Overview of the Big Bend Regional Aerosol and Visibility Observational (BRAVO) study:  Understand the long-range, trans-boundary transport of visibility-reducing particles from regional sources in the U.S. and Mexico  Quantify contributions of U.S. and Mexican source regions responsible for poor visibility at Big Bend NP BRAVO conducted during July-October 1999  Large network of aerosol and SO2 monitoring sites, tracer released from 4 locations, additional upper air measurements  Specialized aerosol measurements at Big Bend  Extensive data analysis and modeling (MM5,REMSAD, CMAQ)

BRAVO aerosol and tracer monitoring sites and tracer release locations

Tracer transport Eagle Pass tracer > detection limit at the 6 hour sites 16% to 59% of the time (most frequently at northern sites) Timing tracers from Eagle Pass indicated transport times most often hours Northeast Texas and Houston area tracers hit 6 hour sites infrequently and tends to hit all sites during an episode (broader plume) San Antonio tracer > detection limits 15% to 34% of the time with several periods of short-term impacts at most or all sites

4 major episodes, 2-4 days duration Sulfate scattering dominated extinction

Some findings Sulfates dominated fine mass budget, followed by carbon, crustal Secondary organics identified as important by organic speciation, but could not be apportioned Some periods of African dust (July, August) identified from calcium deficiency, backtrajectories Spatial pattern analysis (TAGIT) of SO 2 and SO 4 near Big Bend attribute 75% of SO 2 to “local” sources and 90% of SO 4 to “regional” sources

TAGIT-SO2 method results

HYSPLIT Residence time for entire BRAVO study- flow mostly from SE along border area Residence time worst 20% light scattering (6-hour periods) flow more from NE prior to along border area

This episode appeared to have transport from eastern US

Weak cold front passes through area, bring flow from the NE behind front-episode 3

Conceptual model for late summer/early fall haze episodes at Big Bend Weak early season cold front approaches Texas SE flow ahead of front brings emissions from sources in east Texas/Gulf Coast inland under humid conditions Northeast-east flow after frontal passage carries polluted airmass toward Big Bend Flow returns to typical SE as it approached Big Bend, also carrying emissions from border area Absolute worst-case had “back-door cold front approach from NE, carrying sulfur compounds from eastern US in additional to regional and local emissions

Preliminary Particulate Sulfur Source Attributions for BRAVO by Trajectory Mass Balance Regressions- Kristi Gebhart, NPS

Results using MM5 36-Km Winds

Preliminary Source Attributions from Trajectory Mass Balance Regressions Carbon I/II – % East Texas – % Monterrey Region, Mexico City & Volcano – % El Paso Region – 0 - 7% Eastern U.S. – 0 - 7% Western U.S. – negligible

Air Quality modeling MM5 with 36 and 12 km grids entire 4 months, 4 km near Big Bend two 10-day episodes CMAQ for two 10-day episodes REMSAD for entire 4 months (36 km and 12 km)

August- Particulate S and observed iPPCH Big Brown tracer and Observed S Big Brown tracer Observed S

12km CMAQ and 36km REMSAD Big Brown tracer obs/preds time series for sequestered period August- CMAQ and observed iPPCH Look at CMAQ first…Obs Preds

12km CMAQ and 36km REMSAD Big Brown tracer obs/preds time series for sequestered period August- REMSAD and observed iPPCH Now REMSAD…Obs Preds

October- Particulate S and observed PTCH Houston tracer and observed S Houston tracer Observed S

12km CMAQ and 36km REMSAD Houston tracer obs/preds time series for sequestered period October- CMAQ and observed PTCH Look at CMAQ first… Obs Preds

October- REMSAD and observed PTCH 12km CMAQ and 36km REMSAD Houston tracer obs/preds time series for sequestered period Now REMSAD… Obs Preds

REMSAD PTCH 36 km 12 km REMSAD vs. CMAQ 36 km vs. 12 km PTCH (Houston Tracer) October 12 Graphics from AER

SO4 at K-BAR, August-October 1999 from CIRA

Modeling status Modeling work is on-going Additional work being done (CMAQ at 36 km, etc.) to help understand CMAQ transport problems REMSAD and CMAQ sensitivity tests to assess contributions to sulfate from Mexico, east Texas, west Texas, non-Texas US areas