What Does the Number On My Air Purifier Mean?

What is the meaning of that number displayed on your air purifier? Many popular air purifiers including Xiaomi and Phillips display live air quality readings. But what exactly do these numbers mean and are they even accurate?

In this article, we break down everything you need to know about that number on your air purifier. But first, a little warning: as mentioned in section 3, numbers on air purifiers are often inaccurate.

1) What is the Meaning of the Number On My Air Purifier?

Air purifiers with built-in air quality sensors typically display one of two numbers: 1) Micrograms of PM2.5 in the air OR 2) AQI.

Micrograms of PM2.5

Popular air purifiers such as Xiaomi air purifiers display micrograms of PM2.5 in your air. The WHO also uses micrograms to set their PM2.5 air quality guidelines. According to the WHO, PM2.5 levels over 5 micrograms are dangerous. Therefore, it is best to keep the number on your Xiaomi air purifier below this number. Do not trust the green color signals used by Xiaomi or other air purifiers (see below).

What does the number on my air purifier mean?

AQI

Air purifiers such as the Phillips air purifier display AQI. AQI stands for “air quality index”. The issue with AQI is there are multiple AQI standards around the world. Phillips for example uses the more lenient Chinese AQI standard in many of the air purifiers. This results in the number on your air purifier showing the air quality as better than it would under the US AQI standard.

What does the number on my air purifier mean?

So what AQI should you aim for in your home? According to the WHO, a US AQI over 21 or a China AQI over 7 is dangerous. Unsure whether the AQI number on your air purifier is US or China AQI? Then best to assume it is the Chinese standard and aim for an AQI under 7.

2. What is the Meaning of the Light On My Air Purifier?

Along with a number, many air purifiers also have lights to indicate how safe the air is. We recommend ignoring these lights and focusing on the air quality numbers we mentioned above. The lights on many air purifiers are often based on extremely lenient air quality guidelines. For example, Xiaomi air purifiers indicate 35 micrograms of PM2.5 as healthy green. In reality, this means you are breathing air 7-times the WHO recommended limit of 5 micrograms!

What does the number on my air purifier mean?

3. BUT…Take Your Air Purifier’s Number With a Grain of Salt

Our tests show air quality sensors in popular air purifiers are quite inaccurate. We tested the Phillips and Xiaomi air purifier sensors and found they were particularly inaccurate at higher levels of pollution. For more accurate readings, we recommend using a standalone PM2.5 air quality monitor. Air purifier companies typically use cheap, inaccurate sensors as their built-in sensor.

Read More: The Best and Most Accurate PM2.5 Air Quality Monitors

Xiaomi air purifier sensor inaccurate

Why Smart Air Does Not Include Air Quality Monitors in Purifiers

At Smart Air, we do not include any air quality sensors in our award-winning air purifiers. As a social enterprise, our goal is to provide the most effective air purifiers on the market at the lowest possible cost. We are not willing to add a cheap inaccurate sensor that is both a gimmick and adds to the price. For accurate air quality readings, we recommend using a dedicated air quality monitor with data backing its effectiveness.

See Smart Air founder and University of Chicago professor Thomas Talhelm discuss the Smart Air mission:

How Much Should Clean Air Cost? Innovating Affordable DIY Purifiers - Thomas Talhelm

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Smart Air is a social enterprise that creates simple, no-nonsense air purifiers and provides free education to protect people’s health from the effects of air pollution. We are proud to be the only certified B-Corp dedicated to fighting air pollution.