What Goes Into Our Lungs? My Experience With an Air Purifier
From a reading above 200 in Bangkok to around 7 near the beach in Hua Hin
Affiliate disclosure: This article may contain affiliate links. If you buy through a link, I may receive a commission at no extra cost to you. My personal experience is not a guarantee of the same result in another home.
We talk a great deal about what we eat. We choose our vegetables, compare ingredients, and pay attention to nutrition. But what about the air we breathe?
My interest became practical when I bought a Xiaomi Mi Air Purifier 3H while living in On Nut, Bangkok.
When I first switched it on, the display showed a number above 200.
I was indoors. I had expected the air inside my home to be cleaner than the air outside. That reading made me reconsider the assumption.
The balcony door made a difference
After I ran the purifier, the reading dropped substantially. I also learned to keep the balcony door closed when the outside air was polluted.
In my experience, the readings then stayed low over the following years. I cannot reconstruct the exact pollution sources or independently verify those old measurements. Nevertheless, the change taught me something useful: a purifier and the way I managed the room worked together.
Outdoor particles can enter through doors, windows, and other openings. Indoor sources—including frying, smoking (no, I don’t smoke), incense, and candles—can add particles of their own.[1] Walls do not automatically make indoor air clean.
A different experience in Hua Hin
Today, I live in Hua Hin, about 100 metres from the beach. I usually keep my doors open to the outside.
I now often switch the purifier on to check its reading rather than because I expect it to need substantial cleaning. After about five minutes, the display is around 7. That is a number I am comfortable seeing.
This is an observation in my home at the time of checking, not a claim that every coastal home has clean air. Being close to the sea does not prevent pollution from traffic, smoke, cooking, or other sources.
There is another detail worth remembering: when I turn the purifier on, it begins filtering while it measures. The number after five minutes is therefore a reading during operation, rather than a completely independent measurement of the room before filtration.
What do 200 and 7 actually mean?
The Mi Air Purifier 3H displays an estimated PM2.5 concentration in micrograms per cubic metre, written µg/m³.[2]
PM2.5 refers to fine airborne particles up to approximately 2.5 micrometres in diameter.
| Display | Meaning |
|---|---|
| 200 on the 3H | An estimated indoor PM2.5 concentration of 200 µg/m³ |
| 7 on the 3H | An estimated indoor PM2.5 concentration of 7 µg/m³ |
| 200 AQI on a website | An air-quality index score, not 200 µg/m³ |
The purifier is a household instrument, not a laboratory monitor. Placement, sensor condition, water mist, and cooking fumes can affect readings.[3]
WHO's PM2.5 guideline levels are 5 µg/m³ for an annual average and 15 µg/m³ for a 24-hour average.[4] These are exposure guidelines, not pass-or-fail limits for one five-minute reading. A reading of 7 is encouraging, but it cannot establish the day's average or prove that all pollutants are absent.
The 3H's green indicator also covers a broad range, up to 75 µg/m³.[2] I pay more attention to the number than to the colour.
What about furniture glue and gases?
When I saw a high reading, I wondered about gases from glued furniture.
That is a separate concern. Some composite-wood products can emit formaldehyde, but the 3H's particle reading does not directly measure it.[5] Nor is that display a carbon dioxide monitor.
A particle filter addresses airborne particles. Gas removal requires suitable gas-filtering material, such as activated carbon, and performance depends on the pollutant and filter design. No purifier removes every indoor pollutant or replaces ventilation and source control.[6]
A low particle reading is useful information. It is not a complete certificate of clean air.
The small maintenance problem that fooled me
At another point, after I bought a replacement filter, the reading seemed too high.
Following advice to check the sensor opening, I blew through a straw into that area. Afterwards, the readings returned to what I expected.
That was my experience, but I would not turn mouth-blowing into a maintenance recommendation: breath can introduce moisture. Instead, follow the cleaning instructions for your model.
Xiaomi confirms that dust or debris in the laser-sensor compartment can affect accuracy and recommends cleaning that compartment.[3] Switch off and unplug the purifier before maintenance, and avoid introducing liquids or poking objects into the sensor.
My lesson was simple: an unexpected number may deserve a sensor check as well as a filter check.
How to choose a purifier without overspending
An air purifier can be a useful purchase when particles are a recurring problem. The right choice depends on the room and how you will use it.
Before buying, compare:
- Particle CADR: clean air delivery rate should suit the room size.
- Noise at the speed you will actually use: an impressive maximum setting is less useful if it is too loud.
- Replacement-filter cost and availability: include them in the ownership cost.
- Pollutants addressed: particle filtration and gas filtration are different capabilities.
- Ozone emissions: avoid devices intended to generate ozone.[6]
A PM2.5 display is helpful for observing changes, but it should not be the only reason to buy. If monitoring is your main goal, a separate particle monitor may be more appropriate.
For filtering, keep doors and windows closed when outdoor air is polluted. Ventilate when outdoor conditions are better; opening everything during a pollution episode can undermine filtration.
A place for an air purifier in healthy retirement
My experience does not tell everyone to buy the same machine. It tells me to pay attention to the air in the home I actually live in.
In Bangkok, the purifier and a closed balcony door helped me manage the particle readings. In Hua Hin, my current checks are much lower, and I can adjust my use accordingly.
Healthy living includes what goes into our lungs as well as what goes onto our plates.
Compare purifiers for your room
Look for a suitable particle CADR, clear filter specifications, affordable replacement filters, and a noise level you can live with.
Product link: To be added after confirming the seller, model, filter availability, and affiliate link.
Sources and further reading
- EPA: Sources of Indoor Particulate Matter
- Xiaomi: Mi Air Purifier 3H manual
- Xiaomi: Troubleshooting inaccurate 3H readings
- WHO: Air-quality guideline levels
- EPA: Formaldehyde and indoor air quality
- EPA: Guide to Air Cleaners in the Home
- NutritionFacts.org: Air pollution topic page — additional reading; not the source of the device specifications or buying criteria.
Draft for HealthyRetired.com. Personal readings are recollections and observations, not independently verified measurements. Affiliate links have not yet been inserted.