What is the function of a calibrated pump in active air sampling, and what common tolerance is expected for flow rate?

• A. The pump drives known air volumes through the sampler; typical tolerance is ±5–10% of the target flow rate.
• B. The pump filters contaminants; tolerance ±20%.
• C. The pump stores data; tolerance ±1%.
• D. The pump calibrates sensors automatically; tolerance ±50%.

Answer: (A)

In active air sampling, the essential function of a calibrated pump is to pull a known volume of air through the sampler over a defined period. Because the pump’s flow is calibrated to a target rate, the actual air volume drawn is predictable, which lets you relate the amount collected to an air concentration (for example, particles per cubic meter). If the flow is off, the collected volume won’t match the intended value, introducing error into concentration calculations and compromising comparability between samples. That’s why calibration and maintaining a specified flow rate are crucial.

The typical tolerance for the flow rate is about ±5–10% of the target value. This means the pump’s actual flow should fall within five to ten percent of the intended rate, balancing accuracy with practical operation. For instance, at a target of 2 L/min, an acceptable range would be roughly 1.9–2.1 L/min (±5%) or 1.8–2.2 L/min (±10%), depending on the method requirements.

The other options describe roles the pump doesn’t perform in active sampling: filtering contaminants, storing data, or automatically calibrating sensors.