10. Have ambient precursor concentrations or measured VOC species profiles changed?

(There are no measurements.)

11. What past modeling has been performed and what do the results suggest?


(A regional modeling analysis has been performed. Two emission scenarios were modeled:

current emissions and a substantial reduction in NOx emissions throughout the regional

domain. Reduced NOx emissions led to substantial predicted reductions in 8-hour daily

maximum ozone in most locations, but changes near the most populated area in the

nonattainment area in question were small or nonexistent.)

12. Are there any distinctive meteorological measurements at the surface or aloft which

appear to coincide with occasions with 8-hour daily maxima greater than 84 ppb?

(Other than routine soundings taken twice per day, there are no measurements aloft. There

is no obvious correspondence with meteorological measurements other than daily maximum

temperatures are always > 85 F on these days.)

Using responses to the preceding questions in this example, it is possible to construct an

initial conceptual description of the nonattainment area’s ozone problem. First, responses to

questions 1 and 11 suggest there is a significant regional component to the area’s nonattainment

problem. Second, responses to questions 3, 4, 7, 8, and 11 indicate there is an important local

component to the area’s nonattainment problem. The responses to questions 4, 5 and 12 indicate

that high ozone concentrations may be observed under several sets of meteorological conditions.

The responses to questions 7, 8, and 11 suggest that ozone in and near the nonattainment area

may be responsive to both VOC and NOx controls and that the extent of this response may vary

spatially. The response to question 6 suggests that it may be appropriate to develop a strategy

using a model with 12 km grid cells.

The preceding conceptual description implies that the State/Tribe containing the

nonattainment area in this example will need to involve stakeholders from other, nearby

States/Tribes to develop and implement a modeling/analysis protocol. It also suggests that a

nested regional modeling analysis will be needed to address the problem. Further, it may be

necessary to model at least several distinctive types of episodes and additional analyses will be

needed to select episodes. Finally, sensitivity (i.e., diagnostic) tests, or other modeling probing

tools, will be needed to assess the effects of reducing VOC and NOx emissions separately and at

the same time.


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