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

Final Report — September 2004
Performance statistics for the same data at all three locations individually are given in
Table 9-12. Definitions of those statistics, which are used in this report for describing both
REMSAD and CMAQ performance, are given in Table 9-13. In Table 9-12, note that the
San Vicente and K-Bar sites, which are approximately 30 km apart, fall within the same
REMSAD 36 km grid cell, and hence the modeled concentrations for these two sites will be
the same, even though the measured concentrations at the two locations may differ. The
averages in Table 9-12 show small differences, though, because differing numbers of valid
measurement samples dictate different numbers of both measured and corresponding
modeled daily values for each location and for each variable. Also, the observed total sulfur
calculation requires concentrations of both SO 2 and sulfate, and thus encompasses fewer days
than either of these components.
Table 9-12. Performance statistics over the full BRAVO Study period for REMSAD simulations of
SO 2 , sulfate, and total sulfur at the three sampling locations within Big Bend National Park.
K-Bar San Vicente Persimmon Gap
SO2 SO4 = TS SO2 SO4 = TS SO2 SO4 = TS
Avg. Observed (ug/m 3 ) 0.69 2.47 1.19 0.60 2.59 1.19 1.43 2.71 1.63
Avg. Simulated (paired) (ug/m 3 ) 1.84 2.02 1.69 1.75 2.05 1.66 2.00 2.30 1.80
r 2 0.09 0.25 0.31 0.12 0.27 0.34 0.15 0.25 0.29
Regression Slope 0.47 0.48 0.61 0.51 0.50 0.66 0.31 0.51 0.50
Intercept (ug/m 3 ) 1.52 0.83 0.96 1.45 0.75 0.88 1.56 0.91 0.99
Mean Normalized Error (%) 357 62 106 413 59 103 200 56 62
Mean Normalized Bias (%) 352 1 91 404 -5 86 186 1 40
Fractional Error (%) 99 60 57 112 59 57 71 52 42
Fractional Bias (%) 92 -28 38 102 -32 35 53 -24 16
Table 9-12 shows a tendency for REMSAD to overstate SO 2 concentrations at K-Bar
and San Vicente, with very large mean normalized biases of 352 and 404%, respectively (i.e.,
on average, REMSAD overestimates the measured SO 2 concentrations at these two locations
by roughly a factor of five). The average bias is less, but still large, at Persimmon Gap,
where the mean normalized bias is 186%. The coefficient of determination (r 2 ) between
measured and modeled SO 2 concentrations is uniformly low at these sites, ranging between
0.09 and 0.15.
9-40