If volumetric flow errors occur during PM sampling, which quantity is biased?

• A. The sampling duration.
• B. The device serial number.
• C. The mass concentration calculation.
• D. The color of the filter.

Answer: (C)

Volumetric flow accuracy matters because the mass concentration reported for PM is calculated from the mass collected on the filter divided by the volume of air that passed through the sampler. If the flow rate is biased, the volume estimate is incorrect, so the mass concentration becomes biased as a result. The sampling duration is set by a timer and is not the quantity being directly calculated from the flow in this context, and the device serial number or the filter color are identifiers or physical attributes that do not affect the mass-per-volume calculation.