What is the Air Quality Index, what does it mean and what does it measure?

Record dangerous air quality levels continued in parts of the eastern U.S. on Thursday as smoke from Canadian wildfires continues to flow across the border.

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The National Weather Service is warning residents in New York City, Boston, Philadelphia and Washington, D.C., that unhealthy air quality levels will continue through the day and likely into the weekend.

What do unhealthy air quality indexes mean, and how are they measured?

Here’s what we know now.

What is the Air Quality Index?

The Air Quality Index (AQI) is a measure of the number of pollutants in the air in a specific area.

The index moves up and down as pollutants in the air change.

How does the AQI work?

The AQI has a range of from 0 to 500.  The higher the AQI value, the greater the level of air pollution.

AQI values at or below 100 are generally thought of as acceptable, with an index under 50 being considered “satisfactory,” with no risk to human health.

An AQI value above 100 is considered unhealthy.

The AQI is divided into six categories with each category corresponding to a different level of health concern from “Good” to “Hazardous.”

What does the AQI measure?

The AQI tracks five major air pollutants:

· Ground-level ozone

· Carbon monoxide

· Sulfur dioxide

· Nitrogen dioxide

· Airborne particles, or aerosols

According to Air Now, ground-level ozone and airborne particles are the two air pollutants that pose the greatest risk to human health.

How is the information collected?

Both satellites and instruments on the ground gather information about what we are breathing.

When it comes to the situation in the Eastern United States now, the Joint Polar Satellite System (JPSS) collects information about smoke particles from wildfires.

When is air quality bad enough that you should stay inside?

When the AQI goes up, the risk to human health increases as well. Below are the levels of the AQI and what they mean.

  • Good – 0 to 50 – Air quality is considered satisfactory and air pollution poses little or no risk to health.
  • Moderate – 51 to 100 – Air quality is acceptable. However, there may be a risk for some people, particularly those who are unusually sensitive to air pollution.
  • Unhealthy for sensitive groups – 101 to 150 – Members of sensitive groups may experience health effects. The general public is less likely to be affected.
  • Unhealthy – 151 to 200 – Some members of the general public may experience health effects; members of sensitive groups may experience more serious health effects.
  • Very unhealthy – 201 to 300 – Health alert: The risk of health effects is increased for everyone.
  • Hazardous – 301 and above – Health warning of emergency conditions: everyone is more likely to be affected.
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