1. Implications of AERMOD on a Chemical Plant William B. Jones Roger P. Brower Zephyr Environmental Corporation Columbia, Maryland Presented at 100 th Annual AWMA Conference and Exhibition Pittsburgh, PA June 26, 2007

2. Outline of Presentation Background on project Comparative Modeling –ISC3 –AERMOD Conclusions

3. Background on Project Chemical plant in southwestern Louisiana Several permitting efforts required modeling over the past few years (modeling done with ISC3) November 9, 2006: AERMOD replaced ISC3 as preferred dispersion model Chemical plant was curious as to what effect going from ISC3 to AERMOD would have

4. Three projects examined Vinyl Acetate –Modeling performed in 2005 –In support of Title V application for Plant’s polyethylene manufacturing complex Butadiene –Modeling performed in 2003 –In support of revised Title V application for Plant’s ethylene/styrene manufacturing complex PM10 –Modeling performed in 2003 –In support of “retroactive” PM10 NAAQS and PSD Increment modeling

5. Comparative Modeling Vinyl Acetate Original ISC3 modeling –Initially only Plant sources, then offsite sources –Flat terrain (no receptor elevations) –Meteorological data from 2004 (Lake Charles surface and upper air) AERMOD modeling –Plant sources only –Flat terrain (no receptor elevations) –Meteorological data from 2004 (Lake Charles surface and upper air) processed using AERMET Bowen Ratio, Albedo, and Surface Roughness Lengths assumed constant for entire area

6. LDEQ Default Meteorological Values Taken from “Developing State-Wide Modeling Guidance for the Use of AERMOD, A Workgroup’s Experience” (Presented at 2005 Louisiana AWMA Fall Conference)

7. Comparative Modeling Vinyl Acetate: ISC3 Results Source Highest predicted 8-hr concentration (ug/m3) 203202.63 BDRYER2148.28 BDRYER336.93 BEXTRDR36.50 BPELLET822.22

8. Comparative Modeling Vinyl Acetate: AERMOD Results Source Highest predicted 8-hr concentration (ug/m3) 203350.53 BDRYER2113.48 BDRYER389.01 BPELLET332.40 BPELLET431.90

9. Comparative Modeling Vinyl Acetate: Q-Q Plot, AERMOD and ISC3

10. Comparative Modeling Vinyl Acetate Observations Highest contributing source is same with ISC3 and AERMOD Highest source-specific impacts for each model roughly the same AERMOD consistently over predicts relative to ISC3 (for highest 8-hr concentrations)

11. Comparative Modeling Butadiene Original ISC3 modeling –Initially only Plant sources, then offsite sources –Flat terrain (no receptor elevations) –Meteorological data from 2000 (Lake Charles surface and upper air) AERMOD modeling –Plant sources only –Flat terrain (no receptor elevations) –Meteorological data from 2000 (Lake Charles surface and upper air) processed using AERMET Bowen Ratio, Albedo, and Surface Roughness Lengths assumed constant for entire area

12. Comparative Modeling Butadiene: ISC3 Results Source Highest predicted annual concentration (ug/m3) 1296_D10.15047 WPT35_980.12538 12_96C0.10160 WPT34_960.09661 1296_D20.09648

13. Comparative Modeling Butadiene: AERMOD Results Source Highest predicted annual concentration (ug/m3) 5_89A_S11.20429 5_89A_S20.39604 WPT34_960.37479 5_89A_W10.28529 5_89A_S30.25612

14. Comparative Modeling Butadiene: Q-Q Plot, AERMOD and ISC3

15. Comparative Modeling Butadiene Observations Major contributing sources in ISC3 are not consistent with those in AERMOD Highest source-specific impacts for AERMOD are higher (roughly an order of magnitude) than ISC3 AERMOD consistently over predicts relative to ISC3 (for highest annual concentrations)

16. Comparative Modeling PM10 Original ISC3 modeling –Initially only Plant sources, then offsite sources –24-hr and Annual NAAQS and PSD Increment –Flat terrain (no receptor elevations) –Meteorological data from 1996-2000 (Lake Charles surface and upper air) AERMOD modeling –Plant and offsite sources –24-hr NAAQS only –Flat terrain (no receptor elevations) –Meteorological data from 1996-2000 (Lake Charles surface and upper air) processed using AERMET Bowen Ratio, Albedo, and Surface Roughness Lengths assumed constant for entire area

17. Comparative Modeling PM10: ISC3 Results (1996) Source Highest second-high predicted 24-hr concentration (ug/m3) LC_COAL44.01368 9_8920.45634 FIRE_6519.61712 CIT13_1818.37893 8_8916.53271

18. Comparative Modeling PM10: AERMOD Results (1996) Source Highest second-high predicted 24-hr concentration (ug/m3) LC_COAL72.12283 FIRE_6530.69010 STY20_9023.74922 8_8919.89097 9_8918.35552

19. Comparative Modeling PM10: Q-Q Plot, AERMOD and ISC3 (1996)

20. Comparative Modeling PM10 Observations Major contributing sources in ISC3 are consistent with those in AERMOD –The two Plant sources in the Top 5 for ISC3 and AERMOD only had increases in their predicted 24-hr concentrations of 20% and 12% going from ISC3 to AERMOD (larger increases from offsite sources) Highest source-specific impacts for AERMOD are higher than ISC3 AERMOD and ISC3 are consistent in lower concentrations (AERMOD sometimes slightly lower), but at higher concentrations AERMOD over predicts relative to ISC3 (for highest second-high concentrations)

21. ConclusionsConclusions Examined vinyl acetate, butadiene, and PM10 modeling AERMOD nearly always predicted higher concentrations than ISC3 –For some lower PM10 concentrations AERMOD slightly under predicted relative to ISC3 Plant should exercise caution in future permitting efforts that involve updated previous dispersion modeling analyses

22. Contact Information Zephyr Environmental Corporation 10420 Little Patuxent Parkway, Suite 320 Columbia, Maryland 21044 Bill Jones 410-312-7910; bjones@zephyrenv.com visit us at www.ZephyrEnv.com and www.HazMatAcademy.com