Which statement about PM10 and PM2.5 is accurate?

• A. PM10 is defined as up to 10 micrometers in diameter and PM2.5 as up to 2.5 micrometers.
• B. PM2.5 is larger than PM10.
• C. PM2.5 is never considered in indoor air quality assessments.
• D. PM10 particles are always smaller than PM1.

Answer: (A)

PM10 and PM2.5 are defined by specific size cutoffs: PM10 includes airborne particles with diameters up to 10 micrometers, while PM2.5 includes those up to 2.5 micrometers. Since 2.5 micrometers is smaller than 10, PM2.5 particles are within the PM10 range, so the statement that PM10 is defined up to 10 micrometers and PM2.5 up to 2.5 micrometers is accurate.

This distinction matters because particle size affects how deeply particles can penetrate the respiratory system and influence indoor air quality. Fine particles (PM2.5) pose different health considerations than the broader mix captured by PM10. The other options don’t fit these definitions: PM2.5 is not larger than PM10, PM2.5 is indeed considered in indoor air quality, and PM10 includes particles larger than PM1, not smaller.