recommend using FRM data as the base data for projecting future PM2.5 concentrations. As can
be seen from the list of steps, the modeled attainment test is critically dependent on the
availability of species component mass at FRM sites. This raises several issues. First, the FRM
filter measurements and PM2.5 speciation measurements do not always measure the same mass
(Frank, 2006). There are numerous known issues with positive and negative sampling artifacts.
And second, the majority of FRM sites do not have co-located STN38 speciation samplers39.
Both of these issues are addressed below.
5.1.2 FRM Monitors that Don’t Have Speciation Data
There are approximately 1200 FRM sites and only ~200 urban speciation monitoring
sites. This makes it difficult to apply the attainment test at the majority of FRM sites. Species
concentration data and/or species fractions are needed in order to apply SMAT. There are
several possible ways to estimate species concentrations at FRM monitors that lack speciation
data. Among them are:
1) Use concurrent data from a nearby speciation monitor to estimate species concentrations
and/or fractions at one or more FRM sites.
2) Use representative speciation data (from a different time period) collected in an area to
estimates species data at FRM sites.
3) Use interpolation techniques to create spatial fields using ambient speciation data.
4) Use interpolation techniques to create spatial fields using ambient speciation data and gridded
model outputs to gradient adjust the species concentrations.
In general, we recommend using spatial interpolation techniques to estimate species
concentrations at FRM sites that do not have speciation data (numbers 3 and 4 above). But in
some cases, interpolating data from nearby sites may not be appropriate, may not be feasible, or
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