon monoxide, sulfur dioxide, and nitrogen dioxide. Monitors at more than a thousand locations across the country record the concentrations of these pollutants each day. These measurements are used to calculate AQI values for each of the individual pollutants as well as an overall AQI for the day.
The Air Quality Index runs from 0 to 500: the larger the number, the greater the level of air pollution. To make it easier to use, the index is broken down into six general categories, each category corresponding to a different level of health concern. When the air quality index value is between 101 and 150, for example, air quality is considered to be “unhealthy for sensitive groups”, like people with heart or lung disease; when the value rises to above 200, air quality is considered “very unhealthy” or “hazardous” for the entire population. To check the AQI in your area, visit AirNow.
|
The Air Quality Index |
|
AQI |
Color |
Meaning |
| 0 to 50 | Green | Good |
| 51 to 100 | Yellow | Moderate |
| 101 to 150 | Orange | Unhealthy for sensitive groups* |
| 151 to 200 | Red | Unhealthy |
| 201 to 300 | Purple | Very unhealthy |
| 301 to 500 | Maroon | Hazardous |
*Groups that are unusually sensitive to air pollution include individuals with heart and lung disease, children and older adults.
However, simply knowing what the air quality is like doesn’t protect you against the harmful effects of air pollution. That’s why the U.S. EPA developed a set of step-wise, cautionary statements for each of the individual pollutants (except nitrogen dioxide). The precautions coincide with the six general index categories. For example, when the AQI for ozone rises above 150, active children and adults, and people with lung disease, are cautioned to avoid prolonged or heavy exertion outdoors; when the AQI for sulfur dioxide rises above 300, children and people with heart or lung disease are encouraged to remain indoors. A complete set of recommendations can be found in the U.S. EPA’s publication, Air Quality Index: A Guide to Air Quality and Your Health
