Do Air Purifiers Dry Out the Air?

Empirical data shows that air purifiers are great at cleaning air, but do they dry out the air and lead to other health problems? For me, dry air is mostly just a comfort issue. But for some people, dry air can exacerbate health problems like allergies and bronchitis.

Do HEPA Filters Lower Humidity?

To test how turning on an air purifier affects humidity, we first burned cigarettes to pollute a sealed room…

Then we turned on the Blast Mini HEPA air purifier for 25 minutes.

During the test, we used the AirVisual Pro laser particle counter to track particulate pollution and humidity.

In 20 minutes, particulate pollution dropped from nearly 200 micrograms to zero (red line). But humidity did not drop at all (blue line).

Dry noses rejoice!

Do Carbon Filters Dry out the Air?

But that was just a simple HEPA purifier—a fan and a HEPA filter.

Things get a little bit more complicated if we add a carbon filter. Carbon filters remove gas pollutants like formaldehyde, VOCs, NO2, and ozone.

Why is it more complicated? Carbon adsorbs these gases onto the surface of the carbon.

It seems plausible that activated carbon could adsorb water vapor too.

But hey, lots of things are plausible! So we tested it.

We used the Blast because it has a massive carbon filter. The Blast’s carbon filter packs in a whopping 1.1 kilograms of activated carbon.

With such a large carbon filter, we can detect even a small effect on humidity.

The Blast did a quick job of cutting the pollution in the room. The Blast cut particulate from 250 micrograms to zero in about 15 minutes. Meanwhile, humidity dropped 2%.

Thus, carbon seems to reduce humidity slightly. That makes sense with theory. Activated carbon is hydrophobic, meaning it does not attract water molecules. But activated carbon also has some oxygen in it, which attracts a little bit of water. When scientists tested it in the lab, they found that only a little bit of water vapor adsorbed onto the carbon.

Caveat: if an air purifier or fan blows air directly onto your body, it can increase evaporation from your body and make you feel dry. There’s an obvious fix: point the air purifier another direction!

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