PM2.5 and PM10 are the two types of air pollution that the WHO estimates affect “more people than any other pollutant,” but they are different. Here’s how the two contrast.
PM2.5 vs. PM10
The difference between PM10 and PM2.5 is size. But before we get to 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.
Read more: If you’re curious what particles we’re breathing in polluted cities, check out.
Does Size Matter?
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 PM10 is particles 10 microns and below. PM2.5 is 2.5 microns and below. (That means PM10 includes PM2.5.)
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. It also doesn’t include gas pollutants that often come from inside our home, such as formaldehyde off-gassing from new furniture.
For fellow nerds curious to read more about particulate pollution:
- I describe (including the trick of how they get rid of any particles in the air larger than 2.5 microns).
- I describe and .
- In , I detect 2.5 micron particles in my home in Beijing and test whether a simple I made can clean it up.
Thomas is an Associate Professor of Behavior Science at the University of Chicago Booth School of Business and the founder of Smart Air, a social enterprise to help people across the world breathe clean air without shelling out thousands of dollars for expensive purifiers.