(WHO), more than 7 million premature deaths occur every year due to air pollution.

While we often consider “air pollution” to be something that impacts us only outdoors, pollutants from outdoor air collect and concentrate indoors, often making indoor exposure even more impactful to health. Using a common tool designed to assess and manage outdoor air pollution – the air quality index (AQI) – you can also help improve the quality of our indoor air.

The purpose of the AQI is to help you understand what local air quality means to your health. In the US, the AQI is administered by the Environmental Protection Agency (EPA).

The AQI is calculated using four major air pollutants that are regulated by the Clean Air Act: ground level ozone, particle pollution, carbon monoxide, and sulfur dioxide. At www.airnow.gov the EPA is constantly monitoring and rating how much of each pollutant is in the air for your zip code. They quantify their assessment on a scale of 0 to 500:

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The higher the AQI value, the greater the level of air pollution and the greater the health concern. For example, an AQI value of 50 represents good air quality with little or no potential to affect public health, while an AQI value over 300 represents air quality so hazardous that everyone may experience serious effects.

How can I use the AQI to improve my indoor air?

If you see your local AQI above 100 (sensitive groups) or 150 (most others) signaling unhealthy air, you’re generally better off being indoors. However, since many studies show that pollutants concentrate indoors at 2-5x (and up to 10x) their outdoor levels, staying inside may not be enough.

Once you see the AQI reach a worrying number, there are steps you can take to protect your indoor air quality:

If you absolutely can’t stay indoors when the AQI is bringing bad news, follow two important precautions: