Smoke from Canadian wildfires has filled skies in the United States, impacting northeastern states in particular, and has left millions of Americans at risk of exposure to poor air quality and health impacts.
As people seek ways to stay safe, it is important to understand how the air quality index, or AQI, works. The color-coded system measures the air quality in relation to certain pollutants and the associated health risks at various levels.
Here is a breakdown of the AQI, the different color codes used and what you should do to protect your health.
What is AQI?
The air quality index, or AQI, measures the air quality and level of health concern it presents as measured by the Environmental Protection Agency.
How does AQI work?
The AQI is measured on a scale of 0 to 500. The higher the AQI values, the greater the level of air pollution and health concern there is, according AirNow.gov. Conversely, the lower the AQI values, the air quality is more satisfactory and the health risks are lower.
The EPA determines the AQI values based on five major air pollutants which are regulated by the Clean Air Act:
- Ground-level ozone
- Particle pollution (also known as particulate matter)
- Carbon monoxide
- Sulfur dioxide
- Nitrogen dioxide
According to the National Weather Service, ground-level ozone and airborne particles present the greatest health threat to humans.
The AQI is measured in six levels:
- 0 to 50
- 51 to 100
- 101 to 150
- 151 to 200
- 201 to 300
- 301 and higher
Each has a different “level of concern” in relation to the air pollutants. It ranges from “good” to “hazardous.” This is based on how someone would be affected after breathing in polluted air for a few hours or days.
Each level is also assigned a corresponding color, with green representing “good” ranging to maroon representing “hazardous.”
If the AQI values are at or are below 100, air quality is generally deemed as satisfactory. However, once the AQI goes above that value, it is unhealthy. This impacts certain sensitive groups of people first, but will affect everyone as the AQI values increase.
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Breaking down AQI values and what they mean
0-50: Code green air is deemed “good.” Air quality is considered satisfactory, and air pollutants pose little to no risk for human health.
51-100: Code yellow air is considered “moderate.” While this air quality is still regarded as “acceptable,” some people may begin to experience health impacts, especially those who are sensitive to air pollution.
101-150: Once the air quality reaches code orange, it has become unhealthy. This color means concern has reached “unhealthy for sensitive groups.” Those who are considered sensitive include those with lung diseases, those who have asthma, older people, children, teenagers and those who are active outdoors, according to the NWS.
151-200: When the air quality reaches code red, it is “unhealthy” for everyone. The general public may begin to experience health impacts, while those in sensitive groups will have more serious health effects.
201-300: Code purple is considered “very unhealthy” Health alerts are generally issued during this color, and the health risk has increased for everyone.
300+: The last is code maroon and is considered “hazardous.” This will usually prompt a health warning, and everyone is likely to be affected.
What is a red flag warning?Here’s what you can do if your state is under alert.
What should you do for each AQI level?
During code green, you are OK to be active outside.
During code yellow, sensitive groups should consider reducing their time spent outside and should monitor health impacts, such as shortness of breath or coughing. Others are good to go outdoors.
During code orange, sensitive groups should reduce their outdoor exposure and continue to watch for their health.
During code red, sensitive groups should avoid outdoor exposure and everyone else should reduce prolonged time outdoors.
During code purple and code maroon, everyone should avoid outdoor activities.
US air quality index map
You can view the latest wildfire and smoke data and its impact on air quality in our database.
