What average particle diameters define the lower and upper particulate matter as a pollutant?

What average particle diameters define the lower and upper particulate matter as a pollutant?

• A. 0.5-1 um
• B. 1.5-7.5 um
• C. 2.5-10 um
• D. 10.5-20 um

Answer: (C)

Particulate matter is classified by how large the particles are, because size affects health and behavior in the air. The two main regulatory categories are PM2.5 (2.5 micrometers and smaller) and PM10 (up to 10 micrometers). The range that defines the coarse portion between these cutoffs is 2.5 to 10 micrometers, which is why this option best fits the idea of the lower and upper limits used to describe common PM pollutants. Other ranges don’t align with the standard size classifications: smaller than 2.5 μm misses the lower fine-particle cutoff, ranges that span both sides of the boundary aren’t the standard definitions, and larger ranges exceed the PM10 category.

Particulate matter is classified by how large the particles are, because size affects health and behavior in the air. The two main regulatory categories are PM2.5 (2.5 micrometers and smaller) and PM10 (up to 10 micrometers). The range that defines the coarse portion between these cutoffs is 2.5 to 10 micrometers, which is why this option best fits the idea of the lower and upper limits used to describe common PM pollutants. Other ranges don’t align with the standard size classifications: smaller than 2.5 μm misses the lower fine-particle cutoff, ranges that span both sides of the boundary aren’t the standard definitions, and larger ranges exceed the PM10 category.