Your air purifier cleans more on “always on”
A 2026 study in Toronto tested the same air purifiers in 60 homes, one setting at a time. Here is what it found, and what it does not tell us.
The short answer
When the purifier ran all the time, the tiny particles in the air went down by about two thirds. On auto, they went down by less than half. The change is one button.
What the scientists did
They put a portable air purifier in 60 apartments in three buildings in Toronto, Canada. Each home tried three settings, one week each, in a random order:
Sensors measured the fine particles in the air (called PM2.5) all day and all night. These particles are so small you cannot see them. They come from cooking, smoke, traffic and dust.
What they found
Drop in fine particles each week, compared with the purifier off:
The small lines show the likely range: 59–72% for always on, 27–50% for auto.
Why auto does less
On auto, the purifier slows down or stops when its sensor thinks the air is clean. It is quieter and uses less power, but it runs for less time. Less running time means it removes fewer particles.
What this study does not show
- It did not measure health. It measured the air, not how people felt or whether they got sick.
- Homes were very different. On always on, the drop ranged from 14% to 100% from home to home. Your result may be bigger or smaller.
- One city, one kind of home. These were apartments in three Toronto buildings, with one week per setting.
- Only fine particles. It says nothing about gases or smells.
- Funding. The study was paid for by a public research council in Canada. An air purifier company gave the researchers cheaper filters.
What you can do
- Try always on in the room where you spend the most time.
- If the noise bothers you at night, choose a low, steady speed instead of auto.
- Change the filter when the maker says. A full filter cleans less.
These are our suggestions based on the study, not medical advice.
Source: Mendell AY, Lee S, Siegel JA. The impact of portable air cleaners on indoor particulate matter concentrations and perceptions of indoor air quality: a randomized crossover trial in three multifamily buildings. Journal of Exposure Science & Environmental Epidemiology, 21 April 2026. Read the study (free)
From Evmara
We publish a new plain-words guide most weeks. Leave your email and we'll send each one as it comes out.