FRM vs. FEM

The following definitions are taken from the US Code of Federal Regulations, Title 40, Part 50: (40CFR § 50.1)

Reference Method means a method of sampling and analyzing the ambient air for an air pMllutant that is specified as a reference method in an appendix to this part, or a method that has been designated as a reference method in accordance with part 53 of this chapter; it does not include a method for which a reference method designation has been cancelled in accordance with §53.11 or §53.16 of this chapter.

Equivalent Method means a method of sampling and analyzing the ambient air for an air pollutant that has been designated as an equivalent method in accordance with part 53 of this chapter; it does not include a method for which an equivalent method designation has been cancelled in accordance with §53.11 or §53.16 of this chapter.

The EPA has defined reference methods “FRM” for the measurement of various criteria pollutants, such as carbon monoxide, ozone, nitrogen dioxide, PM₁₀ and PM_2.5. These methods are described in great detail in the various appendices in 40CFR §50. For PM₁₀ and PM_2.5, the reference methods are both based upon manual sampling techniques where a pre-weighed filter is installed into a sampling device, ambient air is sampled for 24 hours, the filter is retrieved, equilibrated and then reweighed in order to produce the result. Only the measurement techniques defined in the various appendices in 40CFR §50 can be reference methods.

The EPA allows the use of equivalent methods as well for air quality surveillance. A federal equivalent method “FEM” is any measurement method that has been demonstrated by rigorous field tests in accordance with 40CFR §53 and adherence to the regulations in 40CFR §53 to produce equivalent results to the reference method. Such devices can be based on any measurement principle so long as it can be demonstrated to the EPA’s satisfaction that they produce “equivalent” data to the FRM.

The Met One BAM-1020 is an FEM for PM₁₀, PM_2.5 and  PM_10-2.5. It is the only monitoring method to simultaneously hold all three designations.

An FEM has been legally determined to be “equivalent” to the reference method. In most cases, the data produced by an FEM is treated the same way as the data produced by an FRM. In many cases, the FEM is actually preferable to the FRM. In the instance of the BAM-1020 vs. the FRM, the BAM-1020 could be considered preferable to the FRM because it automatically and continuously produces data where the FRM must be operated manually and does not produce its data in real time.