11.1 What Is A “Conceptual Description”?
A “conceptual description” is a qualitative way of characterizing the nature of an area’s
nonattainment or regional haze problem. It is best described by identifying key components of a
description. Examples are listed below. There are 3 different examples. One each for ozone,
PM2.5, and regional haze. The examples are not comprehensive. There could be other features of
an area’s problem which are important in particular cases. For purposes of illustration later in
the discussion, we have answered each of the questions posed below. Our responses appear in
11.1.1 8-Hour Ozone NAAQS
1. Is the nonattainment problem primarily a local one, or are regional factors important?
(Surface measurements suggest transport of ozone close to 84 ppb is likely. There
are some other nonattainment areas not too far distant.)
2. Are ozone and/or precursor concentrations aloft also high?
(There are no such measurements.)
3. Do violations of the NAAQS occur at several monitoring sites throughout the
nonattainment area, or are they confined to one or a small number of sites in proximity to
(Violations occur at a limited number of sites, located throughout the area.)
4. Do observed 8-hour daily maximum ozone concentrations exceed 84 ppb frequently or
just on a few occasions?
(This varies among the monitors from 4 times up to 12 times per year.)
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