In ambient air monitoring QA/QC, what is the purpose of calibration gas checks and related instrument verification?

• A. To correct for drift after data collection only.
• B. To adjust the instrument's altitude.
• C. To ensure accuracy of measurements by verifying analyte response with calibration gas and maintaining instrument performance between field audits.
• D. To change the instrument's sampling rate.

Answer: (C)

The idea being tested is how calibration gas checks validate that an ambient air monitor is actually measuring correctly and remains reliable over time. Calibration gas checks expose the instrument to a known concentration of a calibration gas and verify that the instrument’s response matches that known value. This process confirms the sensor’s current sensitivity, helps catch drift, leaks, contamination, or pump/flow issues, and ensures the instrument stays within specified performance between formal field audits. It’s about proactive verification to guarantee accurate measurements, not about adjusting altitude, changing the sampling rate, or correcting data after collection. That’s why this option—verifying analyte response with calibration gas and maintaining instrument performance between field audits—is the best choice.