-and passively collected mass
To apply the test, States must first have run an air quality model at least twice--to
simulate current emissions and to simulate future year emissions. We recommend a modeled
attainment test which has 4 basic steps. Additional details are provided later in this section.
Step 1. Computeobserved quarterly mean PM2.5 and quarterly mean composition for each
Derive current quarterly mean concentrations37 for each of the major components of PM2.5. This
is done by multiplying the monitored quarterly mean concentration of Federal Reference Method
37Concentrations should be calculated based on calendar quarters for two reasons. First,
the NAAQS is calculated for a calendar year, so the quarters need to fit evenly within a year.
Second, the monitored data used to calculate design values is averaged on a calendar quarter
basis before calculating annual averages.
(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-specificrelative 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
Cj, projected is the future year quarterly mean concentration predicted at or near the
(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
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castellano: DIS CUS DES RAD english: DIS CUS DES RAD
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