Which Indoor Air Pollutants Matter Most?
That face above is of a physician, alchemist, and astrologer named Philippus Aureolus Theophrastus Bombastus von Hohenheim. He is deemed the father of toxicology and is better known by the name Paracelsus. I begin this article with him because Dr. Brett Singer, at Building Science Summer Camp this year, used an interesting Paracelsus quote:
"Poison is in everything, and no thing is without poison. The dosage makes it either a poison or a remedy."
The pollutants in your indoor air
I wrote about Singer's mention of the Corsi Code in August and his kitchen ventilation data last month, but his presentation covered more than those two things. He began with a look at some of the various indoor air pollutants and and which ones we ought to worry more about. Here's his list of the biggies:
- Particulate matter
- Secondhand smoke from cigarettes (SHS)
- Nitrogen dioxide (NO2)
- Carbon monoxide (CO)
- Ozone (O3)
- Gas-phase organics (a.k.a., volatile organic compounds, or VOCs)
- Bioeffluents (including carbon dioxide)
Of course, if we wanted a full list of every individual pollutant, we'd have to expand this list quite a bit. VOCs, for example, include a wide range of different chemicals: formaldehyde, benzene, acrolein, and more. And, according to the Centers for Disease Control (CDC), "tobacco smoke contains more than 7,000 chemicals, including hundreds that are toxic and about 70 that can cause cancer."
OK, so which of those should we worry about the most? Which should we focus our efforts on minimizing?
Singer had a slide for that. In terms of a quantity called Disability Adjusted Life Year (DALY), he presented a graph of the health impact per year per 100,000 people. Here it is.
What do these numbers mean?
Note that the scale of the graph changes by powers of ten. Near the bottom of the list, chromium is sitting at about 10-1, or 0.1. At the top is PM2.5 at about 103, or 1,000. Clearly then, PM2.5 deserves a lot more attention than chromium. In fact, it looks like it deserves more attention than pretty much anything else on the graph.
The rankings in this chart, though, are based on averages over the whole population included in the studies. You can't look at that chart and say that every household will be affected the same way. PM2.5 may be at the top, but in a house where someone smokes indoors, secondhand smoke is most likely your biggest risk. Likewise with the other pollutants.
Another factor to consider is that not everyone reacts the same way to these pollutants. Most of the impact is felt by sensitive populations, like people with asthma, the elderly, or those with other existing health problems.
What you can do to improve your indoor air quality
Thinking about improving your indoor air quality in the abstract is all well and good, but it helps when you have a chart like the one above. Here's my short list of recommendations:
1. PM2.5. First, always run your kitchen range hood and bath fans whenever you're doing anything that might generate particulate matter. Second, filter the outdoor air you bring in through a mechanical ventilation system and filter the indoor air. (I've got some articles on filtering the air coming soon, so stay tuned.)
2. Secondhand smoke. Don't allow smoking in the house. Simple, right?
3. Mold and moisture. Address any moisture problems in the house to make sure things stay dry and that they can dry out when they get wet. This is one of the biggest issues in building science because moisture causes a lot of problems.
4. Radon. Get a radon test. Get your home remediated for radon if the results show too high a radon level. Radon is the second-leading cause of lung cancer.
5. NO2. Don't use unvented combustion appliances. Yeah, that nice-looking ventless gas log fireplace could be making you sick.
6. Carbon monoxide. Get a low-level CO monitor. I can't say this often enough. The standard UL-rated CO detectors won't give you an alert until the level is dangerously high, like 70 parts per million (ppm) for a couple of hours. But you could have 60 ppm for days on end with no idea that you're being poisoned.
7. VOCs and other chemicals. Source control. As much as possible, pay attention to the materials you bring into the home. Don't know enough? Go to the Six Classes website. Then use mechanical ventilation to dilute what you do get.
There's nothing inherently difficult about changing an existing home to improve the indoor air quality or building a new home that will have good IAQ from the beginning. The devil, as always, is in the details.
Now that you know which indoor air pollutants might have the biggest impact on your health, you can craft a strategy to reduce their concentrations from the poison level to something more benign. I don't recommend trying to turn PM2.5 or radon into a remedy, but, unlike Paracelsus, I'm not an alchemist.
Image of Paracelsus from the Wellcome Collection, used under a Creative Commons license.
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