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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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Presentation Transcript
slide1

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)
slide3

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 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
slide4

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

slide5

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 SO2 and SO4 near Big Bend attribute 75% of SO2 to “local” sources and 90% of SO4 to “regional” sources
slide8

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

slide11

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
slide12
Preliminary Particulate Sulfur Source Attributions for BRAVO by Trajectory Mass Balance Regressions- Kristi Gebhart, NPS
slide14

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
air quality modeling
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)
slide16

Big Brown tracer and Observed S

Big Brown tracer

August- Particulate S and observed iPPCH

Observed S

slide17

August- CMAQ and observed iPPCH

12km CMAQ and 36km REMSAD Big Brown tracer

obs/preds time series for sequestered period

Look at CMAQ first…

Obs

Preds

slide18

August- REMSAD and observed iPPCH

12km CMAQ and 36km REMSAD Big Brown tracer

obs/preds time series for sequestered period

Now REMSAD…

Obs

Preds

slide19

Houston tracer and observed S

Houston tracer

October- Particulate S and observed PTCH

Observed S

slide20

October- CMAQ and observed PTCH

12km CMAQ and 36km REMSAD Houston tracer

obs/preds time series for sequestered period

Look at CMAQ first…

Obs

Preds

slide21

12km CMAQ and 36km REMSAD Houston tracer

obs/preds time series for sequestered period

October- REMSAD and observed PTCH

Now REMSAD…

Obs

Preds

slide22

REMSAD PTCH

REMSAD vs. CMAQ

36 km vs. 12 km PTCH (Houston Tracer)

October 12

Graphics from AER

36 km

12 km

slide24

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
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