An Overview of the Big Bend Regional Aerosol and Visibility Observational

(BRAVO) Study

Marc Pitchford, Ph.D

National Oceanic and Atmospheric Administration

Mark Green, Ph.D.

Desert Research Institute

Reasons for the Study

• Clean Air Act provides protection from visibility impacts at certain national parks and wilderness areas including Big Bend

• Popular perception in the region that haze levels have been increasing at Big Bend

• Concerns that increased emissions along the US/Mexico border are responsible for haze increases

• Preliminary Big Bend Haze Study called for a source attribution study

Photos

BRAVO Study Participants

U.S. Activities

EPA Sponsor, project management & direction

NPS Sponsor, project management & modeling

TNRCC Sponsor, project coordination, aircraft monitoring, data analysis

EPRI Sponsor, met. and air quality modeling

NOAA Technical management, tracer release, upper air met. & data analysis

DRI Technical management, database, data analysis, emissions inventory, and emissions characterization

BNL Tracer sample analysis

UCD Aerosol monitoring and analysis, tracer sampling

CIRA Aerosol monitoring size and composition special studies at Big Bend

ARS Continuous optical & met. monitoring, photos, special study support

ENSR Independent quality assurance auditors

Mexico Activities

PROFEPA Project management & direction [involvement discontinued during planning phase]

Seasonality and components of haze

Aerosol light extinction:

Sulfate 41%

Organic Carbon19%

Black Carbon 21%

Crustal 16%

Nitrate 4%6

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10%ile 50%ile 90%ile

Transport patterns – late July, late September

SO2 emissions

Distance weighted SO2 emissions

Frequency weighted SO2 emissions

Seasonality of transport to Big Bend

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Summary of Field Study

• 4 month study from July-October• Tracer release near Carbon I/II (Eagle Pass- 3

tracers) and Big Brown first half• Tracer release from Eagle Pass, San Antonio,

W.A. Parish, Big Brown 2nd half• Large particulate and tracer monitoring

network (but none in Mexico)• Additional upper air measurements• Visibility measurements at Big Bend• “Special” studies at Big Bend• Aircraft measurements

BRAVO particulate, SO2, and tracer monitoring network

Tracer Release Equipment

Big Bend Specialized Measurements

Measurements Averaging Period

High time resolution, high sensitivity SO2 1-hour

High time resolution particulate sulfate 12-minutes

High time resolution perfluorocarbon tracer 1-hour

PM2.5 carbonaceous aerosol 24-hour

Carbon speciation (GC/MS) for selected periods 24-hour

Gaseous nitric acid 24-hour

Gaseous ammonia 24-hour

Gaseous hydroperoxides 1-hour

MOUDI size-resolved aerosol ions 24-hour

DRUM size-resolved aerosol elements 1-hour

Various particle size monitors – DMA, OPC, etc. Minutes

Various optical measurements – nephelometers, transmissometers, aetholometers, etc

Minutes

Scanning electron microscopy - selected samples 24-hour

Data Recovery

• Particulate sampling network– Complete deployment delayed ~3 weeks for new

samplers– Otherwise expect high recovery

• Tracer sampling network– Extended period in middle of study with only 6 tracer

sampling sites due to delayed analysis capability– Most extensive tracer study ever done, even

considering periods with only a few sites

• High data recovery for other monitoring (visibility, meteorology, air quality)

Status of Data from Field Study

Tracer release dataSurface and upper air (Radar wind profiler) Light scattering (haze)12-minute Sulfate, hourly SO2 at Big Bend

Photographs at Big BendLimited Big Bend aerosol chemical analysis

Status of Data from Field Study

• Light extinction data – December, 2000

• Complete chemical analysis of particulate data – November, 2000

• Tracer data – January, 2001

• Source profiles – November, 2000

• Emissions – February, 2001

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Hourly Extinction Coefficient

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Data Analysis Process

• Descriptive analysis – maps and time plots of variables, mean, standard deviation, etc.

• Association analysis – relationships among variable, e.g. correlations, closure

• Representativeness of study period• Attribution analysis- source and receptor

models, etc.• Reconciliation of results• Conceptual model

Attribution Analysis

• Multiple air quality simulation & receptor modeling methods used for attribution

• Tracer data divided into subset for “training” and a sequestered subset for “testing” to evaluate methods’ performance

• Study findings are developed by reconciling results of the various methods

BRAVO MM5 Met. Modeling Domains

36 km

12 km

4 km

Cell Sizes

BRAVO Emissions Inventory Data SourcesU.S. Mexico Off Shore

Point NET & CEM (large sources)

INE for 20 major cities

MMS-MOAD3

Area NET except Texas

TNRCC in Texas

INE for 20 major cities; scaled by population elsewhere

N/A

Mobile NET except Texas

TNRCC in Texas

INE mobile emissions scaled by population

TNRCC & MMS-MOAD3

Biogenic BEIS-2 with land-use data

BEIS-2 with land-use data

N/A

Fire AVHRR, GOES, & TOMS satellite imagery

AVHRR, GOES, & TOMS satellite imagery

N/A

Estimated Schedule

• Always takes longer than planned

• Get all data into database – autumn 2000

• Data analysis and modeling – end of 2001

• Reconciliation of results – March 2002

• Draft Report – May 2002

• Final report July 2002