Why is accurate flow verification essential for PM samplers?

• A. It is only necessary for calibration gas responses.
• B. It prevents filter contamination.
• C. It ensures mass concentration calculation relies on precise volumetric flow; flow errors bias results.
• D. It has no impact on results.

Answer: (C)

Accurate flow verification matters because PM mass concentration is calculated from the amount of mass collected on a filter divided by the volume of air drawn through the sampler. The volume equals the flow rate times the sampling time, so any error in the flow rate directly creates an error in the calculated concentration. If the flow is higher than intended, you sample more air and overestimate concentration; if it’s lower, you underestimate it. Keeping the flow within specified tolerances ensures the volume used in the calculation is correct, preventing biased results. This focus on the math of the concentration calculation is why flow verification is essential.