Give an example of FRM PM2.5 and an EPA-approved FEM PM2.5 method.

• A. FRM PM2.5 uses gravimetric filter sampling (reference gravimetric method); an EPA-approved FEM PM2.5 could be a continuous mass monitor validated as equivalent to FRM.
• B. FRM PM2.5 uses optical scattering; FEM uses gravimetric.
• C. FRM PM2.5 uses gas chromatography; FEM uses ion chromatography.
• D. FRM PM2.5 is offline; FEM PM2.5 is online.

Answer: (A)

The idea being tested is how PM2.5 is measured under regulatory standards: the Federal Reference Method relies on a gravimetric approach, while the Federal Equivalent Method includes other methods that EPA has demonstrated to be equivalent to that reference.

For PM2.5, the reference method collects air on a size-selective filter and determines mass by weighing the filter before and after sampling (a gravimetric measurement). An EPA-approved FEM is a method that has undergone EPA evaluation and shown results that match the FRM’s accuracy, often a continuous mass monitor that has been validated as equivalent to FRM. So an example is using gravimetric filter sampling as the FRM, with a continuous mass monitor (validated as equivalent to FRM) as the FEM.

The other options misstate how FRM works (optical scattering or chromatography aren’t the FRM principles) or rely on an inaccurate distinction (offline vs online) that isn’t the defining criterion for FEM designation.