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Chattanooga Modeling Study. Rick Gillam EPA Region 4 Air Modeler’s Workshop March 8-10, 2005. Presentation Topics. Summary of the Modeling Project Discussion of Results and Conclusions CALPUFF Issues / Lessons Learned. Chattanooga Then and Now. Chattanooga Modeling Study.

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Chattanooga Modeling Study

Rick Gillam

EPA Region 4

Air Modeler’s Workshop

March 8-10, 2005

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Presentation Topics

  • Summary of the Modeling Project

  • Discussion of Results and Conclusions

  • CALPUFF Issues/ Lessons Learned

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ChattanoogaThen and Now

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Chattanooga Modeling Study

  • EPA Region 4 received a request for modeling assistance from the Chattanooga Air Toxics Study (CATS) Stakeholder Advisory group (SAG) in April 2003

  • The purpose of this modeling was to help identify potential sources of the measured air concentrations of the following metals:

    • arsenic, chromium, manganese and nickel

  • Are large emission sources located outside the local Chattanooga area significantly contributing to measured air concentrations of these metals?

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Preliminary HYSPLIT Trajectory Analysis

  • Could a large coal-burning power plant, like Southern Company’s Plant Bowen, located approximately 100 kilometers from Chattanooga, have a significant contribution to measured air concentrations?

  • Prepared HYSPLIT backward and forward trajectories for periods of elevated concentrations to see if plumes from Plant Bowen could have impacted Chattanooga

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Refined Modeling Analysis

  • HYSPLIT trajectory analysis indicated that it was possible for Plant Bowen emissions to impact Chattanooga.

  • Decision made to use the CALPUFF model for a refined modeling analysis

  • Primary reason was CALPUFF is EPA’s recommended model for addressing long-range transport (up to 300 km) from point source emissions

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Modeling Domain and Emissions Inventory

  • Major Point Sources emitting the metals of concern within 100 km of Chattanooga were modeled

  • The modeling domain includes sources located in AL, GA, NC, and TN

  • A total of 226 sources were modeled

    • 42 sources in AL, 83 sources in GA

    • 2 sources in NC, and 99 sources in TN

  • EPA’s 1999 National Emissions Inventory (NEI) for Hazardous Air Pollutants (HAPs) was used to identify the sources

  • NEI contains all information needed to conduct the modeling (e.g, stack parameters, locations, emissions)

  • NEI consists of data from State/Local agencies, supplemented by TRI data and data from the emissions databases compiled for MACT rulemaking

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42 AL Sources

83 GA Sources

2 NC Sources

99 TN Sources

226 Total

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Modeling Receptors

  • The primary locations of interest for the modeling were the monitoring stations - receptors were placed at each of these locations

  • Also a small 20 km x 20 km grid with a coarse grid spacing was laid over the area surrounding the monitors to evaluate the potential for other elevated impacts

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Meteorological Data

  • The ambient air monitoring events occurred from November 1998 - October 1999

  • Meteorological data that covers this period was obtained from NOAA’s National Climatic Data Center (NCDC)

    • Surface data was purchased on CD’s in ISHD format (note ISHD data had to be converted to a format CALPUFF would accept)

    • Upper-air data was downloaded from the Radiosonde Data Access website (

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Modeling “Episodes”

  • To reduce the computer run time, discrete modeling “episodes “ were selected

  • Based on preliminary trajectory analyses using NOAA’s HYSPLIT model, the length of the episodes was chosen to be 72 hours

  • Of the 31 total 24-hr sampling events, 10 modeling episodes were selected

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CALMET Meteorological Model

  • A single meteorological station is not adequate for modeling long range transport

  • The CALPUFF modeling system includes the CALMET model

  • CALMET can use data from multiple surface and upper-air stations to develop hourly wind and temperature fields in a 3-dimensional modeling domain or it can use gridded meteorological model output (e.g., MM5 output)

    • also includes surface characteristics, terrain, and mixing heights

  • A 280 km x 250 km meteorological modeling domain, with 2 km grid spacing and 10 vertical layers was selected for this study

  • 11 surface stations and 4 upper-air stations were used to develop the met fields

  • CALMET was run for each of the 10, 72-hr modeling episodes identified previously

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CALPUFF Modeling

  • In the first phase, CALPUFF was run for each of the 10 modeling episodes, with separate runs for the sources located in each of the 4 states (10 episodes x 4 states = 40 runs)

  • Limited additional runs for Episode 3 (11/25/98) and Episode 18 (5/24/99) were also conducted

    • Runs using only sources located in Hamilton County, Tennessee

    • Runs using two individual sources located in Chattanooga, Eureka Foundry and Wheland Foundry

    • Runs using only Southern Company’s Plant Bowen located in Floyd County, Georgia

      • These runs were done to evaluate the potential for a large source located a long distance away to have impacts on the area.

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Modeling Output/CALPOST

  • CALPUFF produces an unformatted output file that contains the concentration estimates

  • To view the results, a post-processor CALPOST is used to extract the concentrations of interest

  • 192 CALPOST runs were done to extract 24-hr average concentrations corresponding to the time periods when sampling was conducted so direct comparisons could be made

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Example CALPUFF Results 18, 25Chromium for Episode 3

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Additional Efforts to Identify Sources of the Measured Concentrations

  • Investigated other sources of Emissions Inventory data (besides 1999 NEI with Chattanooga’s revisions)

    • 1999 TRI data

    • Georgia Title V permits for bordering counties

  • No significant findings of missing emission sources

  • Additional resource intensive field investigations, contact with State/Local governments, and/or contact of specific facilities with emission sources would be the next step

  • Additional CALPUFF modeling was conducted for Hamilton County sources using a refined meteorological grid

    • no significant differences from the results presented previously

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Additional Efforts to Identify Sources of the Measured Concentrations

  • Additional modeling done using EPA’s new AERMOD model for only the Hamilton County sources

    • results were different from the CALPUFF runs

    • in some cases, better agreement with monitor results, in some cases worse

    • overall, AERMOD results (like CALPUFF) under predicted the monitored values

  • Evaluation of 1999 NEI “non-point” and “on-road mobile” source emissions data

    • these were not included in our modeling because the NEI doesn’t provide specific locations, just totals for each county

  • Overall, emissions from non-point and on-road mobile sources were insignificant compared to major point sources

    • could contribute an unknown fraction to the monitored values, depending on the proximity of the sources to the monitors

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Modeling Conclusions Concentrations

  • Model to Monitor Comparison poor in many cases

    • mostly the monitored values were higher then modeled values

    • indicates that not all sources may have been identified or that the emission rates or source parameters may not be accurate

  • Local sources were found to be significant contributors to the model-predicted concentrations of chromium, manganese and nickel at the monitor locations, thus indicating that they are also likely contributors to the actual monitored concentrations.

  • In general, the large coal burning power plants located more than 50 kilometers from Chattanooga were not found to be significant contributors to the model-predicted concentrations at the monitor locations.

  • No large, local sources of arsenic emissions were found and the modeling did not show major contributions from the distant sources. Therefore, the primary sources of the elevated monitored levels of arsenic are unknown.

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Modeling Conclusions Concentrations

  • A detailed uncertainty analysis has not been conducted for this modeling study

  • As with any modeling study, there are many potential sources of uncertainty in the modeling

    • emissions inventory data

    • representativeness of the meteorological data

    • the model’s ability to appropriately represent the complex terrain in the Chattanooga area

    • appropriateness of the options selected when running the model

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CALPUFF Lessons Learned Concentrations

  • Takes a significant amount of time to learn how to run CALPUFF

  • Preparing the model inputs is resource intensive (especially CALMET met preprocessor)

  • MANY options are available for CALMET and CALPUFF Model Inputs – some require expertise of an experienced modeler

    • FAQ section of Earth Tech’s CALPUFF website is a helpful resource (

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CALPUFF Lessons Learned Concentrations

  • Didn’t have MM5 data for the time period of interest, so surface and upper-air data from multiple meteorological stations were used

    • Had to develop a program to convert the Integrated Surface Hourly surface data (ISHD) to a format CALMET could accept (CD-144 or SAMSON CD format)

    • Also filling data gaps in the FSL upper-air data was time consuming

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Conclusion Concentrations

  • Project was a good learning experience for me

  • I have much left to learn about using CALPUFF