What is AQI?

AQI, or Air Quality Index, is a system for translating sometimes confusing or unintuitive pollutant concentration measurements, into one easy-to-understand scale to clearly represent the health risk posed by ambient air pollution. The index formula usually considers up to 6 main pollutants (PM2.5, PM10, carbon monoxide, sulfur dioxide, nitrogen dioxide and ground level ozone), and calculates the respective health risk (or AQI number) for each one at any given time. The overall AQI number at a given moment is dictated by the "riskiest" pollutant, with the highest AQI number.

The index ranges from 0 to 500, where high index values indicate higher levels of air pollution and higher potential for adverse health effects. Any value larger than 300, for example, is considered to be hazardous, while an AQI value of 0-50, on the other hand, represents good air quality.  

AQI is computed in different ways around the world. China and America have the two most widely used systems. Both are calculated weighting the six key pollutants. The results of these two functions differ only in AQI scores of 200 and below.

Since the American index system yields higher scores for AQI’s under 200, it is thought to be more strenuous. For this reason, the American index has become the general world standard.

**We use the US EPA National Ambient Air Quality Standards to calculate AQI and attribute code color. Both US and Chinese AQI systems are available on the AirVisual app and Node.

The standards are as follows:

 

0-50, “Good”

Air quality is satisfactory and poses little or no health risk. Ventilating your home is recommended.

Recommendations

Enjoy your usual outdoor activities. We recommend opening your windows and ventilating your home to bring in fresh, oxygen-rich air.


51-100, “Moderate”

Air quality is acceptable and poses little health risk. Sensitive groups may experience mild adverse effects and should limit prolonged outdoor exposure.

Recommendations

Enjoy your usual outdoor activities. We recommend opening your windows and ventilating your home to bring in fresh, oxygen-rich air.

 

101-150, “Unhealthy for Sensitive Groups”

Air quality poses increased likelihood of respiratory symptoms in sensitive individuals while the general public might only feel slight irritation. Both groups should reduce their outdoor activity. 

Recommendations

The general public should greatly reduce outdoor exertion. Sensitive groups should avoid all outdoor activity. Everyone should take care to wear a pollution mask. Ventilation is discouraged. Air purifiers should be turned on.

 

151-200, “Unhealthy”

Air quality is deemed unhealthy and may cause increased aggravation of the heart and lungs. Sensitive groups are at high risk to experience adverse health effects of air pollution.

Recommendations

Outdoor exertion, particularly for sensitive groups, should be limited. Everyone should take care to wear a pollution mask. Ventilation is not recommended. Air purifiers should be turned on if indoor air quality is unhealthy.

 

201-300, “Very Unhealthy”

Air quality is deemed unhealthy and may cause increased aggravation of the heart and lungs. Sensitive groups are at high risk to experience adverse health effects of air pollution. 

Recommendations

The general public should greatly reduce outdoor exertion. Sensitive groups should avoid all outdoor activity. Everyone should take care to wear a pollution mask. Ventilation is discouraged. Air purifiers should be turned on.

 

301-500+, “Hazardous”

Air quality is deemed toxic and poses serious risk to the heart and lungs. Everyone should avoid all outdoor exertion.

Recommendations

The general public should avoid outdoor exertion. Everyone should take care to wear a quality pollution mask. Ventilation is discouraged. Homes should be sealed and air purifiers turned on.

 

**Sensitive groups include children, elderly and pregnant people or those suffering from cardiac or pulmonary diseases.


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