For areas which contain one or more speciation sites, and where FRM sites exhibit very
little spatial gradients, it may be appropriate to assume that the speciation site is representative of
the entire area. Areas which exhibit strong spatial gradients in PM2.5 concentrations should
strongly consider using more sophisticated techniques to estimate species concentrations.
Combining ambient data with model output concentrations (number 4 above) may help adjust
concentrations in areas with strong gradients, but limited speciation data. This technique has
great promise but has not been used extensively for PM2.5 analyses. The technique is further
limited by uncertainties in the representativeness of the model outputs and emissions inventories.
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.
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castellano: DIS CUS DES RAD english: DIS CUS DES RAD
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