Indoor Air Quality – Particulate Matter

It’s a Tough Problem

As I am sure you can imagine, Indoor Air Quality (IAQ) on a submarine is essential to survival. What’s the big deal? Just make oxygen. Isn’t pure oxygen highly flammable? What do you do with all the carbon dioxide? What about the hazards associated with the chemical that is needed to remove carbon dioxide? It’s the ultimate dichotomy. Every problem you solve creates a new problem. It is a complex engineering task. Expensive equipment with extremely strict operating guidelines is in place to ensure the air is breathable and safe. After you’ve solved all the problems, we still have backups like emergency breathing air. Even after that, we prepare the crew for what to do when it all just stops working. So now surely, we’ve done enough. No. One more thing. We have a list: things you can’t bring onboard at all; things you can bring onboard but just in small amounts. 

“Can I bring a sleeping bag? It would be really handy when I’m hot racking.”

“Nope, when a sleeping bag burns it gives off a dangerous chemical.” 

“Give me a break. All of this stuff in place and I can’t have a sleeping bag?”

The point is, Indoor Air Quality is a tough problem to solve. Although to a much lesser extent, it’s a tough problem even in your home. Even if you buy every product that exists, you are still going to have some inefficiencies and decisions to make. Most homeowners probably want to just focus on solving their worst problem with the best solution. Fortunately for homeowners, the worst problem might be the easiest to solve.

Fine Particulate Matter


Particulate matter is the #1 health risk factor in Indoor Air Quality. Studies have shown that it is a higher risk factor than secondhand smoke, a sedentary lifestyle, or being overweight. The top concern of the day is a virus. Viruses do not move around in the air naked. They are embedded in particulate matter. So, it stands to reason. If I deal with particulate matter, I will also deal with viruses. 

Particulate matter (also referred to as PM or particle pollution) is a complex mixture of solid and/or liquid particles suspended in the air. PM is broken into three categories based on size: coarse (>2.5 microns), fine (0.1-2.5 microns), and ultrafine (<0.1 microns).

Particulate matter in pet dander, cockroaches, mites, molds, bacteria, and smoke


The smaller the particle, the more likely it is to be airborne and retained in the body if inhaled. But as you can see from the preceding graph, ultrafine particles primarily come from a combustion process, cooking, fireplaces, etc. However, most combustion PM is generally controlled at the source. The presence of smoke in your house is uncomfortable enough that only short-term exposure would be tolerated. I won’t spend time on it here. But it should be noted, that PM from cooking is a real problem. Most cooking hoods are ineffective and a very small percentage of people use them. Coarse PM is of sufficient size that most filtering processes remove it from the air and much of it winds up as dust. Fine PM is difficult to remove from the air, is easily suspended in the air, and creates a significant health risk. Also, because it concentrates indoors, it can be 2-5 times higher than outdoor PM levels.  

Strategies to Reduce

The Environmental Protection Agency (EPA) adopts three primary strategies to reduce indoor air pollutants:

  • Remove the Source
  • Ventilation
  • Air purification

Remove the Source

The strategy of removing the source is very effective. The source of chemical pollutants, volatile organic compounds, and mold can generally be identified and removed. However, the source of PM can be much more difficult to deal with emotionally. Our two Shih-Tzu puppies, Lily and Coco, are definite sources of PM. Oh, it’s true. They shed very little. But if how often my wife complains of mopping up dirty paw prints is any indication of how much PM they bring inside, they are practically bringing it in by the shovel fulls. At this point, however, the three children are much more likely to go than Lily and Coco. So, for now, I’ll have to find another way to deal with our PM.


Because PM tends to concentrate indoors, primarily due to indoor sources. The EPA recommends opening windows routinely to change out indoor air with fresh air. This represents a problem for many people. The weather is a factor. It is 28 degrees outside right now, and probably not opening any windows. Alternatively, I won’t be doing it when it’s 90 degrees either. There are only two short periods every year in the Spring and Fall when the weather cooperates with this strategy. However, those periods are the height of allergy season and can be dangerous for allergy sufferers. 

Engineered mechanical means exist to change out indoor air continuously and even as needed to control air pollutants. The two types are:

Both types can work with your existing HVAC system or independently. The applications for each are different. The ERV should be used in humid climates as it removes humidity from the air brought indoors. This is much safer and more convenient than opening your windows. The air that’s brought in is filtered and conditioned so the weather is not a factor. It also has the extra added benefit of helping to control humidity. 

Diagram of an Energy Recovery Ventilation system cycling air in and out of the home.

Air Purification

Air Purification is the least effective of the 3 strategies but is commonly adopted because of its convenience and ease of use. 95% of products are geared toward air purification. You can’t talk about air purification without talking about efficiency vs. effectiveness. There is a long, drawn-out explanation of this with graphs but I’ll attempt to sum it up in one sentence. A 99.9999999999% efficient filter if it existed is ineffective if no air is passing through it. It doesn’t matter how well a product works if it isn’t running. Air purification systems have to be designed with this in mind. For example, the EPA recommends using a MERV 13 filter. MERV is the Minimum Efficiency Reporting Value. They arrived at this number taking into account how much the typical home’s HVAC system runs. They balanced the efficiency of the filter with the expected usage to achieve an overall reduction in exposure to Indoor Air Pollutants or effectiveness. Check out the EPA’s Guide to Air Cleaners in the Home for more information.


I tend to favor the ERV as the best option. Benefits:

  • Reduces all Indoor Air Pollutants (PM, VOCs, Allergens) by as much as 500%
  • Changes out the stale indoor air with fresh air
  • Removes odors from pets and cooking
  • Most effective because it runs independently of your heating and air system
  • No loss of HVAC efficiency
  • Helps control humidity
  • Can be combined with IAQ monitors to control actual IAQ

It is by far the best return on investment.

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