What is Air Quality Index (AQI)?

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Every government uses a scale to measure the quality of the air in their country. They do that via using a special index, called the Air Quality Index (AQI).

Air Quality Index (AQI) is an index that tells us the quality of the air. It determines the percentage of pollutants in the air, and tells us how polluted the air is and the associated risks of breathing the air. Also, it helps us understand and present the forecast of air quality for the future.

In this article, we will take a closer look at AQI – what it is, how it is used and by whom, and why is it even used. Also, we’ll see where in the world the air quality is the worst and where it is the best, giving you a better sense of how AQI can help us determine the quality of life.

Air Quality Index – AQI

Air Quality Index is an index for reporting the daily quality of air. It requires complex measurement systems and devices that can only be bought by bigger companies and government agencies. These devices measure the levels of pollutants in the air on a daily basis, and then they are compiled together by the AQI.

The AQI basically tells us the quality of air that we breathe in our location, and it predicts what the quality will be in the days to follow. The AQI, for example, will increase on the days where various air emissions are predicted to increase, such as during the rush hour or if there is an upwind forest fire nearby.

The index has a scale from 1-10 to indicate the pollution levels. The lower numbers tell us that the health risk of inhaling air is low, while the increasing numbers present the increasing health risk connected to air pollution. This scale is the most commonly used; however, many countries utilize different scales to predict air pollution.

For example, the UK has a 1-10 index scale, while Singapore has a 1-400 scale. South Korea has a 1-500 scale, for example. But the main premise stays the same: the higher the number, the higher the health risk is.

What is Normal Air Quality Index?

The index scale tells us how dangerous it is for us, or how safe it is to breathe the outside air. As we already mentioned, there are several scales, and all have the same way of predicting the risk. The higher the number, the higher the risk.

Also, the safety risk levels are associated with colors. Here are the most common safety levels that are found on an Air Quality Index (we will use a 1-10 scale for this example.)

  • 1-3: Low risk. The air quality is relatively good, and the health risk is low. Green color.
  • 4-6: Moderate risk. The air quality is somewhat compromised and may be risky for sensitive groups. Yellow color.
  • 7-10: High risk. The air quality is poor and the outdoor activities should be reduced. Orange color.
  • 10+: Very high risk. You should avoid all outdoor activities as the air quality is extremely poor and dangerous to your health. Maroon/red/black color.

As we can see, the normal, or acceptable air quality is usually found on the green or yellow part of the AQI. If the risk is higher, we should listen to the warnings and regulations that are published by our local government.

What Causes Air Pollution?

Air pollution is caused by solid and liquid particles, called pollutants, that are emitted from various sources. They can come in various shapes and sizes, and various gases are also common when it comes to pollution. Here are some of the most common pollutants:

  • Ozone
  • Smog
  • Dust
  • Pollen
  • Smoke from factories
  • Vehicle emissions

These allergens are the most common, but there are plenty more to be found. Ozone is a big problem as it is somewhat hard to control, and is the problem of the whole planet, not just of big cities.

However, big cities and areas around power plants or other industrial plants are far more likely to have higher pollution levels. Sadly, this pollution will also be transferred to other places on the Earth with the help of strong winds that will carry the particles around.

How to Measure Air Quality?

As we already said, air quality is measure by the AQI. However, there are various tools and instruments that are required to measure air quality.

Namely, there are certain instruments on the ground and in the air that measure the air quality. One of the most common ways of measuring air quality are satellites that will monitor the particles in the air. For example, a very important satellite to measure air quality is the Joint Polar Satellite System.

Cities with Worst Air Quality

Thinking of moving to a big city? Think again, as the air pollution in big cities is a massive problem nowadays. Especially the countries in Asia, the big cities will have extremely high levels of pollution. These are the cities with the worst air quality.

  1. Dhaka, Bangladesh.
  2. Delhi, India.
  3. Kolkata, India.
  4. Yangon, Myanmar.
  5. Mumbai, India.
  6. Lahore, Pakistan.
  7. Chiang Mai, Thailand.
  8. Tashkent, Uzbekistan.
  9. Dubai, UAE.
  10. Poznan, Poland.

Some of the other big cities in the list include Krakow, Hanoi, Guanzhou, Nur-Sultan, Beijing, Milano, Bangkok, Seoul, Osaka, Kyiv, and more.

Cities with Best Air Quality

On the flip side, here are cities with best air quality.

  • Honolulu, Hawaii.
  • Halifax, Canada.
  • Anchorage, Alaska.
  • Auckland, New Zealand.
  • Brisbane, Australia.
  • Zurich, Switzerland.
  • Helsinki, Finland.
  • Hamburg, Germany.
  • Reykjavik, Iceland.

Note that these are just some of the examples. It is harder to find cities with clean air than with polluted air.


AQI is an index that tells us how polluted the air is. It is also used for forecasting the air quality, and for telling us what precautions should we take before we go outside. It is a helpful way of knowing what the quality of the air is.

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