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 MexicoQuantify contributions of U.S. and Mexican source regions responsible for poor visibility at Big Bend NP BRAVO conducted during July-October 1999Large network of aerosol and SO2 monitoring sites, tracer released from 4 locations, additional upper air measurements Specialized aerosol measurements at Big BendExtensive 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 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

bsp and estimated SO4 scattering

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24 hr SO4 scat 24 hr bsp

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

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Table 6. Use of SO2 for attribution of particulate sulfur BIBE FTST MARA MONA PRSG SNVI ALL Average attribution (ng/m3)

13618 3821 9521 21522 13820 4221 919

% of particulate sulfur

14.41.9 4.32.4 10.12.2 20.22.0 14.02.0 4.62.4 9.81.0

. Table 7. Use of SO2 for attribution of SO2 BIBE FTST MARA MONA PRSG SNVI ALL Average attribution (ng/m3)

54676 103780 86778 4483524 1062105 35857 79538

% of SO2 6810 766 767 9411 798 6110 754 Table 8. Use of SO2 for attribution of total sulfur BIBE FTST MARA MONA PRSG SNVI ALL Average attribution (ng/m3)

40850 55651 52952 2456273 66965 22141 48824

% of total sulfur 314 363 353 718 404 193 332

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

Episode 2 Influence functions

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 EDAS/FNL wind fields with start heights of 10, 100, 200, 500, and 1000m

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Mean Obs = 831.507Mean Pred = 814.318

Max Traj Height (m) = 10000

24-hr PS, CAPITAMCCOMBO.10PART, Source Set 3

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Mean Obs = 815.471Mean Pred = 805.848

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24-hr PS, COMBO, Source Set 3

Results using MM5 36-Km Winds

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Mean Obs = 838.349Mean Pred = 848.192

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Mean Obs = 815.471Mean Pred = 810.246

Max Traj Height (m) = 10000

24-hr PS, MM5WTC, Source Set 3

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

• 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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August- Particulate S and observed iPPCH

Big Brown tracer and Observed S

Big Brown tracer

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12km CMAQ and 36km REMSAD Big Brown tracer obs/preds time series for sequestered period

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August- CMAQ and observed iPPCH

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12km CMAQ and 36km REMSAD Big Brown tracer obs/preds time series for sequestered period

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August- REMSAD and observed iPPCH

Now REMSAD… Obs

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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

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Look at CMAQ first…

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October- REMSAD and observed PTCH

12km CMAQ and 36km REMSAD Houston tracer obs/preds time series for sequestered period

Now REMSAD…

Obs

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REMSAD PTCH

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REMSAD vs. CMAQ36 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