# Ultrasonic Humidifiers **URL:** \ **Category:** Sensors\ **Created:** [October 15, 2021, 5:08pm UTC](https://community.purpleair.com/t/ultrasonic-humidifiers/123 "2021-10-15T17:08:27Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![PurpleAir](https://sea2.discourse-cdn.com/flex020/user_avatar/community.purpleair.com/purpleair/32/176_2.png) [@PurpleAir](https://community.purpleair.com/u/PurpleAir)\ **Post date:** [October 15, 2021, 5:08pm UTC](https://community.purpleair.com/t/ultrasonic-humidifiers/123/1 "2021-10-15T17:08:27Z")
# Ultrasonic Humidifiers and Indoor Particle Readings Some ultrasonic humidifiers can significantly increase particulate matter (PM) levels indoors. In many cases, users notice elevated PM2.5 readings on their PurpleAir sensors while the humidifier is running. This is not a sensor malfunction. The device is detecting real airborne particles generated by the humidifier. ## Why Does This Happen? Ultrasonic humidifiers work by vibrating water at a very high frequency, creating a fine mist that is released into the air. Unlike evaporative humidifiers, ultrasonic models do not filter out dissolved minerals before dispersing the water droplets. If the humidifier reservoir is filled with: - **Tap water** (which contains dissolved minerals such as calcium and magnesium) - **Hard water** - **Water with impurities** - **Dirty or contaminated water** - **A poorly cleaned reservoir** …the humidifier can emit fine mineral particles into the air. When the water droplets evaporate, the remaining minerals become airborne particulate matter — often visible as “white dust” settling on surfaces. These particles are typically in the PM2.5 size range, meaning they are small enough to be detected by PurpleAir sensors and small enough to be inhaled. ## Can This Be Corrected on the Sensor? No. The sensor is functioning correctly and measuring actual airborne particles. Because the particles are physically present in the air, there is no sensor setting or correction factor that can remove their influence. If you observe elevated indoor PM levels while using an ultrasonic humidifier, consider: - Using **distilled or demineralized water** - Cleaning the reservoir regularly according to manufacturer instructions - Switching to an evaporative humidifier, which does not disperse minerals into the air ## Do These Particles Affect Air Quality? Yes. While mineral particles from tap water are not the same as combustion-related pollution (such as wildfire smoke), they still contribute to indoor particulate concentrations. Scientific studies have shown that ultrasonic humidifiers can raise indoor PM2.5 levels substantially, depending on water composition and room conditions. For a detailed scientific analysis, see this peer-reviewed paper: **Particulate matter emitted from ultrasonic humidifiers — Chemical composition and implication to indoor air** > **[Particulate matter emitted from ultrasonic humidifiers-Chemical composition...](https://pubmed.ncbi.nlm.nih.gov/33108019/)** > > Household humidification is widely practiced to combat dry indoor air. While the benefits of household humidification are widely perceived, its implications to the indoor air have not been critically appraised. In particular, ultrasonic humidifiers... This study found that operation of a single ultrasonic humidifier can significantly increase indoor PM concentrations, and in some cases affect the entire household environment. * * * # Additional Resources Below is a collection of scientific studies and articles that further explore ultrasonic humidifiers and their impact on indoor air quality. ## Scientific Studies - [Effect of aerosol particles generated by ultrasonic humidifiers on the lung in mouse | Particle and Fibre Toxicology | Springer Nature Link](https://particleandfibretoxicology.biomedcentral.com/articles/10.1186/1743-8977-10-64) - [Size and Mineral Composition of Airborne Particles Generated by an Ultrasonic Humidifier](https://onlinelibrary.wiley.com/doi/full/10.1111/ina.12414) - [Inhalational Lung Injury Associated With Humidifier “White Dust”](https://publications.aap.org/pediatrics/article-abstract/127/2/e509/65229/Inhalational-Lung-Injury-Associated-With) - [Health Effects of Indoor-Air Microorganisms](https://www.jstor.org/stable/40966495) - [Indoor Particle Concentrations Associated with Use of Tap Water in Portable Humidifiers](https://pubs.acs.org/doi/abs/10.1021/es00174a019) ## Articles - [Ultrasonic Humidifiers: A Source of PM2.5](https://www2.purpleair.com/blogs/news/ultrasonic-humidifiers-a-source-of-pm2-5) - [What You Should Know About Humidifiers and Indoor Air](https://time.com/4685972/humidifier-disinfectants-bacteria-water/) - [White Dust from Humidifiers — Should You Be Concerned?](https://www.hvac.com/air-quality/white-dust-concerned/) # Reducing Indoor Particles with HEPA Filtration If you are concerned about elevated indoor PM levels, using a HEPA air purifier can help reduce airborne particles, including those generated by ultrasonic humidifiers. HEPA filters are designed to capture very small particles, including PM2.5. Running a HEPA purifier in the same room as the humidifier can help lower particle concentrations and improve overall indoor air quality. Effective air filtration does not have to be expensive. In addition to commercially available HEPA purifiers, there are simple do it yourself options that use a box fan paired with high efficiency HVAC filters. These DIY air cleaners can be a cost effective way to significantly reduce indoor particle levels. You can learn more about DIY air cleaner options and indoor air filtration on our blog: > **[DIY Project: How to Make a Box Fan Air Purifier](https://www2.purpleair.com/blogs/blog-home/box-fan-air-purifier)** > > During wildfire season, ventilating our home can be a challenge. Here, we will teach you how to make a box fan air purifier with a DIY project. * * * # Learn More - [Air Quality Index (AQI)](https://community.purpleair.com/t/air-quality-index-aqi/111) - [Why Should I Put My Indoor Sensor on the Map?](https://community.purpleair.com/t/why-should-i-put-my-indoor-sensor-on-the-map/6468) - [What Do PurpleAir Sensors Measure and How Do They Work?](https://community.purpleair.com/t/what-do-purpleair-sensors-measure-and-how-do-they-work/3499) ---
**Author:** ![NileBob](https://sea2.discourse-cdn.com/flex020/user_avatar/community.purpleair.com/nilebob/32/349_2.png) [@NileBob](https://community.purpleair.com/u/NileBob)\ **Post date:** [April 14, 2022, 10:58pm UTC](https://community.purpleair.com/t/ultrasonic-humidifiers/123/4 "2022-04-14T22:58:33Z")
![Humidifier effect](https://us1.discourse-cdn.com/flex020/uploads/purpleair/original/1X/0ec27d667aafcb5654c5fbf531fb5c2f065a4977.jpeg) That’s the nightly elevated PM2.5 levels that I was seeing in our bedroom. Apparently they was caused by the small ultrasonic humidifier we use each night. The higher curve was from a sensor in the bedroom with the humidifier. The lower curve was in another room of our home. So the airborne particulate from the bedroom was circulating through our home. I think we’ll switch to a non-ultrasonic humidifier, both for health reasons and so our sensors can give more useful PM 2.5 readings.