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

Final Report — September 2004
9.11.2 Base Case Performance
Focusing now solely on the new base case configuration, Table 9-18 shows statistics
illustrating the performance of the CMAQ-MADRID base case simulation in simulating
24-hr fine particulate matter component concentrations at the K-Bar site.
As indicated by the coefficient of determination (r 2 ), the model accounts for 52% of
the variance in fine sulfate mass and only 23% of the variance in total fine particulate mass at
Big Bend. The mean normalized error in the predictions for all species is greater than 50%;
however, the mean normalized error is species-dependent and ranges from 51% and 55% for
ammonium and sulfate to 96% for nitrate at the K-Bar site.
Model performance over multiple monitoring locations in the BRAVO Study network
is summarized in Table 9-19. Note that the number of monitoring locations differed for
different components. (Ammonium and nitrate concentrations were measured only at Big
Bend and thus are not included in this table.)
Thirty-seven stations measured fine sulfate and total fine particulate matter (PM 2.5 ).
Consistent with the behavior at Big Bend, Table 9-19 shows that the model exhibited positive
bias (both absolute and relative) in its predictions of fine particulate sulfate, together with
negative absolute bias and positive normalized (relative) bias in its predictions of total fine
particulate mass.
Table 9-18. CMAQ-MADRID performance for 24-hr averages of particulate matter components at
K-Bar over the duration of the BRAVO study. 2
Statistic units SO4 2– NO3 – NH4 + EC OM PM2.5
Observed mean µg/m 3 2.49 0.23 0.82 0.23 1.25 6.33
Simulated mean µg/m 3 2.61 0.03 0.7 0.05 0.45 4.61
Coeff. of determination (r 2 ) 0.52 0.01 0.47 0.13 0.1 0.23
Mean bias µg/m 3 0.12 -0.19 -0.12 -0.18 -0.8 -1.72
Mean error µg/m 3 1.08 0.21 0.35 0.18 0.81 3.09
Mean Normalized Bias % 20 -79 7 -76 -59 7
Mean Normalized Error % 55 96 51 76 62 70
Fractional Bias % 0 -166 -12 -135 -98 -31
Fractional Error % 46 173 48 135 100 62
RMS error µg/m 3 1.51 0.24 0.45 0.14 1.08 4.05
2 A threshold of 0.1 µg/m 3 was used for all species in such statistical tables throughout this section,
except for Table 9-22.
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