What distinguishes primary data from backup data in QA/QC documentation?

• A. Backup data are derived results; primary data are raw instrument signals.
• B. Primary data are metadata; backup data are actual measurements.
• C. Primary data are the actual measurements; backup data include metadata, calibration records, field notes, QAQC outcomes supporting data validity.
• D. Backup data are the raw instrument signals; primary data are processed results.

Answer: (C)

In QA/QC documentation, the actual measurements recorded by the instrument during sampling and analysis are the primary data. They are the values you would analyze and report to characterize air quality. The backup data are the supporting information that proves those measurements are valid and traceable: metadata about the sampling event (when, where, how it was collected), calibration records and instrument maintenance logs, field notes describing conditions that could affect results, and QA/QC outcomes such as blanks, standards, duplicates, and performance checks. Together, they create a clear trail from the measurement to the reported result, making it possible to verify accuracy, reproduce analyses, or investigate any anomalies. For example, if a NO2 concentration is reported, the primary data are that concentration value, while the backup data include the calibration curve used, the instrument’s status at the time, the sampling location, and QA/QC results that support the data’s validity.