Overview of the Big Bend Regional Aerosol and Visibility Observational (BRAVO) study:
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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

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  • 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)



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Tracer transport locations

  • 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 12-18 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


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


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Some findings scattering dominated extinction

  • 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 SO2 and SO4 near Big Bend attribute 75% of SO2 to “local” sources and 90% of SO4 to “regional” sources


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TAGIT-SO2 method results scattering dominated extinction


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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




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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


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


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Results using MM5 36-Km Winds by Trajectory Mass Balance Regressions- Kristi Gebhart, NPS


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Preliminary Source Attributions from Trajectory Mass Balance Regressions

  • Carbon I/II – 0 - 18%

  • East Texas – 36 - 42%

  • Monterrey Region, Mexico City & Volcano – 20 - 30%

  • El Paso Region – 0 - 7%

  • Eastern U.S. – 0 - 7%

  • Western U.S. – negligible


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Air Quality modeling Regressions

  • 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)


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Big Brown tracer and Observed S Regressions

Big Brown tracer

August- Particulate S and observed iPPCH

Observed S


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August- CMAQ and observed iPPCH Regressions

12km CMAQ and 36km REMSAD Big Brown tracer

obs/preds time series for sequestered period

Look at CMAQ first…

Obs

Preds


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August- REMSAD and observed iPPCH Regressions

12km CMAQ and 36km REMSAD Big Brown tracer

obs/preds time series for sequestered period

Now REMSAD…

Obs

Preds


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Houston tracer and observed S Regressions

Houston tracer

October- Particulate S and observed PTCH

Observed S


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October- CMAQ and observed PTCH Regressions

12km CMAQ and 36km REMSAD Houston tracer

obs/preds time series for sequestered period

Look at CMAQ first…

Obs

Preds


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12km CMAQ and 36km REMSAD Houston tracer Regressions

obs/preds time series for sequestered period

October- REMSAD and observed PTCH

Now REMSAD…

Obs

Preds


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REMSAD PTCH Regressions

REMSAD vs. CMAQ

36 km vs. 12 km PTCH (Houston Tracer)

October 12

Graphics from AER

36 km

12 km



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Modeling status Regressions

  • 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


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