AQI Scales Around The World

AQI Scales Around The World

The Air Quality Index, or AQI, is a scale that government agencies globally use to communicate the levels of air pollution to the general public. Generally, AQI readings increase as the concentration of pollutants increases.

Common pollutants most AQI scales consider are carbon monoxide, sulfur dioxide, nitrogen dioxide, Particulate Matter (PM), and ground-level ozone.

Leading institutions, like NASA, use air quality monitors like PurpleAir to measure the concentration of these pollutants and the corresponding AQI values in their regions. Different countries have different scales and ranges due to specific national standards. The public health advisory also changes with these ranges.

Let’s dive deep into what an AQI scale is, what changes its readings, and what some standard AQI scales are from around the world.

What is an AQI Scale?

AQI readings denote the concentration of an air pollutant over a specific time. By observing the concentration and time together, we can obtain the dosage of the pollutant. Using scientific studies that show the effect of corresponding doses on human health, government agencies can convert the reading into an AQI value.

Mostly, these readings are grouped into several categories across a linear scale and are color-coded. Each category represents the severity of air pollution and its effects on human health.

What Changes the AQI Readings?

AQI readings are changeable according to the number of air emissions. For example, when an area receives more traffic during rush hour, the amount of smoke released into the atmosphere rises. As a result, the AQI reading will be higher too.

Other causes of increased AQI values are wildfires, stagnant air, temperature anomalies, anticyclone, and low-speed winds. Wildfires in particular are a significant source of harmful combustion products, while the weather conditions affect the dilution of the pollutants or their stay in one place.

AQI Scales By Country

Around the world, different countries use distinct scales to measure their air pollution standards and issue public health advisories according to them. Here is a brief summary of the AQI scales of a few countries:


The Environmental Protection Agency (EPA) in the United States established an AQI scale that measures air pollution from 0 to 500.

The scale is divisible into 6 categories, where the first category (0-50) represents good air quality and is colored green. The last category (301-500) indicates hazardous levels of air pollution, denoted by maroon color.

2. Australia

Tasmania has the lowest AQI reading in Australia, with the best air quality. The scale is categorized into 6 six categories, where 0-33 represents the weakest pollutants concentration, and 200+ represents the highest.

AQI Description  Color
0-33 Very Good Blue
34-66 Good  Green
67-99 Fair Yellow
100-149 Poor Orange
150-200 Very poor Purple
200+ Hazardous Red


3. India

Like the US, India also has an AQI scale of 0-500 and is divided into 6 categories.

AQI Values  Health Risk Category Colour
0-50 Good Deep green
51-100 Satisfactory Light green
101-200 Moderate Yellow
201-300 Poor Orange
301-400 Very Poor Red
401-500 Severe Maroon


4. Canada

Unlike many countries, Canada's AQI scale denotes emissions levels rather than their implications on public health. The Canadian Air Quality Health Index (AQHI) gives values from 0 to 10+ and is divisible into 4 four categories.

AQHI Value Health Risk
1-3 Low
4-6 Moderate
7-10 High
10+ Very high

AQI Scales Comparison By Country

Country Number of AQI Scale Categories   Number of Pollutants Measured National Standard
US Six Five (Carbon monoxide, sulfur dioxide, nitrogen dioxide, ground-level ozone, PM)  NAAQS (National Ambient Air Quality Standards)
Tasmania (Australia) Six Seven (carbon monoxide, nitrogen oxide, ozone, sulfur dioxide, lead, PM10, PM2.5) National Environment Protection (Ambient Air Quality) Measure (NEPM)
India Six Eight (PM10, PM2.5, nitrogen dioxide, carbon monoxide, sulfur dioxide, lead, ozone, ammonia) National Air Monitoring Program (NAMP)
Canada Four Six (carbon monoxide, sulfur dioxide, nitrogen dioxide, PM, ozone, hydrogen sulfide) Air Quality Health Index (AQHI) 


How to Measure Different AQIs?

To measure AQIs, individuals and businesses can start by investing in the right technology. For example, Air Quality Monitors by PurpleAir measure and show readings according to several global AQI scales.

Plus, the AQI map shows real-time air pollution data according to your location in several AQI scales.

Monitor the Particulate Matter levels around the world with our free, real-time PurpleAir Map or join PurpleAir's mission to make air quality data accessible to everyone by investing in an air quality monitor for your home. 

Together, we can be informed and make changes in our daily habits and the community to improve air quality.