(FRM) (EPA, 1997a) derived PM2.5 by the monitored fractional composition of PM2.5 species for

each quarter. (e.g., 20% sulfate x 15.0 ug/m3 PM2.5 = 3.0 ug/m3 sulfate).

Step 2. Using model results, derive component-specific relative response factors (RRF) at

each monitor for each quarter.

For each quarter, apply an air quality model to estimate current and future concentrations for

each of the components of PM2.5. Take the ratio of future to current predictions for each

component. The result is a component-specific relative response factor (RRF).

The relative response factor for component j at a site i is given by the following expression:

(RRF)ij = ([Cj, projected]/[Cj, current])i

where Cj, current is the quarterly mean concentration predicted at or near the monitoring site

with emissions characteristic of the period used to calculate the baseline design value for

annual PM2.5.

Cj, projected is the future year quarterly mean concentration predicted at or near the

monitoring site.

(e.g., given model predicted base year sulfate of 10.0 ug/m3 and future year concentration of 8.0

ug/m3, then RRF for sulfate is 0.800).

Step 3. Apply the component specific RRFs to observed air quality to obtain projected

quarterly species estimates.

For each quarter, multiply the current quarterly mean component concentration (step 1) times the

component-specific RRF obtained in step 2. This leads to an estimated future quarterly mean

concentration for each component. (e.g., 3.0 ug/m3 sulfate x 0.800 = future sulfate of 2.4 ug/m3).

Step 4. Calculate a future year annual average PM2.5 estimate.

Sum the quarterly mean components to get quarterly mean PM2.5 values. Then average the

quarterly mean PM2.5 concentrations to get a future year annual average PM2.5 estimate for each

FRM site.

Compare the projected average annual arithmetic mean PM2.5 concentration obtained in Step 4

with 15.0 :g/m3. If all values are < 15.0 :g/m3, the test is passed.

5.1.1 What Ambient PM2.5 Data is Used in the Attainment Test?

PM2.5 data collected at FRM sites is used for nonattainment designations. Therefore we

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