4.0 Ozone Attainment Test

Section 3 contained the details of the modeled attainment test that are common to both

ozone and PM2.5. This section describes several additional details related to the 8-hour ozone

attainment test. The section concludes with an example calculation.

4.1 Limiting modeled 8-hour daily maxima chosen to calculate RRF.

On any given modeled day, meteorological conditions may not be similar to those

leading to high concentrations (i.e., values near the site-specific design value) at a particular

monitor. If ozone predicted near a monitor on a particular day is much less than the design

value, the model predictions for that day could be unresponsive to controls (e.g., the location

could be upwind from most of the emissions in the nonattainment area on that day). Using

equation (3.1) could then lead to an erroneously high projection of the future design value.

In order to examine this issue, we analyzed modeled baseline and future emissions for 30

episode days during 1995 using a grid with 12 km x 12 km cells and 9 vertical layers29. We

examined modeled RRF’s computed near each of 299 monitoring sites in the eastern half of the

United States (Timin, 2005b). The study examined the day to day variability of (daily) RRFs at

each site. One purpose of the study was to assess the extent to which a relative response factor

(RRF) is dependent on the magnitude of modeled current 8-hour daily maxima.

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