What is the Air Quality Index (AQI)?

The Air Quality Index (AQI) is a standardized system used by government agencies to communicate to the public how polluted the air currently is or how polluted it is forecast to become. As the AQI increases, an increasingly large percentage of the population is likely to experience severe adverse health effects. Different countries have their own indices, but the most widely recognized is the US EPA (Environmental Protection Agency) standard, which our calculator utilizes.

How the AQI Calculator Works

This calculator computes the air quality based on the concentrations of several ground-level pollutants, including Particulate Matter (PM2.5 and PM10), Ozone (O3), Nitrogen Dioxide (NO2), Carbon Monoxide (CO), and Sulfur Dioxide (SO2). The formula works by finding the individual index for each pollutant and then defining the overall AQI as the highest value among them. This "worst-case" approach ensures that public health warnings are triggered even if only one pollutant is at a dangerous level.

Understanding the AQI Levels

The index ranges from 0 to 500. Here is how to interpret the results:

• 0 - 50 (Good): Air quality is considered satisfactory, and air pollution poses little or no risk.
• 51 - 100 (Moderate): Air quality is acceptable; however, for some pollutants, there may be a moderate health concern for a very small number of people.
• 101 - 150 (Unhealthy for Sensitive Groups): Members of sensitive groups may experience health effects. The general public is not likely to be affected.
• 151 - 200 (Unhealthy): Everyone may begin to experience health effects; members of sensitive groups may experience more serious health effects.
• 201 - 300 (Very Unhealthy): Health alert: everyone may experience more serious health effects.
• 301+ (Hazardous): Health warnings of emergency conditions. The entire population is more likely to be affected.

Frequently Asked Questions

What is the difference between PM2.5 and PM10? PM2.5 refers to fine particles with a diameter of 2.5 micrometers or less, while PM10 includes particles up to 10 micrometers. PM2.5 is generally considered more dangerous because it can travel deeper into the lungs and even enter the bloodstream.

When should I wear a mask? Health experts usually recommend wearing an N95 or higher-rated mask when the AQI exceeds 150 (Unhealthy), especially for those spending extended periods outdoors or those with underlying respiratory conditions.