What is the Air Quality Index (AQI)?

Higher numbers don't always equate to better results. For example, according to the Air Quality Index, the lower the value, the better.

According to the Air Quality Index (AQI), five major pollutants are responsible for the air's cleanliness: 

1. Surface-level ozone: This is caused by gaseous pollutants being released into the atmosphere by vehicles and these pollutants interact with heat and sunlight. 
2. Particulate matter: These are larger particles that originate from fires, vehicles, power plants, and other sources. 
3. Carbon monoxide (CO): This is caused by the burning of fossil fuels through vehicles and machinery and makes it more difficult for the air to return to a cleaner state.
4. Sulfur dioxide (SO2): This is caused by the burning of sulfur-rich fossil fuels, such as coal and oil, but is also released into the atmosphere by volcanoes and fires.
5. Nitrogen dioxide (NO2): This is caused by the burning of fossil fuels.

Particulate matter and surface-level ozone are more responsible for causing health concerns for people than the other pollutants. The AQI is calculated using national standards for each pollutant set by the U.S. Environmental Protection Agency (EPA).

The AQI is color-coded from green to maroon in increments of 50, except for severe levels, from 0 to 301 and above. When the AQI is indexed from 0 to 50, air quality presents little to no health concerns for the public and is given a green color code. However, when the AQI is indexed from 301 and above, air pollution presents a severe health concern to the public and is given a maroon color code. 

1. Good (0 to 50): Air pollution presents little or no risk. 
2. Moderate (51 to 100): Air pollution presents a slight risk to severely sensitive groups. 
3. Unhealthy for sensitive groups (101 to 150): Air pollution presents a risk to sensitive groups. 
4. Unhealthy (151 to 200): Air pollution presents a risk to all people, but a more severe risk to sensitive groups. 
5. Very Unhealthy (201 to 300): Air pollution presents a severe risk to all people. 
6. Hazardous (301 and above): Air pollution presents a dangerous health warning to all people.

It is important to be aware of the air quality surrounding your area. Densely populated areas are at a higher risk for worse AQI values and pollutants can have long-lasting effects on a person’s health. 


Image: Air pollution by brick factory. (11 March 2019, Janak Bhatta)
Source: AirNow