Why is pump calibration critical in active air sampling?

• A. To ensure accurate flow rate and correct mass collected for concentration calculation.
• B. To prevent corrosion of sampling pumps.
• C. To calibrate the detector's sensitivity to light.
• D. To ensure the pump stops when sampling for too long.

Answer: (A)

In active air sampling, the concentration of a contaminant is calculated from the mass collected on the filter divided by the volume of air drawn through the sampler. Pump calibration is essential because it ensures the flow rate used to compute that volume is accurate. If the pump isn’t calibrated, the actual air volume could be higher or lower than assumed, biasing the concentration result. A higher-than-true flow rate makes the volume larger and the calculated concentration appear lower, while a lower-than-true flow rate makes the volume smaller and the concentration appear higher. Calibrating the pump keeps the volume measurement reliable, supports consistent sampling, and improves the accuracy of exposure assessments. The other options don’t address how the volume—and thus the concentration calculation—depends on the actual flow through the pump.