(BRAVO) Study: Final Report. - Desert Research Institute
(BRAVO) Study: Final Report. - Desert Research Institute
(BRAVO) Study: Final Report. - Desert Research Institute
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<strong>Final</strong> <strong>Report</strong> — September 2004<br />
2.0<br />
Eagle Pass tracer<br />
mixing ratio (ppqV)<br />
1.5<br />
1.0<br />
0.5<br />
0.0<br />
7/1<br />
7/8<br />
7/15<br />
7/22<br />
7/29<br />
8/5<br />
8/12<br />
8/19<br />
8/26<br />
9/2<br />
9/9<br />
9/16<br />
9/23<br />
9/30<br />
10/7<br />
10/14<br />
10/21<br />
10/28<br />
-0.5<br />
date 1999<br />
Figure 9-14. Comparison of 24-hr three-site average REMSAD predictions (red) of the<br />
spatially-averaged concentrations in Big Bend National Park versus three-site average<br />
measurements (blue) for the continuous Eagle Pass tracer.<br />
At Big Bend National Park, the spatially-averaged measured concentration of the<br />
tracer released from Eagle Pass (Figure 9-14) generally ranges between 0 and 1 ppq during<br />
the four month study period, with a peak of 1.6 ppq observed on 25 September. Tracer “hits”<br />
are generally well replicated by REMSAD, although the average predicted value of 0.39 ppq<br />
is nearly twice the observed value of 0.22 ppq, and from mid-August through September<br />
there is a clear tendency for REMSAD to overstate tracer concentrations. Also, the modeled<br />
concentrations do not vary as much as the measured ones.<br />
In contrast to the Eagle Pass tracer, the model underestimated the mean<br />
concentrations of the Houston and San Antonio tracers (Figures 9-16 and 9-17). For the<br />
northeast Texas tracer, the measurements of which were barely above the analytical noise<br />
and for which the background-adjusted concentrations were often negative, the correlation<br />
coefficient was a surprising 0.34 (r 2 = 0.12), but the model significantly overstated the<br />
measured concentrations.<br />
In general, it appears that the performance of the model was best for the tracers<br />
released closest to the park (at Eagle Pass and San Antonio), and became poorer as the<br />
transport distance increased (as to Houston and northeast Texas). The distance also affected<br />
the concentrations of the actual tracers at the park, so the more distant tracer concentrations<br />
were the least reliable. Interestingly, the poorer performance corresponded with the tracers<br />
released into power plant stacks (at Houston and northeast Texas) instead of near ground<br />
level (at Eagle Pass and San Antonio). Whether the resulting more-elevated transport played<br />
a role in the performance comparison is an open question.<br />
9-36
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