This procedure is repeated for each PM2.5 site and quarter to complete the calculation of
current ( baseline) ambient concentrations used as the basis for future estimates of PM2.5 mass
and its components.
46If there are less than 5 years of speciation data, then an assumption of
representativeness needs to be made. It is generally assumed that the inter-annual variability of
the species fractions is small compared to the variability of species concentrations. In the near
future, 5 full years of concurrent FRM and speciation data will be available.
(6) Modeled results show the following relative response factors (RRF) in predicted mass of 5
components of PM2.5 for the 3rd quarter:
(7) The quarterly mean RRFs from table 5.5 are multiplied by the weighted quarterly average
species concentrations from table 5.4 to derive future year concentrations.
From the example above, the future year 3rd quarter concentrations are:
SulfateFuture = 7.64 * 0.876 = 6.69 ug/m3
NitrateFuture= 0.99 * 0.943 = 0.93 ug/m3
Organic carbon massFuture= 4.67 * 0.971 = 4.53 ug/m3
Elemental CarbonFuture= 0.81 * 0.932 = 0.75 ug/m3
OPPFuture= 0.63 * 1.042 = 0.66 ug/m3
(8) The future year concentrations derived in step 5 are used to calculate the future year
concentration of ammonium (if the direct ammonium RRF is not used) and particle bound water.
The future year ammonium concentrations are calculated from the sulfate, nitrate, and
(current year) DON values. Assuming that the DON is unchanged from the current year47, the
ammonium is calculated using the following formula:
NH4future = DON * SO4future + 0.29*NO3future,
In the example above, assuming the base year DON is 0.336,
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