What’s the difference between PM2.5 and PM10?

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According to my laser particle counter, the number of particles in t he 2.5 micron size range is typically in the 10-90 thousand per cubic meter (in a non-smoggy city) compared with 10 times that number for the 1 micron size range and 10 times that number again for the 0.3 micron size range. ( I could not find comparable data from the EPA because their measurements are in weight measures). All of these represent perhaps one percent of particulates, most of which are below 0.1 micron. Thus, it would appear that the molecular nature of the 2.5s is a… Read more »


The following statement is made in the article: “…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.)…” It seems more intuitive that a filter for PM10 filters particles down to 10 microns, and a PM2.5 filters particles down to 2.5. If this is correct filter for PM2.5 will also filter out PM10, but a PM10 filter will not filter out particles PM2.5, which are smaller than PM10? Another way of reading… Read more »


Ok, I found this paper which gives the following definition: (Taken from the 2016 paper: “Beyond PM2.5: The role of ultrafine particles on adverse health effects of air pollution”) “Generally, airborne particles can be defined as ambient airborne particulate matter (PM) which is grouped as coarse, fine, and ultrafine particles (UFPs) with aerodynamic diameters within 2.5 to 10 μm (PM10), below-2.5 μm (PM2.5), and below-0.1 μm (PM0.1), respectively.” Btw, from this paper, I was disturbed to learn the following: “The association of adverse effects on human health with PM10, PM2.5 or PM0.5 exposure had been well described [105–110]. However, increasing… Read more »


If PM10 particles are defined as particles with a diameter below 10 microns, does a PM10 reading also include the PM2.5 fraction (because PM2.5 is lower than 10 microns…)? the fact that PM2.5 can sometimes be higher than PM10 suggest that PM10 are not just particles below 10 microns, rather probably particles below 10 microns and *above* 2.5 microns… Is this right?