Understanding the Air Quality Index (AQI)

Levels of air pollution in parts of Canada and the US have drastically decreased in recent days due to smoke from wildfires spreading across the continent. This has resulted in several states and cities advising their citizens to stay indoors as much as possible in order to avoid the negative impacts of air pollution. However, how do these jurisdictions determine the level of air quality? They do so based on the Air Quality Index (AQI).

The AQI measures five major air pollutants including ozone, particle pollution (known as particulate matter or PM2.5), carbon monoxide, nitrogen dioxide, and sulfur dioxide. The EPA typically releases AQI forecasts for the next day each afternoon. Smoke pollution from wildfires primarily impacts particulate matter which is the primary concern for air quality.

The AQI ranges from zero to 500. A range of 0-50 is considered green, which indicates good air quality and little to no risk of pollution. If the index reaches between 51-100, this is considered a yellow code. Air quality is still acceptable, but there may be some health risks, especially for people who are sensitive to air pollution. Orange and red codes indicate more serious risks of air pollution and are typically associated with greater risks to public health, particularly for sensitive groups including those with heart or lung diseases, adults over 65, pregnant women, children, and those who spend significant time outdoors.

If the AQI reaches between 201-300, the code is purple, which indicates a health alert and an increased risk of negative health effects for everyone. When the AQI exceeds 301, the code is maroon, indicating hazardous air quality and an official health warning of an emergency.

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The EPA recommends reduced outdoor activity during code orange and staying indoors if experiencing symptoms during code red. During code purple, sensitive groups are advised to avoid all outdoor physical activity while others should limit outdoor activities. In areas with maroon codes, everyone should try to stay indoors as smoke particles can lead to burning eyes, runny noses, bronchitis, and other respiratory issues, particularly in people with pre-existing heart or lung diseases. It is recommended to keep the air as clean as possible indoors by avoiding burning candles, using gas stoves or wood fireplaces, and vacuuming (which can stir up particles already inside). Air conditioners should be run with the air intake closed and the filter clean, and masks can be helpful for filtering out particulate matter.

To find out the current AQI levels across the US, Canada, and parts of Central America, visit fire.airnow.gov.

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