Which maintenance activity is used to ensure accurate sample flow through the PM monitor?

• A. Clean the enclosure daily.
• B. Change the filter weekly.
• C. Flow calibration.
• D. Replace the data logger.

Answer: (C)

The key idea is that the accuracy of PM measurements depends on sampling the correct volume of air. Flow calibration directly checks and adjusts the actual air flow to match the specified target. By using a calibrated flow reference in the sampling line, you verify that the pump and flow path are delivering the intended rate and you fine-tune them if they drift. This keeps the volume of air (and therefore the mass concentration calculation) correct over time, which is essential for reliable results.

Other routine maintenance like cleaning the enclosure, changing filters, or replacing the data logger keeps the instrument healthy or up-to-date, but they don’t specifically verify or correct how much air is being drawn through the monitor.