Discussion
Consider the following statements about particulate matter:
1. PM2.5 is defined by aerodynamic diameter below 2.5 micrometres.
2. Fine particles penetrate to the alveolar region.
3. Coarse particles have the longer atmospheric residence time.
Which of the statements given above is or are correct?
Answer: C
Correct answer: 1 and 2 only
Statement 1 is correct: PM2.5 is the fraction with aerodynamic diameter below 2.5 micrometres. Statement 2 is correct: fine particles penetrate to the alveolar region, which is why they drive the cardiopulmonary effects.
Statement 3 is false and reverses the comparison. Fine particles have the longer residence time - days to weeks - because they are too small to settle appreciably and too large to coagulate quickly. Coarse particles settle out within hours to days, which is why fine particulate is a regional problem and coarse particulate a local one.
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