5.1.3 New Species Calculations and Definitions

Recent data analyses (Frank, 2006) have noted that the FRM monitors do not measure the

same components and do not retain all of the PM2.5 that is measured by routine speciation

samplers and therefore cannot be directly compared to speciation measurements from the

Speciation Trends Network (STN)40. By design, the FRM mass measurement does not retain all

ammonium nitrate and other semi-volatile materials (negative sampling artifacts) and includes

particle bound water associated with sulfates, nitrates and other hygroscopic species (positive

sampling artifacts). This results in concentrations (and percent contributions to PM2.5 mass)

which may be different than the ambient levels of some PM2.5 chemical constituents.

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

guidance41.

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,

 

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