Premise PM4. Sampling anomalies associated with the Federal Reference Method for PM2.5

need to be considered as part of the model attainment demonstration. A NAAQS needs to

be related to observed health effects. In order to establish this link most clearly, the U.S. EPA

has adopted a Federal Reference Method (FRM) for measuring PM2.5 similar to procedures used

in epidemiological studies in which adverse health effects are associated with exposure to PM2.5

(40 CFR Part 50, Appendix L). Since the FRM is included in the definition of the NAAQS, the

modeled attainment test we recommend uses the measured concentrations of FRM PM2.5 as the

“ground truth”. The FRM sampling protocol is known to be a precise measurement, but it may

not accurately measure PM2.5 in the air. There are many known positive and negative sampling

artifacts associated with the measurement and analysis protocol. Among them are positive

artifacts associated with organics and water retained on the Teflon filter and negative artifacts

associated with volatile nitrates and organics (Frank, 2006).

The attainment test recommends using speciated ambient data to estimate PM2.5 components.

These measurements are from the Speciation and Trends Network (STN) for urban sites and the

Interagency Monitoring of PROtected Visual Environments (IMPROVE) network for Class I

areas. The Speciation measurements use different protocols than FRM measurements.

Therefore, the species measured by STN and IMPROVE are often not directly comparable to the

FRM PM2.5. The attainment test recommends a set of default procedures to adjust the speciation

measurements to make them more comparable to FRM measurements.

 

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