frequency of favorable meteorological combinations provides a means for considering
meteorological differences as a mitigating factor in observed ozone trends.
More recently, Milanchus, et al. (1998) and Hogrefe, et al. (2000) have described a
procedure which is able to suppress short term variability in observed ozone attributable to
diurnal and synoptic differences (i.e., general differences over a wide area or seasonal
variations) so that underlying base level trends can be discerned.
Perhaps the simplest procedure for normalizing an observed trend for meteorological
differences is to fit a curve through observed values of a trend parameter over the 10 years
preceding the mid-course review. In the following discussion, this is illustrated for the
maximum observed ozone design 9across all monitors in the area) value in each year. The
fitted curve is used in concert with observed maximum design values in each year to calculate
residual values for each year (i.e., the difference between the design value indicated by the
fitted curve and the actual observation). These residuals may be used to account for
variability in meteorology as described in the following paragraphs.
To illustrate, Table 2.2 shows hypothetical data for a 10-year period.
Table 2.2. Example Of Best Fit Design Values And Residuals
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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