Editing Humidifier (section)

===Ultrasonic humidifiers ===
[[File:Ultrasonic Cool Mist Humidifier.jpg|thumb|Ultrasonic Cool Mist Humidifier]]
An ultrasonic humidifier uses a ceramic diaphragm vibrating at an [[ultrasound|ultrasonic frequency]] to create water droplets that silently exit the humidifier in the form of cool fog. Usually the mist gets forced out by a tiny fan, while some ultra mini models have no fans. The models without fans are meant mainly for personal use. Ultrasonic humidifiers use a [[piezoelectric transducer]] to create a high frequency (1-2&nbsp;MHz<ref>{{cite journal |last1=Rodes |first1=C. T. R. G |title=Measurements of the size distribution of aerosols produced by ultrasonic humidification. |journal=Aerosol Science and Technology |date=1990 |volume=13 |issue=2 |pages=220–229|doi=10.1080/02786829008959440 |bibcode=1990AerST..13..220R |doi-access= }}</ref>) mechanical oscillation in a film of water. This forms an extremely fine mist of droplets about one micron in diameter, that is quickly evaporated into the air flow.

Unlike the humidifiers that boil water, these water droplets will contain any impurities that are in the reservoir, including minerals from [[hard water]] (which then forms a difficult-to-remove sticky white dust on nearby objects and furniture). Any pathogens growing in the stagnant tank will also be dispersed in the air. Ultrasonic humidifiers should be cleaned regularly to prevent bacterial contamination from being spread throughout the air.

The amount of minerals and other materials can be greatly reduced by using [[distilled water]]. Special disposable demineralization cartridges may also reduce the amount of airborne material, but the EPA warns, "the ability of these devices to remove minerals may vary widely."<ref name="epa" /> The mineral dust may have negative health effects.<ref>{{Cite web|last=Willis|first=Katie|title=Using tap water in an ultrasonic humidifier may be polluting your air: study|url=https://www.ualberta.ca/folio/2020/11/using-tap-water-in-an-ultrasonic-humidifier-may-be-polluting-your-air-study.html|access-date=2022-01-24|website=www.ualberta.ca|language=en}}</ref><ref>{{Cite journal|last1=Yao|first1=Wenchuo|last2=Gallagher|first2=Daniel L.|last3=Dietrich|first3=Andrea M.|date=2020-12-01|title=An overlooked route of inhalation exposure to tap water constituents for children and adults: Aerosolized aqueous minerals from ultrasonic humidifiers|journal=Water Research X|language=en|volume=9|pages=100060|doi=10.1016/j.wroa.2020.100060|pmid=32793876|pmc=7408721|bibcode=2020WRX.....900060Y |issn=2589-9147}}</ref>  Wick humidifiers trap the mineral deposits in the wick; vaporizer types tend to collect minerals on or around the [[heating element]] and require regular cleaning with [[vinegar]] or [[citric acid]] to control buildup.