Tracer Simulation and Analysis of Transport Conditions Leading to Tracer Impacts at Big Bend Bret A. Schichtel ( NPS/CIRA Fort Collins, CO BRAVO Study Data Analysis Meeting San Antonio, TX March 23, 2001

Tracer Monitoring Network Table 3: Phase 2 tracer release rates and schedule. Location Unit Tracer Release Rate (g min -1 ) Release Schedule Eagle Pass 1 oPDCH 2.6 continuous 7/5/99- 11/1/99 San Antonio 5 PDCB 7.4 continuous 9/17/99– 11/1/99 Houston 6 PTCH 1.9 Continuous 9/17/99– 11/1/99 Big Brown 4 iPPCH 1.5 Continuous 7/9/99– 11/1/99 From Watson et. Al., 2000 Sequestered Data: 8/5-10/1 10/9 – 10/16 The tracer data was supplied by Mark Green and is preliminary This analysis looks only at Eagle Pass and Big Brown tracer simulations since data in both July and October were available.

Eagle Pass & Big Brown Tracer at Big Bend (K-Bar) (24 hour Moving Average) The largest Big Brown and Eagle Pass tracer hits often coincide. Exception: Eagle Pass hit precedes Big Brown on 7/31-8/4 episode. Eagle Pass Big Brown

CAPITA Monte Carlo Model - Transport Advection: Particles are moved in 3-D space using the input meteorological data’s mean wind field. Horizontal Dispersion: Eddy diffusion coefficients, which vary depending on time of day, randomly displace the particles horizontally. Vertical Dispersion: Intense vertical mixing within the mixing layer is simulated by uniformly distributing particle from the ground to the mixing height. No vertical dispersion is applied to particles above mixing layer.

HY-SPLIT: NGM wind fields, no mixing Monte Carlo Model:NGM wind fields, mixing At times individual Airmass histories compared very well At times individual Airmass histories compared very poorly Airmass History Model Comparison HY-SPLIT Vs. CAPITA Monte Carlo Model

EDAS Meteorological Data Archive The EDAS (Eta Data Assimilation System) data are a product of the NWS' National Centers for Environmental Prediction (NCEP). EDAS is a data assimilation system consisting of successive 3-h Eta model forecasts and Optimum Interpolation (OI) analyses. 79 by 55 Lambert Conformal grid ~ 80 km resolution. 22 vertical layers on constant pressure surfaces from 1000 to 50 mbar 3 hour time increment Upper Air Data: 3-D winds, Temp, RH Surface Data includes: pressure, 10 meter winds, 2 meter Temp & RH, Momentum and heat flux Data is available from 1/97 to present. Note Oct data is unavailable due to a fire at NCEP

FNL Meteorological Data Archive The FNL data is a product of the Global Data Assimilation System (GDAS), which uses the Global spectral Medium Range Forecast model (MRF) to assimilate multiple sources of measured data and forecast meteorology. 129 x 129 Polar Stereographic Grid with ~ 190 km resolution. 12 vertical layers on constant pressure surfaces from 1000 to 50 mbar 6 hour time increment Upper Air Data: 3-D winds, Temp, RH Surface Data includes: pressure, 10 meter winds, 2 meter Temp & RH, Momentum and heat flux Data is available from 1/97 to present.

Monte Carlo Tracer Simulation The tracer was simulated by releasing 100 particles an hour from each release site and tracking their movement for 5 days. EDAS winds: July 1 – Sept. 31 FNL winds: Oct Tracer Release Heights Eagle Pass:100 m Big Brown:400 m Houston:400 m San Antonio:20 m Click on picture to animate

Eagle Pass Tracer Simulation Simulated tracer coincides with Eagle Pass tracer episodes Delay between measured and simulated tracer hits – Particularly during the 7/31-8/4 episode.

Big Brown Tracer Simulation Simulations generally predict less tracer than was measured. Note a complete miss of the July tracer hit.

Simulated Tracer Episode 7/8-7/13 Flow reversal causes accumulation of particles and mixing of plumes prior to impact Delay in plume hits and loss of particles at end of episode (5 days may not be enough)

Simulated Tracer Episode - 7/19-7/24 Both Eagle Pass and Big Brown tracer were measured at Big Bend. During this episode, the transport is persistently to the north northwest. Could the tracer data be wrong?

Simulated Tracer 7/31-8/4 Episode Eagle Pass tracer impacts Big Bend but simulation is to the East. Transport shifts from south-southwesterly to north-northeast flow mixing the plumes. The simulated mixed plumes never impact Big Bend

Simulated Tracer Episode 10/3 -10/7 Re-circulation over E. Texas allowed for particle (tracer) accumulation prior to impacting K-Bar

Simulated Tracer 10/21-10/27 Episode

Conclusions Big Brown and Eagle Pass tracer often hit K-Bar during the same “episodes” Prior to large tracer hits periods of airmass stagnation, flow reversals, and/or re-circulation were seen mixing the plumes from the eastern Texas sources. Monte Carlo and HYSPLIT models and EDAS/FNL winds capture the tracer episodes. However: There are temporal displacements in impacts with Eagle Pass simulated tracer often to the east of Big Bend. The models clearly miss the July episodes. Simulated tracer does not hang around long enough The poor simulation are not unexpected due to: complex transport (flow reversals, etc.) dominates prior to impact. Mesoscale flows may be important due to the complex terrain and proximity of Eagle Pass

Disclaimers These are preliminary results based upon coarse meteorological data. The analysis will be repeated once the high resolution BRAVO meteorological data are available. In addition, these results will be compared against BRAVO modeling and other air quality data analyses as they become available. Support for this BRAVO Study-related work was provided by the National Park Service. However, the results, findings, and conclusions expressed in this paper are solely those of the authors and are not necessarily endorsed by the management, sponsors, or collaborators of the BRAVO Study. A comprehensive final report for the BRAVO Study is anticipated in early 2002.