The following is a procedure that may be used to assist in

selecting modeling episodes. Other techniques may be considered on

a case-by-case basis; they should be described in the Modeling

Protocol and approved by the appropriate EPA Regional Office.

Identification of meteorological regimes for a given area

under review begins with constructing a climatological windrose of

high ozone days. The windrose is constructed by first selecting

all days from the period 1987 to present during which at least one

ozone monitor within the area recorded an exceedance of the ozone

NAAQS or some other cutoff level (e.g., 100 ppb). Additional years

of data are encouraged in constructing the climatological windrose

(e.g., 1980-1991). Next, for each exceedance day, calculate the

morning (i.e., 7:00 a.m. - 10:00 a.m.) resultant wind velocity.

Then group the resultant wind velocities for all of the exceedance

days into eight compass directions plus calm, to establish a

climatic windrose of high-ozone days for the area under review.

Calm winds are defined as those with speeds less than 1.5 m/s and

referred to as the null wind direction. The windrose will include

nine bins (0-8); place the wind directions corresponding to the

eight compass points into bins 1-8, and the calm or null wind

direction into bin 0. The bins with frequencies significantly

higher than the average frequency for all bins should be defined as

the "predominant wind directions" (PWD).

Next, compare the morning (i.e., 7:00 a.m. - 10:00 a.m.)

resultant wind velocity for each exceedance day during 1987-89 and

more recent years with the climatic windrose of high-ozone days.

Categorize exceedance days with wind directions corresponding to

previously identified climatic PWD's as belonging to that PWD.

Lump all other exceedance days occurring during 1987-89 and later

into a category called "other." Rank each exceedance day within

each PWD category and within the "other" category according to its

areawide daily maximum ozone observation. Within each category,

the day with the highest areawide daily maximum concentration is

ranked first.

After the steps described in the two preceding paragraphs are

completed, meteorological regimes can be defined for use in the

attainment demonstration test described in Section 6.4. This may

be done as follows:



n1201 - n1202 - n1203 - n1204 - n1205 - n1206 - n1207 - n1208 - n1209 - n1210 - n1211 - n1212 - n1213 - n1214 - n1215 - n1216 - n1217 - n1218 - n1219 - n1220 - n1221 - n1222 - n1223 - n1224 - n1225 - n1226 - n1227 - n1228 - n1229 - n1230 - n1231 - n1232 - n1233 - n1234 - n1235 - n1236 - n1237 - n1238 - n1239 - n1240 - n1241 - n1242 - n1243 - n1244 - n1245 - n1246 - n12247 - n1248 - n1249 - n1250


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