Have you ever wondered about the number on your air purifier? Brands like Levoit, Xiaomi, and Philips show live air quality readings. But what do these numbers really tell us, and can we trust them?
In this article, we’ll explain what that number means on your air purifier. But a quick heads-up: as we’ll discuss in section 3, these numbers can sometimes be a bit off.
1) What are the Readings On My Air Purifier?
Air purifiers with built-in air quality sensors typically display one of two numbers: 1) 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 over 15 micrograms daily is 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).
AQI “Air Quality Index”
Air purifiers such as the Philips air purifier display AQI. AQI stands for “air quality index”. The issue with AQI is there are multiple AQI standards around the world. Philips for example uses the more lenient Chinese AQI standard in many of their air purifiers. That means the number on your air purifier will tell you a better air quality than it would be under the US AQI standard.
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 over the limit. 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 annual limit of 5 micrograms!
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 Philips 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 4 Max Air purifier in Pilates Classroom
The Smart Air team did a simple test with the Xiaomi 4Max. With the window open (72 micrograms outside) and the indoor purifier turned on, the built-in air quality monitor of the Xiaomi showed 1 microgram, while the QP Lite Air Quality Monitor showed 48 micrograms. The difference is 48 times, indicating that the Xiaomi 4Max’s built-in monitor cannot accurately reflect the actual air quality in the room.
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:
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