Connecting Lake Simcoe's Community

Font size: +

Science in the Making

Have you ever wondered how something works or whether or not what you’ve heard is actually true? This is the first in a series of posts that I will be sharing that have been written by two of our exceptional professors, and members of our Sustainability Sciences Department, Dr. Chris Murray (left) and Dr. Thamara Laredo.


This week’s post will address a question that may be on the minds of many during seasons of dry air, runny noses, and persistent coughs: do ultrasonic (filterless), cool mist humidifiers fill the air with dust? If so, is this dust dangerous to our health?

At first, the questions might seem like a simple one to solve with a science experiment: get a cool mist, ultrasonic humidifier and run it with tap water, then measure what comes out. But the process is not as straightforward as it seems. Before we get to the experiment, you should know a little about how this type of humidifier works.

There are significant differences between a warm mist humidifier (which works essentially like a kettle) and a cool mist humidifier. A cool mist humidifier produces sound waves that are broadcast into the water, and the vibration causes the water to essentially break up into particles that are so small they escape into the air by diffusion. As a tiny droplet of solution escapes the humidifier, the water will quickly evaporate but any dissolved minerals in the water could remain in the air. Why might this be of concern? Substances that are non-toxic in big pieces can often be very dangerous when they are turned into small particles. They remain in the air for a long time, can be breathed in, and chronic exposure can cause serious health effects.

For this experiment, we ran the cool mist humidifier with as pure a sample of water as possible, directing the mist towards a mirror we hoped would make it easy to see anything that might come out. As you might expect, the mirror was quickly covered by water droplets. When the water evaporated, though, there was nothing but a clean mirror. To make things easier, we “doped” a sample of water with a solid that would readily dissolve (in this case we used calcium carbonate, which is similar to baking soda) and is easy to measure the concentration of in water. We ran the humidifier again and almost immediately started to see white residue collecting on the mirror.


As the ultrasonic humidifier ran longer and longer, the concentration of dissolved material in the water remained constant, indicating that the dissolved salt was being expelled in tiny mist droplets. Both the qualitative observation of white powder landing on the mirror and all around the humidifier and the quantitative measurement of unchanging solute concentrate support the suggestion that ultrasonic humidifiers do have the potential to fill the air with small solid particles.

So what does this all mean? The answer to that is a little complicated. We can say for certain that yes, ultrasonic humidifiers do indeed release particles into the air we breathe. But does this mean they are unsafe? Not necessarily – in order to answer that question confidently, we would need to conduct multiple experiments on particle size and their effect on humans.

If you have a question you think our science profs could answer, please let us know! Email me or comment below and I will forward your query to Dr. Laredo and Dr. Murray.


Stay Informed

When you subscribe to the blog, we will send you an e-mail when there are new updates on the site so you wouldn't miss them.

Students Showcase Original Research
Stop the bullying

Get Your Free Subscription! Delivered Straight to
Your Inbox.

Enter your email to receive updates from us. You can unsubscribe at any time.