What Indoor Air Pollutants Are Most Harmful to Humans?
- Dan Dearden
- Oct 15
- 3 min read
By Dan Dearden, CAFS
As a longtime HVAC technician, I’ve spent years learning about the invisible substances that affect the air we breathe indoors—some of which can be surprisingly harmful to your health.
Ozone: The First Culprit I Encountered
Early in my career, I learned about ozone (O₃), often produced by malfunctioning electronic air cleaners (EACs). I could often walk into a home and immediately smell that sharp ozone odor—a sure sign the EAC wasn’t working properly. The best way to keep ozone out of your home? Only use devices that are certified ozone-free. And if you already own equipment that produces ozone, remove it.
Then Came VOCs
Later, I learned about volatile organic compounds (VOCs)—chemicals that easily evaporate into the air. They come from things like paint, cleaning products, furniture, and building materials. The best strategy is to eliminate the source wherever possible. If that’s not enough, install an energy recovery ventilator (ERV) to bring in fresh, filtered air from outside.
Not All Pollutants Are Equal
For years, I treated all indoor pollutants as equally harmful. But a scientific study changed that perspective. Researchers found that some pollutants are far more damaging to human health than others.
Let’s say you had $4,000 to spend on improving your home’s air quality. You could invest it in removing VOCs, or in reducing particulate matter (PM2.5 and PM10). Here’s why that choice matters:
VOCs account for less than 1% of the total harm to humans caused by indoor air pollutants.
Particulate matter (PM2.5 and PM10)? It causes 86% of the harm.
That’s a massive difference.
This data comes from the scientific study "Harm From Residential Indoor Contaminants," published by ACS Publications. Fortunately, Dr. Allison Bailes of Energy Vanguard translated the complex study into layman’s terms in his article, “The 6 Worst Indoor Air Pollutants.” It’s a great read if you want to dive deeper. I highly recommend it.
What the study shows is that of the top 45 indoor air pollutants, 7 cause the most harm to humans. See my chart below:
The 7 Most Harmful Indoor Air Pollutants
The original study highlights six major pollutants, but based on the data, I believe mold deserves its own category. While technically grouped with other pollutants in the study, mold’s harm level is over five times higher than anything else in that group.
So here’s my list of the seven indoor pollutants that pose the most harm:
PM2.5 (fine particulate matter)
PM10-2.5 (coarse particulate matter)
Nitrogen Dioxide (NO₂)
Formaldehyde
Radon
Ozone
Mold
VOCs (still worth considering, but less harmful than most think)
(Note: PM2.5 and PM10-2.5 are both forms of particulate matter and often grouped together as PM.)
How to Reduce the Worst Pollutants in Your Home
Now that we know what pollutants matter most, we can focus on the solutions that offer the best return on investment:
✅ Particulate Matter (PM2.5 and PM10)
Install a HEPA-level air filtration system like the NovusAer.
Use a home depressurization duct to prevent particles from entering the indoor air space.
✅ Nitrogen Dioxide (NO₂)
Eliminate open combustion appliances like gas stoves and ovens.
Avoid idling or operating gasoline or propane-powered vehicles near your home such as automobiles and lawncare engines.
✅ Formaldehyde
Choose certified formaldehyde-free products: flooring, furniture, insulation, and construction materials.
Eliminate open combustion appliances like gas stoves and ovens.
Avoid idling or operating gasoline or propane-powered vehicles near your home such as automobiles and lawncare engines.
Add an ERV to bring in clean outdoor air and reduce buildup.
✅ Radon
Use a subfloor depressurization system to vent radon from beneath your home.
✅ Ozone
Only purchase air-cleaning devices that are ozone-free certified.
Remove any devices that produce ozone.
✅ Mold
This one’s tricky. I recommend contacting a professional mold mitigation specialist—they can assess and safely remove mold from your home.
The Environmental Protection Agency, EPA, has a great guide for homeowners to help prevent and clean up mold. https://www.epa.gov/mold/brief-guide-mold-moisture-and-your-home
✅ VOCs
Avoid products that contain VOCs (paints, adhesives, cleaners, etc.).
Choose low- or zero-VOC alternatives when possible.
Again, an ERV can help dilute VOCs by bringing in fresh air.
Final Thoughts
Not all indoor air pollutants are created equal. By understanding which ones pose the greatest risks, you can make smarter choices about how to improve your indoor air quality—and protect your family’s health.
If you're considering upgrading your home's air quality system, start with the pollutants that matter most. And if you have questions, Essential Air Products is here to help you breathe easier.
Comments