What is the difference between PM2.5 and PM10 with respect to the atmospheric pollutants?

The difference between PM10 and PM2.5 is size. “PM” refers to particulate matter—particles in the air. Those particles are things like organic dust, airborne bacteria, construction dust, and coal particles from power plants (for example, check out this study from researchers in Shanghai who analyzed what those particles are really made of).


Now on to size. The “10” and the “2.5” refer to microns (AKA micrometers). Microns are tiny. Here’s an idea of how small microns are compared to human hair:


Next, there’s a hidden (unlabelled) detail in the terms “PM10” and “PM2.5.” That is the “smaller than” piece. Each pollutant type is defined as that size and below. So PM 10 is particles 10 microns and below. PM2.5 is 2.5 microns and below. (That means PM 10 includes PM 2.5.)


What PM is not

Finally, it’s helpful to think of what PM is not. Particulate pollution does not include gas pollutants like ozone and NO2.

For fellow nerds curious to read more about PM 2.5:

  1. I describe how governments measure PM 2.5 here (including the trick of how they get rid of any particles in the air larger than 2.5 microns)
  2. I describe what PM 2.5 does to our bodies in this answer.
  3. In this answer, I detect PM 2.5 in my home in Beijing and test whether a simple DIY air purifier I made can clean it up.

Hope this helps!

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