The FRM data is used to determine compliance with the NAAQS. Therefore, it is critical

to estimate the species composition as measured on the FRM filters. In addition, for the

purposes of predicting changes in PM2.5 components, constructed PM2.5 mass should match the

composition of mass retained by the FRM. As such, we are recommending changes to the

calculation and definition of PM2.5 species compared to the (original 2001) draft PM2.5 modeling


We recommend a SMAT technique which uses an FRM mass construction methodology

which results in reduced nitrates (relative to the amount measured by routine speciation

networks), higher mass associated with sulfates and nitrates (reflecting water included in

gravimetric FRM measurements) and a measure of organic carbonaceous mass which is derived

from the difference between measured PM2.5 and its non-organic carbon components (Frank,


40The information in this section applies to the most common samplers in the STN

network. Some networks use alternative special purpose samplers to collect both PM2.5 and

PM2.5 speciation data. The characteristics of the sampler and the analytical procedures used to

produce chemical speciation data should be considered in determining which, if any adjustments

are appropriate to make the data useful for comparison to FRM data.

41The draft PM2.5 modeling guidance recommended a mass reconstruction scheme that

was identical to the IMPROVE technique. We are still recommending use of IMPROVE

assumptions for regional haze modeling (see section 6).


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