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

Final Report — September 2004
Overestimates and underestimates were relatively evenly distributed over the other weeks,
which resulted in the small average bias given in the last column of Table 9-20.
Turning now to the Big Thicket Station in the eastern part of the domain,
performance statistics were given in Table 9-21. For all species and time scales of
comparison, the mean normalized bias corresponds to a large portion of the normalized error,
indicating the model rarely underestimated the measured concentrations. On average, the
model’s SO 2 concentration estimates are 3.4 times as great as the observations.
Daily SO 2 estimates are plotted alongside concentrations measured at Big Thicket in
Figure 9-27. The model overestimates on 64 of the 75 days with valid observations and the
coefficient of determination is low (r 2 = 0.28). However, as shown in Table 9-21, model
performance improves substantially when weekly SO 2 concentrations were compared, with
the r-squared value increasing to 0.65, although weekly SO 2 concentrations were estimated in
almost all weeks.
16
SO2 (µg/m 3 )
12
8
4
0
7/2 7/16 7/30 8/13 8/27 9/10 9/24 10/8 10/22
24
20
SO 4
2– (µg/m
3 )
16
12
8
4
0
7/2 7/16 7/30 8/13 8/27 9/10 9/24 10/8 10/22
Figure 9-27. Measured and simulated daily SO 2 concentrations (top) and fine sulfate
concentrations (bottom) at Big Thicket. The points represent the observations and the line
represents the simulated concentrations.
9-59