(BRAVO) Study: Final Report. - Desert Research Institute

Final Report — September 2004
Table 9-13. Definitions of performance statistics used in this report.
Mean or Average
Simulated or
Predicted
1
N
∑ P i
N i=
1
Observed
1
N
∑O i
N i=
1
Coefficient of Determination R 2
Mean Bias
Mean Error
N
1
∑(
P i
− O i
)
N 1
i=
N
1
∑ ( P i
− O i
)
N 1
Fractional Bias (%) Mean Normalized Bias (%)
2 ( P − Oi
)
N 1 O )
N
i
∑
i= ( Pi
+
i
i=
N
1 ( Pi
− Oi
)
∑
N 1 O
Fractional Error (%) Mean Normalized Error (%)
2
P − Oi
O
N
i
∑
N i= 1 Pi
+
i
1
i=
N
∑
N i=
1
i
P − O
i
O
i
i
Root Mean Square (RMS) Error
1 N
∑( P i
− O i
)
N
i=
1
2
Note, however, that the intersite correlations between the SO 2 measurements
themselves are also low, as shown in Table 9-14. For example, the coefficient of
determination between the K-Bar and San Vicente observed SO 2 time series is r 2 = 0.18, and
between K-Bar and Persimmon Gap it is only 0.01, even though these sites are within
relatively close proximity. (K-Bar is approximately 40 km south of Persimmon Gap and 30
km north of San Vicente.) Also, the average and peak SO 2 concentrations recorded during
the four-month field study were considerably higher at Persimmon Gap than at the other two
sites. This lack of correlation between the SO 2 time series at the different Big Bend
monitoring sites may be due to plumes from local sources (i.e., Carbón I/II) that are affected
by the complex terrain in the area of the park. For example, the San Vicente monitor lies in a
valley floor near the Rio Grande, and is 400 to 500 m lower than the K-Bar and Persimmon
Gap monitors; San Vicente may be impacted by plumes traveling up the river valley that do
not reach the higher-elevation sites. In any case, the low correlations between measured
concentrations in the same or contiguous 36-km cells needs to be taken into account when
evaluating model performance for SO 2 .
9-41