# Presentation: 448471

## 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 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

## 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

## Slide 6

## 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  –  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)

## 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

- Look at CMAQ first...

- Obs

- Preds

## 12km CMAQ and 36km REMSAD Big Brown tracer 

- obs/preds time series for sequestered period

- 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

- Look at CMAQ first...

- Obs

- Preds

## 12km CMAQ and 36km REMSAD Houston tracer 

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

- Now REMSAD...

- Obs

- Preds

## REMSAD vs. CMAQ

**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 

***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