Buying an Air Purifier to Combat Pollution

pollution air purifier

Are you buying an air purifier for pollution, for particulate matter, PM 2.5, PM10? What even is pollution in the home? Isn’t pollutive particulate matter just called dust when it’s inside the home? Let’s first take a look at what exactly it is that you’re trying to filter out of the air with an air purifier inside your home – assuming you’re looking for an air purifier for PM2.5, PM10, etc. - and then we’ll look at some specific model recommendations.

First a few definitions and distinctions need to be made


Pollution involves any type of contaminant being introduced into a particular environment. The contaminant can be anything from a substance (including particles) to a form of energy (like noise, heat, or light).

Particle pollution

Particle pollution is a specific type of pollution – pollution that involves particles.

Another name for particle pollution is Particulate Matter – PM for short. Instead of referring to this type of pollution as particle pollution, air quality experts simply call it PM.

Doing so allows them to easily attach a number to the end to describe exactly the type of particle pollution they may be referring to. For example, PM10 refers to particle pollution comprised of particles 10 microns and smaller. Clearly, it’s much easier to say “PM10” instead of “particle pollution comprised of particles 10 microns and smaller”.

Note that the particles comprising PM can be solids or liquids.

In terms of size, the particles can definitely be larger than 10 μm although the term “PM” is usually associated with particles smaller than 10 μm. The EPA calls these “particles of concern” as they can easily enter the lungs. Particles larger than 10 microns are less of a concern because they generally do not enter the lungs and only irritate the eyes, nose, and throat.

So, in summary, PM is

  • Pollutive
  • A liquid or a solid
  • Any size that is considered “particulate” but usually 10 microns and smaller


Dust is defined as “fine particles of solid matter”.  Nothing about this definition suggests that dust is necessarily a pollutant.

The definition does make it clear that we’re talking about solid matter so liquids are excluded when talking about dust.

The term “fine” is not very specific when it comes to size. Dust can comprise any size particles considered “fine” particles.

So, in summary, dust can be

  • Pollutive or non-pollutive
  • Only a solid
  • Any size that is considered “fine”

The bottom line here is that dust and PM are two very different things. We discuss dust and recommended air purifiers for dust here. For the rest of this guide, we’ll focus on PM and air purifiers for PM.

A closer look at PM

Recall that the EPA tends to associate PM with particles that are 10 μm in diameter or smaller. Particles this small can be further categorized as

Coarse particles

larger than 2.5 μm and smaller than, or equal to, 10 μm in diameter

Fine particles

2.5 μm in diameter or smaller

Ultrafine and nanoparticles

less than 0.1 μm in diameter

Recall the naming convention we talked about earlier – “PM” and then a number. Instead of using the terminology above (coarse, fine, etc.), the far more common but slightly less specific way to describe these particles is:


this includes all particles above (all particles 10 μm or smaller) – coarse, fine, and ultrafine particles


this includes only coarse particles (particles between 2.5 and 10 μm in diameter)


this includes fine particles and ultrafine particles (particles 2.5 μm and smaller)

Finally, we can also categorize these particles by source:

Primary particles

release directly from a source (e.g. a construction site or smokestack)

Secondary particles

form in complex chemical reactions in the atmosphere

What exactly is PM made of?

Most of the fine particle pollution (PM2.5) in the US is comprised of secondary particles (as defined above). In other words, most of the PM2.5 pollution in the US is comprised of particles that are the result of chemical reactions that take place in the atmosphere. The source of these chemicals? Emissions from power plants, factories (industry) and automobiles.

PM, in general (meaning all sizes – not just PM2.5), may consist of

  • Acids
  • Inorganic chemicals
  • Organic chemicals
  • Metals
  • Dust
  • Pollen
  • Mold
  • And more

But understand that PM2.5 is primarily the result of chemical reactions. These are not particles that originate at one source and then travel through the air untouched. They primarily enter the atmosphere where some type of chemical reaction takes place that transforms them into an altogether different type of particle.

What makes PM so problematic?

In a word – its size.

Because PM is so small (10 microns or less in diameter)…

  • It’s difficult to identify

    There doesn’t have to be visible haze or smoke in the area you live for there to be a substantial concentration of PM in the air. These particles are very small – small enough for you not to be able to see them with the naked eye.

  • It can stay airborne for a long time – this allows it to...
    • move from one area to another quite easily

      This means that even if you live relatively far away from primary and secondary particle sources you’re not necessarily in the clear when it comes to particle pollution.

    • be something you can possibly breathe in long after it’s originally emitted
  • It can easily penetrate your home.

    You don’t need to have your windows open 24 hours a day, 7 days a week for PM to enter your home. For example, PM can easily enter through gaps in doors and windows, chimneys, and of course even when you open your front door to leave or come into your home.

The real problem

The smaller the PM, the more all of the above points are true – the more difficult it is to identify, the more easily it can travel from one area to another, the longer it can stay airborne for you to breathe it in, and the more easily it can penetrate your home.

In other words, the smaller the PM,  the greater your likelihood of breathing it in – of being affected by it.

But here’s where things get really problematic.

As PM gets smaller it also becomes a much greater risk to your health.

Particles larger than 10 μm generally will NOT enter your lungs. They can still irritate your eyes, nose, and throat but they will not enter your lungs.

Particles between 2.5 μm and 10 μm will enter your lungs but won’t penetrate very deeply. They tend to deposit in the large airways of your lungs.

Particles 2.5 μm and smaller penetrate all the way to small peripheral airways and most importantly, to the alveoli where they can possibly enter the bloodstream. Because they penetrate so deeply, these PM2.5 particles are the worst offenders when it comes to your health.

How bad is it? The World Health Organization (WHO) cites studies that show that exposure to PM2.5 accounts for up 3.1 million deaths per year. They also cite studies that show that PM2.5 can reduce life expectancy by as much as 8.6 months on average.

Concentration thresholds

Furthermore, the WHO states that, when it comes to PM10 and PM2.5, there is “no evidence of a safe level of exposure or a threshold below which no adverse health effects occur.” This means that, according to the WHO, there’s no way to know for sure whether or not even low concentrations of PM can affect your health in a negative way.

Other governing bodies do give concrete thresholds, although no guarantee is made that concentrations lower than these will not affect your health in an adverse way.

The EPA gives the following national air quality standards:

For a 24 hour period….
The PM2.5 standard is 35 μg/m3 
The PM10 standard is 150 μg/m3

For a full year – prolonged exposure…
The PM2.5 standard at 12 μg/m3
There is no PM10 standard – it was revoked in 2006 “because of a lack of evidence establishing a link between long-term exposure to coarse particles and health problems”

Any measured concentration ABOVE these standards means air quality is a problem.

Note how the concentrations for short term exposure are much higher than concentrations given for long term exposure. This simply means that, according to the EPA, your body is able to withstand a higher concentration of PM as long as it’s over a short period of time. The prolonged exposure threshold is lower because the EPA believes that you cannot tolerate the same concentration levels over a long period of time. Makes sense.

The European union gives these standards:

For a 24 hour period….
The PM2.5 standard is not given
The PM10 standard is 50 μg/m3

For a full year – prolonged exposure…
The PM2.5 standard is 25 μg/m3
The PM10 standard is 40 μg/m3

Note how the EU believes that higher PM2.5 concentration is tolerable over a prolonged period of time as compared to the US. However, they also believe that a certain PM10 standard over a prolonged period is necessary while the US does not.

NOTE: The standards above do not take into account particulate matter larger than 10 microns. There are plenty of particles in the air that are this size and that can still potentially cause health issues or at the very least discomfort. See our guides on dust, mold, and pollen for some good examples.

Air Quality in the US

Looking at a map of the United States, much of the country meets or exceeds these standards – in other words, is below the EPA threshold for PM2.5 over a prolonged period of time.

However, understand that national and even state specific air quality maps and tools do not give you information relating to your specific neighborhood and the air inside your specific home.

If you do have a concern for particle pollution – if you live near an industrial area, if you exhibit certain symptoms indicative of breathing in poor quality air, or if you’re just generally concerned – we recommend you purchase an air quality monitor to determine the air quality inside your home.

A particle meter like the Dylos DC1100 Pro is normally recommended for such a task. The Dylos is simply the most accurate best value monitor available on the market.  

Improving Air Quality with an Air Purifier

Most air purifiers are equipped with

  • a carbon filter for gas filtration
  • a separate HEPA filter for particle filtration

Particulate Matter - PM2.5, PM10, and PM10+ - is comprised of solid (and liquid) particles. Thus, the air purifier’s HEPA filter is the only filter that does any work to reduce PM concentration in a room. The carbon filter only reduces the concentration of unwanted gases – like VOCs or odors.

Most air purifiers on the market are equipped with a HEPA filter. Thus, most air purifiers are well equipped to be able to reduce PM concentration in a room.

However, their efficacy varies according to one additional variable – CFM.

You see, HEPA filters remove particles from the air extremely efficiently – at an efficiency rating of 99.97%. That means that for every 10,000 particles that travel through the filter, only 3 make it through. The other 9,997 are successfully capture by the filter.

So HEPA filters are extremely efficient. But in order to actually be able to be efficient – for them to be able to process air - they need access to the air. The level of access can best be described in terms of CFM.

An air purifier’s CFM is the cubic feet of air it’s able to process – it’s able to pull into the air purifier, through the filter, and out of its outlet - every minute. The higher the CFM, the greater the filter’s access to air - the greater quantity or volume of air it can access (it can process) - every minute.

Generally, the higher the CFM the better, although our testing has shown that 250 CFM units, specifically, offer the best combination of value, energy efficiency, noise output, and versatility.

Beyond 250 CFM, units tend to be exorbitantly priced.

Below 250 CFM, units tend to not be as good a value, not as energy efficient, not as quiet (at equal output), and are also not as versatile – they can and should only be used in smaller rooms. 250 CFM units can very effectively lower both PM10 and PM2.5 in smaller rooms (150 sq. ft. and less) and larger rooms (up to 300 sq. ft.) alike.

In a small space (smaller than 150 sq. ft.) you can run 250 CFM units on lower settings for greater energy efficiency and lower noise output. Even on these lower settings, 250 CFM units will still be able to effectively reduce PM concentration in the room.

In a larger space up to 300 sq. ft. you will need to mostly run them on their highest fan speed for them to effectively reduce and establish a low PM concentration in the room, although you may be able to run them on a lower setting periodically (for a few hours here and there) to maintain that concentration.

And in a space larger than 300 sq. ft., multiple 250 CFM units are recommended over a single higher CFM unit, if only because it’s more cost effective to go about things in this way. In extra-large spaces we also recommend a particle meter to aid you in determining exactly how many units are required and what fan speeds to set them to in order to get the room to the PM concentration you desire.

Currently, the best 250 CFM unit on the market is the Winix 5500-2.

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