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

Final Report — September 2004
for source apportionment and thus is the only configuration whose performance will be
addressed here.
The four continuously-released perfluorocarbon tracers used for this evaluation were
released from Eagle Pass (oPDCH), San Antonio (PDCB), Houston (PTCH), and northeast
Texas (i-PPCH), as described in Section 3.2. From early July to mid September, PTCH and
PDCB “timing” tracers were released intermittently from Eagle Pass in addition to the
continuous tracer. As was shown in Figure 3-2, six monitoring stations – San Vicente, K-
Bar, Persimmon Gap, Marathon, Fort Stockton and Monahans Sandhills – measured tracer
concentrations near and north of Big Bend with 6-hour samples during the study.
The time series of the measured and simulated concentrations at K-Bar for the four
continuously-released tracers are shown in Figures 9-21 to 9-24. The concentrations in these
plots are in parts per quadrillion (ppq), which is equivalent to femtoliters per liter (fl/l).
For the northeast Texas tracer, “negative” or zero concentrations were observed
during much of the 4-month period, as shown in Figure 9-21. Indeed, the average
concentration was slightly negative at K-Bar, which suggests that the estimated background
concentration that was subtracted from the laboratory-measured concentration may have been
too large. Only a few measurements were observed where the tracer signal was clearly
distinguishable from the noise. The highest observed concentrations (~0.2 ppq) occurred in
the last part of October and several lower peaks (0.05 to 0.1 ppq) were observed in July,
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
-0.05
7/ 1 7/ 11 7/ 21 7/ 31 8/10 8/20 8/ 30 9/9 9/19 9/29 10/ 9 10/19 10/ 29
0.40
0.30
0.20
0.10
0.00
7/1 7/11 7/21 7/31 8/10 8/20 8/30 9/9 9/19 9/29 10/9 10/19 10/29
Figure 9-21. Measured (top) and CMAQ-simulated (bottom) time series of NE Texas tracer
concentrations (in ppq) at K-Bar.
9-46