AirGradient Forum

Pm2.5 changing a lot, is my indoor air that bad? [solved, it's the ultra-sonic humidifier causing high pm2.5]

#1

My local weather forecast’s PM2.5 has always been <10 ug/m3 for the last few days. I have an indoor air gradient monitor v9. The pm2.5 has been fluctuating a lot. from 0 ug/m3 to 250 ug/m3. I live in a non-industrial area without any factory within 10 km. Here is a typical 24 hours plot:

20250326_pm2_5_plot
20250326_pm2_5_plot878×798 62.4 KB

I have also upgrade the firmware to the latest version 3.1.13. It’s still the same. I also opened the window, but it didn’t make a difference.

Did I forget any configuration? I don’t have a 2nd monitor to confirm the reading. Thank you very much!

#2

If you open the window during high indoor readings and you do not observe a change, then it suggests the PM comes from outside. The pattern you share is possible, for example if there is a source nearby and the wind direction changes.

Maybe the points below help:

  • compare with sensors nearby on the AirGradient map (or other maps)
  • Are there potential sources nearby? Fires produce a lot of PM. Maybe a neighbour who heats by burning something? Or a farmer burning something?
  • Do you have a source indoor? Candles? Also steam from hot water produces particles that might be picked up as PM (shower, kitchen)
  • does your sensor respond to PM as it should? You can extinguish a candle or spray some deodorant/fragrance to see if the sensor spikes. You could do that during periods of low PM
#3

Thank you very much for your reply.

  • The nearby map shows 7 ug/m3

  • The monitor is in the bedroom. No kitchen or other potential source that I can think of. I’m find anyone nearby burning anything near by.

  • I can certainly do more testing with candle, cooking, and car exhaust

#4

Looks like it goes up around bedtime until morning, which would make sense for a bedroom.

Shower at night or any bedtime prep that involves aerosols or alcohol products, such as cologne/perfume, anti-perspirant, fingernail polish remover, humidifier, etc?

1 Like
#5

Thank you so much, MallocArray! You nailed it! It’s the ultrasound humidifier in my room.

I tested it again. Please see the pm2.5 results:

20250327_humidifier_affects_pm2_5
20250327_humidifier_affects_pm2_51687×743 62.8 KB

Time to invest in an evaporative type humidifier

#6

Hopefully one of the AirGradient scientists can reply as well, but I don’t think the water vapor from an ultrasonic humidifier is particularly dangerous, but the sensor detects it just like it would solid particles that are dangerous.

Not sure if that means it is better to have a different type so you can pick out more dangerous particles or not.

#7

I am glad this is resolved and I agree with MallocArray.

An ultrasonic humidifier operates by emitting tiny airborne water droplets that eventually evaporate and increase RH. The water itself is harmless for our lungs. If you use tap water in your humidifier, then there will be some minerals that become airborne (although with quite low masses). These minerals solidify as the water droplet evaporates.

I think there is currently no scientific consensus whether these minerals pose a risk or not. Personally, I believe the risk is relatively low, especially compared to PM from a candle or an unfiltered car tailpipe. These minerals were dissolved in water to begin with, so it seems reasonable to assume that most of these minerals will dissolve again in our lungs and become part of our natural metabolism. In other words, I think these particles will probably not accumulate in our lungs. But I think no scientist managed to prove or disprove this opinion yet.

As an alternative, an evaporative humidifer operates by emitting gaseous water into the air. In consequence, no minerals become airborne.

#8

I was surprised when I got my first indoor Air Gradient to see the ridiculously high PM2.5 reading after first switching it on as there was nothing happening (cooking etc.) at the time that could cause that. A process of elimination proved that it was my ultrasonic humidifier(Govee) that was about six feet away that was the culprit, although I didn’t know why. After switching the humidifier off and ventilating the room, the PM2.5 readings dropped to near zero. I left my humidifier off after that.

Reading up on it I discovered the reason and that explained why Govee stated in the manual that the area around the humidifier might end up with fine white dust.

#9

Thank you all for the insight.

I found this results. Paper id: “ina.13129”. Sorry the forum doesn’t allow me to paste the link.

Basically the paper says it’s un-conclusive if ultra-sonic based humidifier-induced pm2.5 is bad for health or not. So, no clear definition yet.

However as a precaution, I’ll consider replace it with another type. The rational is that historically many things were not considered bad, but later found bad. Examples are asbestos, lead, BPA, etc.

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#10

Is it possible (but maybe far fetched) that this tap water contains legionella pneumophila bacteria that wouldn’t cause harm in drinking water but will in your lungs?

#11

Bioaerosols are out of my expertise, but I know researchers who study that.

According to my understanding:
Whatever is dissolved/dispersed in the water, it will become airborne when aerosolised by an ultrasonic humidifier. This includes also microorganisms. Given that the immune system in the lungs is different from the gastrointestinal tract, I would assume that microorganisms could be harmful for the former but not for the latter (or vice versa). However, I think the same is true for tap water aerosolised by a shower head or when we flush the toilet. Yes, a toilet probably emits less respirable particles than a humidifier, but it typically contains stuff that is not found in tap water.

The lack of a scientific consensus does not necessarily imply that something poses a significant health risk. Many things lack consensus because it is simply not studied: maybe there is not enough motivation to begin with or there are no suitable scientific methods. I mean there is also no scientific consensus about the non-existence of unicorns: it is really hard to prove the non-existence of something.

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#12

Speaking from experience my father almost died from legionnaires disease. I am well aware of the dangers associated with poorly maintained HVAC and humidifiers.

That being said I use a combination of ultrasonic humidifiers in small spaces and evaporative ones in large spaces. I work pretty hard to keep the RH in my house around 40% year round for my comfort and the health of my pets and plants.

With chlorinated/treated municipal tap water and an NSF 53 under sink water filter I feel the risks are well mitigated. The importance of cleaning your humidifiers cannot be understated though.

Also @Siriel_AirGradient lol :joy:

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#13

And you’re obviously putting COLD tap water in your humidifier, which greatly limits the risk too, I don’t know why it had slipped my mind yesterday

#14

While it is true I use cold water, that can probably go either way. I’m not sure hot water would pose an additional risk at all, it might even be better in some situations.

I keep my hot water heater at 140F (60C). Theoretically, if I used hot water and I suspected my tap water was contaminated that high of a temperature should reduce the risk of pathogens. This temperature happens to also be around what you would consider safe cooking temperature for some meats, in beef this is about “Medium Well”.
If 140F/60C going to kill pathogens in meat it should also kill pathogens in the water supply. :slight_smile:

You are right tho, Legionella specifically does do well at higher temperatures 122F/50C but at 60C they don’t do so well. If you have well water or suspect your water supply, 158F or 70*C is a safer option.

Strains of L. pneumophila have been shown to have a decimal reduction time (D)4 of 80–124 minutes
at 50 ºC, and of 2 minutes at 60 ºC (Dennis, Green & Jones, 1984; Schulze-Robbecke, Rodder
& Exner, 1987).

ChatGPT:

The decimal reduction time (D-value) represents the time required to reduce a bacterial population by 90% (1 log reduction) at a given temperature.

Legionella pneumophila D-values at Key Temperatures:

  • 50°C (122°F): 80–124 minutes → Slow reduction; some bacteria survive for hours.
  • 60°C (140°F): ~2 minutes → Rapid reduction; most bacteria are eliminated quickly.
  • 70°C (158°F) and above: Instant kill → Used for thermal disinfection.

These findings are supported by:

  1. Dennis, Green & Jones (1984)
  2. Schulze-Robbecke, Rodder & Exner (1987)

These studies reinforce why water systems should be maintained at ≥60°C (140°F) to control Legionella growth. Would you like references to more recent studies or guidelines on thermal disinfection?

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#15

Indeed, it depends how hot your hot water is.

While 60°C was the recommendation for a very long time everywhere, authorities in many countries have lowered it recently to save the polar bears. For instance, I seem to recall the CDC recommends 140°F (so 60°C) while the DOE says 140°F (barely 50°C).

But the recommendations from government agencies aren’t what matters the most, the actual use of equipment is. And while I don’t know how people use their stuff, I know some modern smart water heaters accept to go WAY lower than 50°C. Here’s a Teka that regulates between 30°C and 75°C: https://www.teka.com/global/product/ewh-50-ve-d_42080320/

And a GE between 100°F and 140°F:

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#16

You’re not wrong, but the science is clear here. I solved this problem by buying a more efficient hot water heater. I have a Rheem 40 gallon “smart” heatpump/hybrid hot water heater. My electric company gave me a 500 dollar rebate and my state has a seperate rebate program where I got an additiona 250 dollar rebate. All in it cost less than a regular resistive heat hot water heater!

https://www.homedepot.com/p/Rheem-Performance-Platinum-40-Gal-Smart-High-Efficiency-Hybrid-Heat-Pump-Water-Heater-with-10-Year-Warranty-XE40T10H45U1/330317336

It can do just heat pump, just electric resistive or a combination. I use the “high demand” option which uses the combination of both. But you’re right, It actually warns you when you go above 120*F that you have a “scald” risk. I ignore this and set it to what I want. This was probably because of some DOE recomendation or something. I prefer not giving pathogens the opportunity to colonize my plumbing. :slight_smile:

This also has the benefit of allowing you to use less harsh chemicals when washing clothes and dishes. Simple soap and water works wonders with hot water, no need for chemical detergents and I now use far less bleach. But now I am in the weeds :slight_smile: