Which statement best describes the typical collocation requirement for PM2.5 SLAMS?

• A. Collocation applies only to PM10.
• B. A collocated monitor must be operated with the primary monitor for a defined period to estimate bias and precision.
• C. Collocated monitors are optional and not compared.
• D. Collocation is performed after data submission.

Answer: (B)

During PM2.5 SLAMS QA, you run a collocated monitor alongside the primary PM2.5 monitor for a defined period. This setup lets you directly compare simultaneous measurements to estimate bias (the systematic difference between the two instruments) and precision (how consistently they agree). This process ensures the PM2.5 data from the primary monitor reflect true concentrations within the expected measurement performance. It isn’t limited to PM10, it isn’t optional, and it isn’t done after data submission—the collocation period occurs during data collection to validate and quantify measurement accuracy.