2024 update to the United States Air Quality Index (U.S. AQI)
Summary
On May 6, 2024, the U.S. Environmental Protection Agency (EPA) implemented an update to the United States Air Quality Index (U.S. AQI), the EPA’s color-coded tool for communicating air quality conditions to the public. The new U.S. AQI lowers the concentration threshold at which fine particulate matter (PM2.5) is considered “good” from 12 µg/m3 to 9 µg/m3 and lowers the PM2.5 thresholds, often referred to as “breakpoints”, for the “Very Unhealthy” and “Hazardous” categories. The EPA’s decision acknowledges new research indicating health risks even at low PM2.5 levels.
This article provides additional context and details regarding this change and IQAir’s implementation of this change across its various air quality products.
What is the United States Air Quality Index (U.S. AQI)?
The U.S. AQI is an air quality tool developed by the United States Environmental Protection Agency (EPA) to communicate to the public health risk due to outdoor air pollution. Its goal is to simplify and distill complicated air quality data into useful, easy to understand information regarding the health risks pose by current or future air quality conditions. While globally there are over 30 different AQIs, the U.S. AQI is widely recognized the most influential. The U.S. implemented the world’s first air quality index in 1976 to draw public attention to the issue of air pollution.
The purpose of the U.S. AQI is to quantify the level of air pollution at a certain location from different measured concentrations of air pollutants as one single number between 0 and 500, and to classify it as one out of six color-coded categories (Good, Moderate, Unhealthy for Sensitive Groups, Unhealthy, Very Unhealthy, Hazardous) which are each associated with different health risk warnings.
The U.S. AQI is calculated by measuring concentrations of up to six pollutants, that are referred to as criteria pollutants, consisting of fine particulate matter (PM2.5), coarse particulate matter (PM10), ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2) and carbon monoxide (CO) at a specific location. Each pollutant's concentration is converted into an index number; the highest of these determines the AQI at this location. The pollutant with the highest number is termed the dominant pollutant. In most places and at most times, the dominant pollutant is PM2.5, fine particles of up to 2.5 microns diameter. These particles can penetrate deep into our lungs or bloodstream and pose health risks. They include particles from smoke and soot in addition to fine dust.
How is the U.S. AQI changing?
On 6th May 2024, the U.S. Environmental Protection Agency (EPA) implemented an update to the United States Air Quality Index (U.S. AQI), the EPA’s color-coded tool for communicating air quality to the public. The new U.S. AQI lowers the concentration threshold at which fine particulate matter (PM2.5) is considered “good” from 12 µg/m3 to 9 µg/m3 and lowers the PM2.5 thresholds, often referred to as "breakpoints", for the “Very Unhealthy” and “Hazardous” categories. The EPA decision acknowledges new research indicating health risks even at low PM2.5 levels. As a consequence of this change, U.S. AQI values and the associated colors could in more instances go from predominantly “green” values to more “yellow” values.
The following table shows the U.S. AQI and the new and old PM2.5 breakpoints:
The following graph provides examples how the new and old PM2.5 breakpoints can lead to recategorization of the same PM2.5 concentration in terms of U.S. AQI:
How is IQAir reacting to this change?
As of May 6, 2024, the EPA has updated its U.S AQI PM2.5 breakpoints. IQAir has begun implementing the updated breakpoints across all IQAir products on the same day, with the goal of syncronizing the change with that of the EPA.
The implementation and changes for IQAir products are as follows:
As of May 6, 2024, all U.S. AQI values on the mobile IQAir AirVisual app have been updated to correspond to the new PM2.5 breakpoints and health recommendations. This applies to air quality data that is displayed in the AirVisual app for IQAir air quality monitors and air purifiers, as well as air quality data for published stations and cities, including the air quality map. The updated U.S. AQI will also have been applied to the IQAir major city ranking in the app.
Below is an example of how AQI numbers and colors change for the same measured PM2.5 concentration under the old and new U.S. AQI.
On May 6, 2024, IQAir has started to automatically roll out a firmware update that applies the new U.S. AQI to your AirVisual Pro device display. Your AirVisual Pro must be connected to the internet for the firmware update to take effect. If your AirVisual Pro hasn’t been updated, you may observe mismatches between the U.S. AQI numbers and colors shown on your device and those shown in the IQAir AirVisual app and map, as well as on the IQAir website and in the dashboard.
On May 6, 2024, IQAir has started to automatically roll out a firmeware update that applies the new U.S. AQI to your Atem X. Your Atem X must be connected to the internet for the firmware update to take effect. If your Atem X hasn’t been updated, you may observe mismatches between the U.S. AQI numbers and colors shown on your device and those shown in the IQAir AirVisual app and map, as well as on the IQAir website and in the dashboard.
On May 6, 2024, all U.S. AQI values have been updated to correspond to the new PM2.5 breakpoints and health recommendations. This applies to all U.S. AQI values displayed in the dashboard, to all downloadable device and device groups data, and to all city and station widgets. Note that the updated U.S. AQI also applies to device historical data downloads.
IQAir website: air quality pages and map
On May 6, 2024, all U.S. AQI values have been updated to correspond to the new PM2.5 breakpoints and health recommendations on the IQAir map, on the station, city, state and country pages, as well as the live major city ranking.
Below is another example, how AQI numbers and colors change for the same measured PM2.5 concentration under the existing and new AQI:
Please note, that while PM2.5 is the most measured pollutant and determines the U.S. AQI in most locations for most of the time, there can be other pollutants that determine U.S. AQI. The EPA has not changed the breakpoints for these other pollutants. Also, the changes to the U.S. AQI do not affect you if you have set up your devices to follow the Chinese AQI (CN AQI) which is less stringent than the U.S. AQI.
U.S. AQI⁺ on IQAir
While IQAir has always used hourly averages for pollutant data, from October 2024, we are now explicitly indicating this in our user interface by labeling it as U.S. AQI⁺. This distinguishes IQAir’s real-time, hourly aggregated air quality data from other AQI systems that may use different averaging periods, such as the 24-hour averages commonly applied in traditional U.S. AQI calculations. By highlighting U.S. AQI⁺, IQAir ensures that users understand they are viewing the most current air quality information, which can differ from AQI systems that rely on longer averaging periods.