PM10 particles are at most how many micrometers in diameter?

• A. 10 micrometers or smaller
• B. 20 micrometers or smaller
• C. 15 micrometers or smaller
• D. 5 micrometers or smaller

Answer: (D)

PM10 refers to particles with an aerodynamic diameter of 10 micrometers or smaller. So the largest particle included in this category is 10 μm, making the correct maximum diameter 10 micrometers. A choice of 5 μm or smaller would miss the particles that are between 5 and 10 μm, which are still PM10. Choices of 15 μm or 20 μm would include particles larger than the PM10 threshold and thus aren’t correct.