I burned a grilled cheese sandwich recently. I tried to bury the evidence by throwing it in the trash and forgetting about it, but my dear, sweet wife fished it out. “You need to tell the world about this,” she said. “This would be a great blog article to show your readers how something like this affects indoor air quality.”

So, I’m going to take responsibility for this burnt grilled cheese and the—blessedly temporary—collapse of indoor air quality in our home that evening. And I’ll also confess to an even worse collapse earlier this year.

Particulates matter

The first indoor air quality (IAQ) monitors I used to determine if something was wrong were my eyes and nose. It didn’t smell right, and I got a bit of smoke in the house. So that led me to look at electronic IAQ monitors. Here’s what the Awair Element showed.

That spike of nearly 150 micrograms per cubic meter (µg/m^3) in the particulate matter 2.5 micrometers (microns) or smaller, usually called PM2.5, is way higher that any other PM2.5 reading I saw that day.

Then I looked at my Airthings Space Plus IAQ monitor (shown below). It showed an even higher spike in PM2.5, this time at 193 µg/m^3. The PM1 (1 micron or smaller), as you see below, also spiked.

This spike compared to the average

So how does that compare to what the particulate levels usually are in my house? The graph below shows the particulate levels in two size ranges (2.5 microns and 1 micron) for the six months leading up to my burnt grilled cheese catastrophe. The highest PM2.5 peak on there is about 40 µg/m^3.

But there’s a catch here. When you look at more than one day, you’re not seeing the full height of the short-term peaks. Let’s look closer at that red spike in PM2.5 that occurred back in February. It’s at 40 µg/m^3. But that’s the average for that whole day. Here’s what it looks like when I zoom in on what happened only on that day.

Holy moly! We hit 869 µg/m^3 during the worst part of that day. What the heck happened? Here’s what it was:

That’s the opening from the mechanical room in our basement to the (encapsulated) crawlspace. That board floating in the middle started its day resting on top of the two rows of concrete blocks that were removed in the afternoon.

This was part of the demolition in our basement as we began the renovation that month. The contractor also cut open the concrete slab to pour a new footing. They did both jobs with a gasoline-powered saw that spewed fumes and concrete dust throughout the basement. Even with the exhaust fans running and plastic barriers trying to isolate the basement, a lot of particles made their way into the living space above.

And no, I was not happy when I walked into the basement and saw the cloud of smoke and dust hanging in the air.

How quickly can you remove the particles?

In the case of my burnt grilled cheese, the PM2.5 came down to normal levels (less than 10 µg/m^3) in about two hours. The Airthings graph below shows the big peak of 193 µg/m^3 happened at 7:10 pm that day. At 9:10 pm, the PM2.5 was down to 8 µg/m^3.

It took about 14 hours for the PM2.5 levels during the February spike to come down to less than 10 µg/m^3 again. It stayed in the 20s most of the night.

To get the levels down as quickly as possible, you need filtration and ventilation. In our case, we have three MERV-13 filters in our heating and cooling system on the main floor. In the basement, we have exhaust ventilation that was running continuously during the February event. And we have a Corsi-Rosenthal box fan air cleaner that’s been running continuously in our basement since we began the renovation.

On top of that, when something like this happens, you can turn on other exhaust fans in the house to remove the pollutants more quickly. I’m pretty sure we did that in February. I know we did it for my burnt grilled cheese.

The health risks of fine and ultrafine particles

The particles that make up PM2.5 are also called fine particles. The really tiny ones that are 0.1 microns or smaller are called ultrafine particles. The problem with particles this small is that they can penetrate deep into your lungs. From there, they can get into your bloodstream.

The National Academies (Sciences, Engineering, Medicine) came out earlier this year with a thorough report on what IAQ researchers have found out about particulate matter. It’s called Health Risks of Indoor Exposure to Fine Particulate Matter and Practical Mitigation Solutions, and you can download it for free.

Chapter 6 is all about the health effects of exposure to particles. There’s a lot in there, but here’s the first paragraph of their conclusions in that chapter:

While the literature varies in scope and depth, overall the committee concludes that there is strong evidence that exposure to indoor PM2.5 has adverse effects on the respiratory and cardiovascular systems and likely other organ systems. Specifically, the epidemiologic evidence points to consistent dose–response relationships between indoor PM2.5 exposure and respiratory and cardiovascular outcomes, and this evidence combined with toxicologic evidence and bolstered by the vast outdoor PM2.5 literature directly implicates indoor PM2.5 as a cause of adverse respiratory and cardiovascular effects. Furthermore, evidence for a role of indoor PM2.5 in neurologic, metabolic, and reproductive outcomes is less well developed but emerging. The absence of evidence should not be interpreted as indoor PM2.5 not exerting adverse effects on other organ systems, and instead this gap in knowledge underscores the urgent need for more research. It can thus be concluded reducing PM2.5 exposure would have a significant public health benefit.

Advice for better IAQ

Reducing the particulate matter in your indoor air is a good thing. I’ve mentioned some of the ways to remove it already (ventilation and filtration), but of course the first measure you should take is to try to keep them out of your home in the first place. That’s source control, which is the first step in a layered approach to indoor air quality. You know: Don’t burn the grilled cheese. Don’t run gasoline-powered equipment inside your home if there are other options. Or, as Joe Lstiburek says, just don’t do stupid stuff.

When the particle count goes through the roof as it has at our house this year, throw as much ventilation and filtration as you can at it. Keep that PM low, and you’ll breathe easier.

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Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and is the author of a bestselling book on building science. He also writes the Energy Vanguard Blog. For more updates, you can follow Allison on LinkedIn and subscribe to Energy Vanguard’s weekly newsletter and YouTube channel. Photos courtesy of author.