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

Final Report — September 2004
The same analysis (not shown here) was also carried out for the daytime tracer PTCH
and its results are consistent with the ones shown here.
A method of directly estimating transport times was to assign each ambient sample to
one of four 12-hour release periods in each 48-hour period whenever the continuous tracer
was significantly above background (more than twice the uncertainty above background).
This was done by using both the alternate day and daytime tracers, in which case each
12-hour period has a unique combination of tracers being released, and assuming a transport
time of less than 48 hours. Using this method, the percentages of estimated transport times
for each 6-hour range, averaged over all sites, are shown in Figure 5-26. The peak of the
estimated transport time distribution is at 15 hours, which corresponds to transport speeds of
about 5-6 m/s, depending upon the distance to the monitoring site.
All sites
30
% in 6-hour period
25
20
15
10
5
0
day
night
0 6 12 18 24 30 36 42 48
Transport time (hours)
Figure 5-26. Distribution of estimated
transport times of Eagle Pass tracers to
6-hour monitoring sites in each 6-hour
period during the timing tracer study (7/5/99-
9/13/99). Percentages are averaged over all
6-hour sampling sites separately for daytime
and nighttime releases.
5-33